EEVblog #525 - Bank Note Acceptor Teardown

[EEVblog]

What's inside an old style bank note/bill accptor/validator for vending machines and the like?
How does it detect genuine notes from dodgy ones?
Datasheets:
http://www.silonex.com/datasheets/specs/images/pdf/102136.pdf
http://pdf.datasheetcatalog.com/datasheets/134/157244_DS.pdf
http://www.ti.com/lit/gpn/tlv5629
http://www.mouser.com/ds/2/328/top242-250-9213.pdf
http://www.latticesemi.com/~/media/Documents/DataSheets/ispMACH4ADataSheetvL.ashx?document_id=1344
http://www.freescale.com/files/microcontrollers/doc/data_sheet/MC68HC11F1.pdf
http://pdf.datasheetcatalog.com/datasheet/AdvancedMicroDevices/mXwuvz.pdf

[c4757p]

Hmm... I wonder why it won't accept the bill. They're grumpy sometimes with crusty old money, but there's no trick to it...

...never mind...

[sync]

I guess it must be enabled from the vending machine controller. When the machine is not working the acceptor should not accept notes.

[mikeselectricstuff]

Centre sensor more likely to be shorter wavelength due to larger PD. May be looking for fluorescence on some of the inks. You should fire the LEDs up to see what colour(s) are visible.

As regards the poor mains  segregation - well it is only 110V, not like it's real mains  or anything...
 

[c4757p]

From Dave in the YT comments:

I got a $1 coin in the? US one time (from a machine?), and tried to spend it, I got the WTF face.

If you really want to get the WTF face, try spending a $2 bill... Fifty cent coins are good too. At least the $1 coins were pushed somewhat recently

[orion242]

Another great video.

That's a newer $5 bill that was introduced in ~06.

I second a followup video to power it up and figure out what spots in the bill they are looking at and with what wave lengths they are using.  Maybe dump the rom and poke at the firmware.

[gsstyle]

Oh, My i haven't though about a 2 dollar bill in a long time , have collected some .. and i think i gave them to my mom .. so i wouldn't spend them , but were talking mid 90's

[EEVblog]

Hmm... I wonder why it won't accept the bill. They're grumpy sometimes with crusty old money, but there's no trick to it...

Could be the firmware (becaue the note is 2006 I'm told), but could also just need a good clean.

[EEVblog]

If you really want to get the WTF face, try spending a $2 bill... Fifty cent coins are good too. At least the $1 coins were pushed somewhat recently

I've got a $200 Australian coin, try spending that!

[gxti]

Clearly, safety isolation was not required for this application. The layout is still baffling, though.

[NickS]

Hmm to beat this could you use some clear plastic (overhead projector) and just print a pattern in black to reproduce the signal that the reader is expecting?
Bonus points if you dump the ROM and use it to create the patterned image.

Sure it would only work on a single type of machine, but if it is common enough and you can get the plastic cheap enough it could be a fun exercise - pity about the illegal bit.

[DavidDLC]

No offense Dave, but can you clean your throat before you make a video ?

On the lates videos is kind of annoying that hoarseness on your voice, it almost stop me to go all the way to the end of the video.

David.

[EEVblog]

No offense Dave, but can you clean your throat before you make a video ?

The video is 40 minutes long, with over an hour of recorded material, recorded over several hours with 60 or so clips. I can't just "clear my throat before I make the video".
I do clear my throat if I hear it's getting a bit rough. Sometimes I stop the camera and do that and will reshoot that bit. But I'm not actively listening for that stuff while shooting. it's like trying to detect if you are speaking too loud, or too fast, or have repeated something, or have said something wrong. It's very difficult, you simply don't notice your own voice and what it's doing.
My voice sucks in so many way, and occasional hoarseness is simply part of that I'm afraid, it will happen.
I also generally cannot go back and re-shoot segments if I detect my voice is bit rough at the video editing stage.
So sorry, I do my best, but you get what you get.

[David_AVD]

Coin and not acceptors usually have an enable line from the host machine.  This is so they don't accept money before the machine is ready or if it's "out of stock".  That can be another reason for them not accepting the cash.

EDIT: Didn't see the reply from "sync" about the enable line.   

[ampdoctor]

I guess it must be enabled from the vending machine controller. When the machine is not working the acceptor should not accept notes.

That's exactly what's going on.  this makes sure your money doesn't get swallowed up by a machine that's empty or malfunctioning in some way or another. Otherwise these things are dead reliable electrically.  Their biggest issues as dave noted is that the mechanicals and optics get absolutely filthy. After you push maybe a thousand bills through it you need to just open the thing up clean off the feed belts and sensors and you're "money"

as an aside, these things aren't really about detecting counterfeits, there's really very little of that going on, but rather to make sure the bill is the right denomination.

[DavidDLC]

No offense Dave, but can you clean your throat before you make a video ?

The video is 40 minutes long, with over an hour of recorded material, recorded over several hours with 60 or so clips. I can't just "clear my throat before I make the video".
I do clear my throat if I hear it's getting a bit rough. Sometimes I stop the camera and do that and will reshoot that bit. But I'm not actively listening for that stuff while shooting. it's like trying to detect if you are speaking too loud, or too fast, or have repeated something, or have said something wrong. It's very difficult, you simply don't notice your own voice and what it's doing.
My voice sucks in so many way, and occasional hoarseness is simply part of that I'm afraid, it will happen.
I also generally cannot go back and re-shoot segments if I detect my voice is bit rough at the video editing stage.
So sorry, I do my best, but you get what you get.

Ok I really appreciate your answer. No problem at all.

[Orpheus]

Not having the bill chamber in place may affect it as well

[David_AVD]

Not having the bill chamber in place may affect it as well

Good point.  Otherwise the money would spill into the machine.

[lilshawn]

those milky white LED's are actually BI color LED's...I can see the 3 leads through the side.

I work as a service tech for arcade and vending machines. we don't use coin controls model of bill acceptor, but we do use their coin acceptors though. Money Controls is a popular company in North America, as is ICT (International Currency Technologies - the brand of bill acceptor we use has a far superior sensor system). Money controls has the better coin acceptor and ICT has a better note acceptor. I'm not real fond of Money Controls, and I'll tell you why...

Money Controls is a real bugger about their firmware. They make you buy a ridiculously expensive TTL to RS232 converter box (that retails for about $1500US) that you must use to update the firmware through the diagnostic port.

Then, to obtain the firmware, you must use their program to download the firmware data as a .zip file (not a big deal) but then they lock the zip files with a password that you have to know it in order to unzip it to obtain the raw BIN file.

then... (yeah, then) they make it so you have to pay a yearly subscription licence to run the program that updates firmware. A different program is used for each model of acceptor and you must buy a licence for each program. (IE if you have 4 different type of acceptors you need 4 different programs and 4 different licences)

ICT does not make you pay for updates. you buy a handheld programming device and then have ICT send you the firmware and you download it to the device and use the handheld device to dump the firmware to the acceptor. a much friendlier experience overall.

[EEVblog]

those milky white LED's are actually BI color LED's...I can see the 3 leads through the side.

Doh, yes, you are right, I should have looked at the pins on the bottom.

[Razor512]

The $1 bills have almost no security at all, though it is not likely that someone will make a fake $1 since they are likely to be more expensive to counterfeit.

The bill with the most security is the $20 bill as it is the most common one to be faked. (most businesses will not accept $100 bills)

The security on a $1 bill is just the paper used (reacts with those money testing pins)

then the images on the  money are printed with a special patter that identifies the money type to the machine (it is also why some scanners will detect if you are trying to scan in money. (even if it is just a partial scan.

(the security on the US paper money are similar to the digimarc watermarking method where it creates an extremely subtle grain pattern over the entire image (for a photo taken pretty much all cameras will have more noise native to the image than the digimarc so it is invisible in most cases.

(not sure how  good the security on a $100 bill  is, but for the $20 bill, it has the largest number of indicators that are easily visible since for most stores, ti is the most common bill used and workers need to be able to verify them quickly.

PS the bills above $1 also insert fibers  (though they are randomized) that react to UV light. due to the way they are placed, they must be added to the paper in the earliest stages when the paper it's self is being made.

I will try to take some pics of the security used on some different bills

[c4757p]

The security on a $1 bill is just the paper used (reacts with those money testing pins)

IIRC the Treasury has itself stated that these pens are unreliable.

My idea of $1 bill security is "it's real if it doesn't say 'Monopoly'", since as you said, nobody would be able to economically counterfeit them.

[EEVblog]

those milky white LED's are actually BI color LED's...I can see the 3 leads through the side.

Doh, yes, you are right, I should have looked at the pins on the bottom.

I can confirm the 4 LED's in the middle of the note are dual colour red and IR. Two outside ones are UV.

[EEVblog]

The bill with the most security is the $20 bill as it is the most common one to be faked. (most businesses will not accept $100 bills)

I remember getting many strange looks of suspicion when using $50 notes in the US, and a couple of refusals. And when questioned it wasn't because of a lack of change available. I've had tellers even check my $20 notes too.
That never happens here (unless they don't have the change). $50 notes are common as mud, and no one bats an eyelid at accepting a $100 note. Although ATM's don't give out $100 notes, so they aren't nearly as common.

[Alexei.Polkhanov]

I just realized that I have not used cash money at all for several months, not even once.
Month ago first time I got to the electronics supply store store and there was a sign "No cash please. Thank you for understanding". I guess they don't want to go to bank after hours 

[99tito99]

I read an interesting essay (wow about 25 years ago) about the extent of US currency forgery and how the US Treasury came up with a plan.  Unfortunately, because there were so many forged US dollars in the World that their plan collapsed the World economy.  The “Plan” was that the US Treasury secretively printed every paper denomination using red ink and distributed the notes to the banks. Then one Monday morning they announced that by Friday all green US notes had to be exchanged with red ones. Needless to say all the drug, underworld, offshore, counterfeit and other funny-money become worthless, and the World economy collapsed.

But, how remote is the possibility that the US government could do this in secrecy and that the “Big-Wheels” wouldn’t figure out a way to get red money to the drug, underworld, offshore, counterfeit and other funny-money guys before that Monday. . .

Cheers, Mark * * *

[David_AVD]

...Although ATM's don't give out $100 notes, so they aren't nearly as common.

I'm 99% sure I've gotten $100 notes from an ATM, so it must vary by bank.

[EEVblog]

I'm 99% sure I've gotten $100 notes from an ATM, so it must vary by bank.

Yeah, likely.
I use Commbank.

[nkinnan]

Dave, your video indicates you think this uses the edge detection to wait for a specific position on the bill and then record a "snapshot" of the detector values.  It may not be so simple. 

I'd guess that with the two edge detectors (and assuming a constant feed rate) they start reading out data at reasonably high speed (a few KHz perhaps?) then stop at the second edge and compare the waveform from each detector to a standard.  Particularly with the "through the paper" readouts, this could identify watermarks by their "waveform" as they pass by (higher brightness when looking through a watermark as your "pen light behind the bill" showed) among other things (detecting the interrupt from the security strip?)

This would be a much more robust way of identifying bill denomination and authenticity than taking a "snapshot" from the 6 points at an instant in time.  In fact I doubt the "snapshot" method you guessed would be able to disambiguate different denominations.

Great tear-down and a very interesting piece of equipment regardless.  If you do a follow-up (I vote for one) this may be an avenue of investigation depending on how "deep" you want to go.  As a resident of the US, I would also be happy to send you some older bills (pre-2006) for testing though I suspect other commenters are correct that it will reject any bill without an "enable" input from the parent machine on one of those connector pins so the newness of the bill may not be the problem.

[EEVblog]

Yes, it's quite likely it does some form of entire bill capture and then comparison with an existing scanned template.
Not sure at what points it would switch the red and IR leds though?

[adythewolf]

A little while back, I've repaired a rather obscure device, used to fool slot machines into thinking they received the money. (low on money, the payment was good... I'm ashamed of myself).
Well, this device ran on several 9V batteries and used a strange anthenna.
Needless to say, it worked on slot machines, I'm not sure how it would behave on something like this and I'm not keen on testing it.

[nkinnan]

Yes, it's quite likely it does some form of entire bill capture and then comparison with an existing scanned template.
Not sure at what points it would switch the red and IR leds though?

If you mean WRT the dual-emission (three pin) LEDs, then switching between the two wavelengths in sync with the ADC clock, they could capture "two waveforms in one" at half the sampling rate.  They could turn the 6 detector channels into 8 with 4 of them at half-resolution in the time domain.  Just a guess. 

[G7PSK]

I dont know when the first bank note detectors were introduced, but in the early 1970's a garage at Stretham near Cambridge introduced an all night pump that dispensed 2 gallons of petrol when a ten shilling note was inserted. It was taken out of service within a few weeks when people started to use a photocopy of notes in the machine, you did not even need to copy both sides or in colour to fool the machine so it must have been very simple indeed.

[David_AVD]

I'm guessing the people that designed that acceptor got hauled over the coals.   

[mikeselectricstuff]

Yes, it's quite likely it does some form of entire bill capture and then comparison with an existing scanned template.
Not sure at what points it would switch the red and IR leds though?

My guess would be they continuously alternate it and measure the difference, to measure the inks' relative spectral characteristics.

[G7PSK]

I'm guessing the people that designed that acceptor got hauled over the coals.   

Don't know about that, but when it was installed there was half a page in the local newspaper with a picture of the garage owner (a Mr. Pinion) I never got to use the machine as it was only operational at night but I saw it for many years,it was as big as a large petrol pump and stood on its own island on the forecourt, you had to walk over to it put your money or photocopy in then select the pump and grade you wanted. I know that it cost a lot of money forget how much though and was one if not the first in the country.

[komet]

It looks like you might be able to put a bill in with double-sided sticky tape on it and a pullback strip, and could steal money out of the storage box with it.

[David_AVD]

It looks like you might be able to put a bill in with double-sided sticky tape on it and a pullback strip, and could steal money out of the storage box with it.

I'm not sure it would be as easy as that sounds.  I'm guessing some note acceptors have an alarm output that activates when it notices the note going the wrong way, etc.

[Stonent]

The yellow ink number pattern is partially to prevent photocopying of the money.

http://en.wikipedia.org/wiki/EURion_constellation



They say the #1 feature of US money in fighting counterfeiting is just the feel. In your hand, nothing else feels like it.

[Stonent]

It looks like you might be able to put a bill in with double-sided sticky tape on it and a pullback strip, and could steal money out of the storage box with it.

I'm not sure it would be as easy as that sounds.  I'm guessing some note acceptors have an alarm output that activates when it notices the note going the wrong way, etc.

In school I remember seeing a student with a 1$ bill with a long strip of clear tape attached to both sides. He'd feed the money in, purchase the drink and pull it back out.

[adh]

As regards the poor mains  segregation - well it is only 110V, not like it's real mains  or anything...

A while ago I've seen insides of 230V/50Hz coke machine and there was quite beefy 230V->110V transformer (probably even isolated) and everything ran off it's output (except fluorescent lights on the front), service manual for said machine looked like that transformer is there even for 110V variant (it was labeled "Power conditioning" or something like that on block diagram). It seems to me that lot's of vending machine related hardware just runs off 110V AC because these machines tend to have internal 110V AC protected (and maybe isolated) power bus regardless of what mains voltage they are for. Another thing of note was that the control circuitry for the actual can dispensing mechanism was essentially a bunch of 110V switches and relays.

[Winston]

I don't understand the complaint about AC power input ground plane clearance.  It seems to more than comply with this:

http://www.smps.us/pcbtracespacing.html

Spikes should be limited to the clamping voltage of the MOVs.

[ExoUY]

Hi guys, Dave.
First of all, sorry for my English!
I'm Alvaro from Uruguay, I always follow your videos but never posted on the forums.
This time I think I can add some info as I work as a Casino technician
If you guys don't mind my bad English I would like to record a video response showing a newer BVal and the general working later today (I have to wait for my boss to leave).
But in general you are right about the way the BVal works

[ExoUY]

A little while back, I've repaired a rather obscure device, used to fool slot machines into thinking they received the money. (low on money, the payment was good... I'm ashamed of myself).
Well, this device ran on several 9V batteries and used a strange anthenna.
Needless to say, it worked on slot machines, I'm not sure how it would behave on something like this and I'm not keen on testing it.

Ahhh that device...
What it does is generate a magnetic pulse that would confuse mainly the coin acceptor on the machines (sometimes the bill validator too).
It's true, that used to work, nowadays is harder, and if you get caught using it you end up in hail (at least here).

[Winston]

I don't know what the dollar bill situation is in Australia.  Perhaps someone can send you a pre-2002 dollar bill that's still in good shape so you can see if this unit will actually accept it.

[JackOfVA]

I looked at a US$ 5 and US$ 20 bill under UV light - images attached.

The $5 has no ID strip, but I did see a quasi-random UV image centered on Lincoln's image.  Not sure if this is real or something that has transferred to the bill.

The $20 has the embedded security strip which glows green. However, three of the four corners also fluoresced - but the uneven pattern looks unintentional.

 

[Razor512]

@JackOfVA which model of dollars were you using, the ones I tested were from 2009, they tend to move the security strips and mix and match different patterns and UV reactive elements with each model


===-=-=--==--==-=-=--=

Here are some images of how the dollars look under UV light.

My camera does not capture it very well, eg it does not capture some of the variations in the fibers and how they react to the UV light

but each value reacts differently to the light

Here are some examples:

$5   

$20

($20 has the security strip in a different location, and makes use of a few different fiber types which all react differently to the UV light, causing a a few different subtly different shades of of the color of the bill to appear. (couldn't get the camera to capture them) (the $20 also uses reflective ink with some glitter in parts of the image, but under UV light, they are completely non reactive and lose their glitter effect)

$1   

The $1 has a very uniform response to the UV light (they most likely use cheaper paper and ink)

For the bills where verifying the authenticity is important, they use many different fibers and inks which react to different forms of light in specific ways. the formulas are also likely kept secret, thus making it pretty much impossible for someone to make a fake one and have it pass every test.

The down side is that it is also easy to fail the test when it comes to machines. Due to the paper and ink used, they are not the most resilient and thus after a while, they will become  useless in higher end machines, for example a dollar that is beginning to fade may not pass the test that the ATM machines that accept cash deposits may do, but will work just fine in a vending machine.


=-=-=-=-=-=-=-=-

A side note, never buy anything from a vending machine. I don't understand why someone will willingly pay 3-5 times the retail price for a snack or some soda.

 A large case of soda quantities over 100, generally comes out to around 13-14 cents a bottle (16oz or around 473ml) if you get them wholesale, most stores will then charge $1 per 16oz bottle which is already an insane price especially since a 2 liter (2000ml) bottle is also $1. Then you will have vending machines that will charge in many cases, as much as $2.50 for the soda, and you still see people buying stuff from them.

The vending machines at the college I go to, generally have a long line at the vending machines. (I thought you had to have an IQ above 5 to get into college, but apparently they now allow people to push the limits of negative numbers in terms of IQ )

[synapsis]

I looked at a US$ 5 and US$ 20 bill under UV light - images attached.

The $5 has no ID strip, but I did see a quasi-random UV image centered on Lincoln's image.  Not sure if this is real or something that has transferred to the bill.

The $20 has the embedded security strip which glows green. However, three of the four corners also fluoresced - but the uneven pattern looks unintentional.

I wonder if the UV on the edges of the $20 is from a dye pack that banks use to identify stolen notes. Maybe one leaked onto the edges of the notes. 

Lately I've started to notice the local gas stations around here are checking $5 notes for forgeries. I asked the cashier and she said they get a fake $5 note at least twice a month!

I've seen a few documentaries on the production of US money, and they're very interesting. The cotton paper is made at one company in Pennsylvania or Connecticut or something, and it has always been that one company. I'd be really interested to see a docu on more modern notes like every country except the US uses. We've been using "greenbacks" for 100 years or more.

[JackOfVA]

The $5 bill is series 2006. The $20 is series 2004A.  Didn't have a $1 on hand to try.

[ExoUY]

Ok, still waiting for the boss to leave so I'll write a little about this devices.
This type of validators are kinda old (later when I record the video I'll show the newer ones ), they work by comparing known characteristics of bills against the on board "bill table" (thats what's inside the flash prom), I guess that in this old model that's together with the firmware, in modern ones you can choose to update the bill table, the firmware or both.
To build these bill tables manufacturers takes lots of samples of bills and make an average reading of the sensors, thats stored in one slot of the table (let's say the slot for the $5 bill).
When you want to buy something and insert the bill, the validator compares the readings of the sensors and if they are in a certain threshold compared to a value of the table they recognize the value and authenticity of the bill, stack it and send the ACK data or pulses to the machine. 

As of why the colors of the LED's, the wavelength, etc, each manufacturer have they own scheme of sensors, light, etc that they trust and advertise as a better way of detecting.

Money controls (nowadays Crane Payment Solutions) makes good validators, I would place it #2 on my top 3 of Bvals for Casinos.

Ah, a little story about the building of bill tables.
Some time ago my country put on the streets a re print of a common bill, but they quietly changed the printing company. I started to get complains from casino operators about the rejection rate of bills increasing, so we discovered the re print, it was quite easy as the bills have a micro logo of the press that makes them and it was a different one
We talked to one of the manufacturers of Bvals and they sent me a software and firmware that would read and dump the sensors readings (sadly it was all encrypted). After sending them this files (one for each of the 4 "sides" of the bill) they told us that we were right and that some characteristics of the paper were different, so they needed to issue a new bill table. The funny part; they asked us if we could send them 200 bills of this type, so we sent a guy to the bank, where he was kept on hold while he was asked questions about why he needed this bills, and they called the central bank of our country, the police and us! It was quite a mess!

Ok that was long! If you made it this far, sorry for my bad english! And please ask away!

[Stonent]

I looked at a US$ 5 and US$ 20 bill under UV light - images attached.

The $5 has no ID strip, but I did see a quasi-random UV image centered on Lincoln's image.  Not sure if this is real or something that has transferred to the bill.

The $20 has the embedded security strip which glows green. However, three of the four corners also fluoresced - but the uneven pattern looks unintentional.

I suspect the glowing corners of the money are glowing for the same reason a crime scene glows. 

[Stonent]

Here are the last 3 $5 bills



So the one that Dave had was the last one from 2006. If the firmware was 2002 it would be looking for the one in them middle that came out around 1996 or so. The one on top is of the same redesign period that the current $1 bill is.

The $1 bill has not really been changed since the 50s or 60s if I recall correctly. Last I heard, it was just not economically feasible to redesign it. When they did the major bill redesign in the late 90s they added color shifting ink. On some bills there was a logo and on some it was the treasury seal.  If tilted it alternates between green, gold and black.

A number of years ago I did see a counterfeit bill that would pass the pen test. Because the person appeared to have printed the the bill on some sort of waxed paper.  Since waxed paper won't absorb the ink, it doesn't turn colors.

The bill failed the feel test pretty badly. Surprisingly this bill came as change to one of my dad's ex girlfriends.  She decided to keep the fake $1 bill as a novelty piece.

The last documentary I saw on how money was made showed they purchased the scraps and trimmings from a blue jeans factory as part of the base of the bill.

[JackOfVA]

I looked at a US$ 5 and US$ 20 bill under UV light - images attached.

The $5 has no ID strip, but I did see a quasi-random UV image centered on Lincoln's image.  Not sure if this is real or something that has transferred to the bill.

The $20 has the embedded security strip which glows green. However, three of the four corners also fluoresced - but the uneven pattern looks unintentional.

I suspect the glowing corners of the money are glowing for the same reason a crime scene glows. 

It seems that cocaine fluoresces green under UV light.  This might imply that this bill has drug residue.  I had 3 $20's in my wallet and only one had the corner fluorescence.

[Stonent]

I looked at a US$ 5 and US$ 20 bill under UV light - images attached.

The $5 has no ID strip, but I did see a quasi-random UV image centered on Lincoln's image.  Not sure if this is real or something that has transferred to the bill.

The $20 has the embedded security strip which glows green. However, three of the four corners also fluoresced - but the uneven pattern looks unintentional.

I suspect the glowing corners of the money are glowing for the same reason a crime scene glows. 

It seems that cocaine fluoresces green under UV light.  This might imply that this bill has drug residue.  I had 3 $20's in my wallet and only one had the corner fluorescence.

I guess only one had been inserted into a dancer's bill validator? 

[ExoUY]

well, that was horrible! But anyways I will post the video, again, sorry for my bad English also I get nervous and start repeating the same words :$
http://youtu.be/rqMqUsUidAk
(it will take a couple of hours to upload.
But to repair the shame of such a bad video, here's a goody I remembered I had on the wall of my lab:


Uploaded with ImageShack.us

It's for a Bvall that uses the same tech as the one Dave disassembled
Hope someone finds it interesting .

[grumpydoc]

I don't understand why someone will willingly pay 3-5 times the retail price for a snack or some soda.

Usually because the vending machine is placed somewhere that your options are limited, ideally where you're more likely to want a drink or snack.

e.g in the gym foyer - you're hot, thirsty and possibly a little hungry after your work-out and the nearest shop is a mile away - what do you do? Walk to the shop or just stump up the inflated price for something from the machine?

[David_AVD]

I don't understand why someone will willingly pay 3-5 times the retail price for a snack or some soda.

Usually because the vending machine is placed somewhere that your options are limited, ideally where you're more likely to want a drink or snack.

e.g in the gym foyer - you're hot, thirsty and possibly a little hungry after your work-out and the nearest shop is a mile away - what do you do? Walk to the shop or just stump up the inflated price for something from the machine?

I saw an online trade article where one of the drink manufacturers (Pepsi or Coke) were going to trial a vending machine that varied the price according to the local conditions.  eg, It discounted the sell price when the weather was bleak and sales were low.

[nitro2k01]

What's the talk about the flash chip needing to be connected to the CPLD to program it? You can program it using 5V only, and commands that can be issued as writes from the CPU. I even think the AM29Fxxx series will let you read the rest of the array while one sector is being erased or programmed, but even if that were not the case, you could easily copy a small programming routine to RAM and run it from there. You can also lock individual sectors through hardware, which then requires 12V programming in order to unlock, so you don't have to worry about locking yourself out in case of a bad in-circuit programming. The IS61C256 is a 32 kB SRAM chip, for what it's worth.

The difference in the sensors on the sides, vs the big one is obviously that ones on the sides are detecting light through the bill whereas the big one is detecting reflected light (thus the white blocking panel.) If you want to determine for certain whether an LED is IR or UV, hold an object (like maybe a bill ) and see if it fluoresces.

When I ripped the IR pass filter out of my camera, I took an IR LED and took some pictures of Swedish bank notes:

20 kr:

Swedish 20 kr note in IR light by nitro2k01 (Gameboy Genius), on Flickr


Swedish 20 kr note in IR light by nitro2k01 (Gameboy Genius), on Flickr


Swedish 20 kr note in IR light by nitro2k01 (Gameboy Genius), on Flickr

In visible light:


100 kr:

Swedish 100 kr note in IR light by nitro2k01 (Gameboy Genius), on Flickr


Swedish 100 kr note in IR light by nitro2k01 (Gameboy Genius), on Flickr
(This is the reflective strip.)

In visible light:


Those are the kinds of tricks you'd be looking at on just about all notes, probably. Something like half of the note is completely white in IR light, so you'd probably need a very specific kind of ink that completely reflects IR while it absorbs red light well.

[Stonent]

Winston Churchill is watching you spend.

(Ok well it looks like him anyway)

[firehopper]

actually, from what I remember.. all US bills use the same paper.. Thats likely to never change.. its a form of rag paper..

@JackOfVA which model of dollars were you using, the ones I tested were from 2009, they tend to move the security strips and mix and match different patterns and UV reactive elements with each model


===-=-=--==--==-=-=--=

Here are some images of how the dollars look under UV light.

My camera does not capture it very well, eg it does not capture some of the variations in the fibers and how they react to the UV light

but each value reacts differently to the light

Here are some examples:

$5   

$20

($20 has the security strip in a different location, and makes use of a few different fiber types which all react differently to the UV light, causing a a few different subtly different shades of of the color of the bill to appear. (couldn't get the camera to capture them) (the $20 also uses reflective ink with some glitter in parts of the image, but under UV light, they are completely non reactive and lose their glitter effect)

$1   

The $1 has a very uniform response to the UV light (they most likely use cheaper paper and ink)

For the bills where verifying the authenticity is important, they use many different fibers and inks which react to different forms of light in specific ways. the formulas are also likely kept secret, thus making it pretty much impossible for someone to make a fake one and have it pass every test.

The down side is that it is also easy to fail the test when it comes to machines. Due to the paper and ink used, they are not the most resilient and thus after a while, they will become  useless in higher end machines, for example a dollar that is beginning to fade may not pass the test that the ATM machines that accept cash deposits may do, but will work just fine in a vending machine.


=-=-=-=-=-=-=-=-

A side note, never buy anything from a vending machine. I don't understand why someone will willingly pay 3-5 times the retail price for a snack or some soda.

 A large case of soda quantities over 100, generally comes out to around 13-14 cents a bottle (16oz or around 473ml) if you get them wholesale, most stores will then charge $1 per 16oz bottle which is already an insane price especially since a 2 liter (2000ml) bottle is also $1. Then you will have vending machines that will charge in many cases, as much as $2.50 for the soda, and you still see people buying stuff from them.

The vending machines at the college I go to, generally have a long line at the vending machines. (I thought you had to have an IQ above 5 to get into college, but apparently they now allow people to push the limits of negative numbers in terms of IQ )

[philpem]

It seems unlikely to me that the note acceptor is using UV. Those photodiodes aren't going to detect UV at all -- the glass lenses will block it quite effectively. Also most UV LEDs I've seen are clear; the smoked plastic is generally reserved for infrared LEDs.

I've had a dig around (Google search: banknote acceptor infrared) and found some interesting stuff:

A patent on an infrared banknote acceptor - http://www.google.co.uk/patents/US6903342  (actually an IR camera, LCD display and IR illuminator intended to help cashiers spot forged banknotes). Interesting because the patent includes an image of a US $100 bill... complete with the IR pattern

A few more images of US and Canadian banknotes under IR illumination: http://www.fraudfighter.com/counterfeit-detection-id-verification/bid/54918/Counterfeit-Detection-Infrared-Scanners-UV-Lights-Multi-Testers

And some information on the Bank of England's testing procedure for "banknote handling machines" -- http://www.bankofengland.co.uk/banknotes/Documents/retailers/framework.pdf
(TL/DR: bill acceptor manufacturers can ask the Bank of England for access to a selection of English banknotes for testing purposes)


I suspect the acceptor Dave has is alternating between red and IR very quickly during the scan and saving both data points for each position. I suspect this is to stop some cheeky so-and-so from making a forged note using red and black ink -- red for the "IR bands" and black for everything else. The real banknote ink probably passes IR but blocks red (and the rest of the visual spectrum). That probably means you have four possibilities:

Reflects red, reflects IR -- "unprinted"
Reflects red, blocks IR -- IR blocking ink (possibly not used)
Blocks red, reflects IR -- IR-transparent black (as seen on US banknotes)
Blocks red, blocks IR -- "black"

Interesting technology.


It looks like this is Money Controls' latest attempt -- http://www.google.co.uk/patents/US8232867 . Perhaps one of their other patents covers Dave's acceptor?


--- EDIT 20130926 0053BST -- It looks like Coinco have taken over the Money Controls MC2600 series -- here's the manual: http://www.coinco.com/index.php/support/downloads/category/14-bill-acceptors?download=48:mc-series-operations-and-service-manual

--- EDIT 0104BST -- Some information on the "Vend Serial" (MDB) protocol -- http://vending.org/images/pdfs/technology/mdb_version_4-2.pdf

--- EDIT 0108BST -- And someone's hooked one up to an Arduino... http://secrettweakerpad.blogspot.co.uk/2012/03/controlling-vending-machine-bill.html

[eliocor]

Dave, are you sure some of the LEDs are UV?
If they were made several years ago, in general their cases were TO18 with glass window and not plastic.
Also transparent plastic like those in the reader is in general opaque to UV light.

The best way to check the wavelenght of your LED is to use your multimeter in the "check diode" position and to measure the forward voltage drop. It should be about:
Wavelenght (nm) / color / Vf

940

Infrared

1.5

880

Infrared

1.7

635

High Eff. Red

2.0

605

Orange

2.2

585

Yellow

2.4

555

Green

2.6

450

Blue

3.0/3.5

360-405

Ultraviolet

3.5

[orion242]

I looked at a US$ 5 and US$ 20 bill under UV light - images attached.

The $5 has no ID strip, but I did see a quasi-random UV image centered on Lincoln's image.  Not sure if this is real or something that has transferred to the bill.

The $20 has the embedded security strip which glows green. However, three of the four corners also fluoresced - but the uneven pattern looks unintentional.

I suspect the glowing corners of the money are glowing for the same reason a crime scene glows. 

It seems that cocaine fluoresces green under UV light.  This might imply that this bill has drug residue.  I had 3 $20's in my wallet and only one had the corner fluorescence.

I guess only one had been inserted into a dancer's bill validator? 

LOL!!!  Dirty money, dirty, dirty money....

[Alexei.Polkhanov]

The best way to check the wavelenght of your LED is to use your multimeter in the "check diode" position and to measure the forward voltage drop. It should be about:
Wavelenght (nm) / color / Vf

940

Infrared

1.5

880

Infrared

1.7

635

High Eff. Red

2.0

605

Orange

2.2

585

Yellow

2.4

555

Green

2.6

450

Blue

3.0/3.5

360-405

Ultraviolet

3.5

Where does this come from? Does not match my experimental data - see images below.

Wikipedia sort of agree with this table. I wonder if I am measuring it right.

[loveman]

If you really want to get the WTF face, try spending a $2 bill... Fifty cent coins are good too. At least the $1 coins were pushed somewhat recently

I've got a $200 Australian coin, try spending that!

Obama thought about minting a trillion dollar coin to bypass debt limit.

[loveman]

The security features on modern bills are mostly aimed at allowing humans eyes to differentiate fake from real currency with simple tools like a UV light and a magnifying loup. http://www.officezilla.com/p-1012683679-royal_sovereign_rcd_2000_portable_4_way_counterfeit_detector.aspx?%22cagpspn=pla%22&gclid=COnMgdrz57kCFcvm7AodSE0A8A

The above device has a magnetic tape head attached to an op-amp for magnetic ink detection. 

The bill accept machine is much harder to fake out than a human.  It compares a pattern of photo diode readings from several tracks.  These are bills have ink illuminated with different colors that will be reflected, florescence, absorbed, or anti-stokes fluoresced.  Ink jet, xeroxed, or printed facillimallies will not react to light the same way as a real deal bill will.   This is hard to spoof.  It might be possible to spoof if you read the light sensor signals and play back the signals with a light source or a special reverse engineered fake bill. 

[loveman]

Old versions of bill accepters used a reference bank note to scan and compare against.  Xeroxed notes used to get through these until some tweaks were made.  These pre-dated cheap memory or cheap LEDs. 
The reference note and the test note were scanned and compared for similarity. 

The new units must have a very large signature repository.  These devices have to be forgiving enough for somewhat crumpled notes.

[guythepie]

The logo on the device is that of Mars Electronics International, a UK based manufacturer. A big player in coin-mechs etc.
The cable looks to be an MDB (Multi Drop Bus), widely used in vending machines. 9 bit, 9600 (if my memory is correct!). By default coin & bill acceptance is disabled until told otherwise by the vending machine. I vaguely recall that the specific note acceptance can be controlled by the vending machine too.
It's been years since I last worked on vending machines though... becoming a bit of a hazy memory these days...

[eliocor]

Where does this come from? Does not match my experimental data - see images below.

It depends on current passing trough the LED.
In general this measure is made with a 20mA current, but it is not so important: you have only to know that the shorter the wavelength, the higher the Forward Voltage.
It will be impossible that an IR LED will get a 3V Forward voltage, so it will be very easy to identify if it is an IR or UV LED.

BTW, when I make LED wavelength measurements, I use this spectrometer (about 0.1nm resolution in my configuration): you'll discover that changing temperature or forward current will shift the wavelength.

This effect is rather dramatic if you put your LED in liquid nitrogen:


in the second video you can see the Forward Voltage changing together with the wavelength!!

[ryanblace]

It appears the layout of the sensors allows the user to insert the bill upside down.  In the code, you just compare the sensors in reverse.

Also, the 45 degree sensor is reading the surface of the bill compared to reading through the bill for the outside sensors. I'm sure that was assumed, but I didn't hear it on the video.

I wouldn't be surprised if it doesn't actually read the signal for the entire bill as it goes by each sensor.  They could then teach it new bills at the factory by basically:
1) Tell it "here comes a good $1"
2) It scans the entire length (or some decent fraction of it)
3) Remembers what it saw.

Then when it is in the field, after reading a bill, it compares what it saw to what it wanted to see:

62% match to a $1 bill (right side up)
89% match to a $5 bill (right side up)
71% match to a $10 bill (right side up)
42% match to a $1 bill (upside down)
30% match to a $5 bill (upside down)
28% match to a $10 bill (upside down)


Must be a $5 bill.

16% match to a $1 bill (right side up)
24% match to a $5 bill (right side up)
36% match to a $10 bill (right side up)
etc

Must be Canadian bill, reject it.

[EEVblog]

Also, the 45 degree sensor is reading the surface of the bill compared to reading through the bill for the outside sensors. I'm sure that was assumed, but I didn't hear it on the video.

Of course. I might have forgotten to say that.
It's obvious the two inner sensors reflect back, but they would also likely go through the note and reflect back due the (non back) surface on the opposite side.

[mikeselectricstuff]

It seems unlikely to me that the note acceptor is using UV. Those photodiodes aren't going to detect UV at all -- the glass lenses will block it quite effectively.

That's only the case for shortwave UV.
It may be looking for fluorescence, so the detectors don't need to be UV sensitive (UV detectors are typically exotic and expensive, usually made bu Hamamatsu)

Also most UV LEDs I've seen are clear; the smoked plastic is generally reserved for infrared LEDs.

Agreed. A quick test for UV is some fluorescent material, e.g. a highlighter pen.
I doubt a video camera would have significant sensitivity at wavelengths below visible violet

[Stonent]

It seems unlikely to me that the note acceptor is using UV. Those photodiodes aren't going to detect UV at all -- the glass lenses will block it quite effectively.

That's only the case for shortwave UV.
It may be looking for fluorescence, so the detectors don't need to be UV sensitive (UV detectors are typically exotic and expensive, usually made bu Hamamatsu)

Also most UV LEDs I've seen are clear; the smoked plastic is generally reserved for infrared LEDs.

Agreed. A quick test for UV is some fluorescent material, e.g. a highlighter pen.
I doubt a video camera would have significant sensitivity at wavelengths below visible violet

Just reminded me of the video you made on separating the wavelengths of light. 

[eliocor]

It may be looking for fluorescence, so the detectors don't need to be UV sensitive (UV detectors are typically exotic and expensive, usually made bu Hamamatsu)

Once I disassembled a rather old French chip card reader (I believe used on ATMs before the advent of Euro):
the technique used for checking the compliance of the card was a VERY small wood lamp and three photodiodes, each one with a very narrow bandwidth optical filter.
I think the card was treated with one or more fluorescent dyes and only with the right combination of emissions it was accepted by the reader.
The reader was very small for its age and surely it wasn't cheap, due to narrowness of the filters.

I admit I have never checked my ATM/credit cards with UV light...

[mikepa]

I guess it must be enabled from the vending machine controller. When the machine is not working the acceptor should not accept notes.

That's exactly what's going on.  this makes sure your money doesn't get swallowed up by a machine that's empty or malfunctioning in some way or another. Otherwise these things are dead reliable electrically.  Their biggest issues as dave noted is that the mechanicals and optics get absolutely filthy. After you push maybe a thousand bills through it you need to just open the thing up clean off the feed belts and sensors and you're "money"

as an aside, these things aren't really about detecting counterfeits, there's really very little of that going on, but rather to make sure the bill is the right denomination.

Switch 6 at 5:10 seems to be enable/disable for host ready.

[Clear as mud]

When they did the major bill redesign in the late 90s they added color shifting ink. On some bills there was a logo and on some it was the treasury seal.  If tilted it alternates between green, gold and black.

The ink is a controlled ink, meaning they don't just sell it to anybody.  It is made in a European country (maybe Switzerland?) and sold to various governments for use in printing their currencies.

A number of years ago I did see a counterfeit bill that would pass the pen test.

The pen test is worthless for catching skilled counterfeiters.  The only thing those currency pens do is test the pH of the paper, which can be faked easily, not only by using a paper that won't absorb the ink (as you said), but also by impregnating any paper with a buffered solution of the proper pH.  It's much more reliable to look for the watermark, embedded strip, and color-changing ink than to use the marking pen.  There are two reasons the pens are used, despite being not very useful for detecting fake currency:

• Anyone can do it with minimal training.
• It can be done more surreptitiously, so the customer doesn't realize you are checking his bill for legitimacy.

[SeanB]

AFAIK the major producer of faked notes was the print presses used to make the Iraqui Dinar by the late lamented Saddam Hussein. He had the right presses, the right paper and the right inks, all supplied by the US treasury. All he needed was the plates, and he even had the right numbering indexers to serialise the notes.

Here the highest denomination is a R200 note, and they were all withdrawn recently and hurriedly replaced with a new design, as they discovered that they were being counterfeited in large numbers. The same with the R100 and the R50 notes. There have been a large number of fake coins as well, and they are pretty common and in circulation in large amounts. Some are plated steel, some are pot metal and some are pretty good. One was only found out by chance, there were complaints about the noise from the plant late at night, and then the plant was discovered. Had been in operation for a long time running 24/7 stamping out the coins in steel strip and then plating them in a bath.

[AG6QR]

The pen test is worthless for catching skilled counterfeiters.  The only thing those currency pens do is test the pH of the paper, which can be faked easily, not only by using a paper that won't absorb the ink (as you said), but also by impregnating any paper with a buffered solution of the proper pH.

Minor correction.  I believe most of the detector pens use a solution of iodine, which will react with the starch in wood-based paper.  It's not pH based.

http://en.wikipedia.org/wiki/Counterfeit_banknote_detection_pen

Agree totally on the uselessness of them, but they're easy to use and make people feel like they're doing something.  If I had a business that employed a lot of cashiers, I'd forget about the pens and just make sure every cashier had an easy way to backlight the bills and knew what a good bill looks like when backlit.  That's just as easy, and while not 100% perfect, I suspect it would catch more fakes than the pen would catch.

[G7PSK]

Don't bin that unit yet I have just posted a one and a five dollar bill of 2003 vintage along with a Sony E reader.

[Garywoo]

Old versions of bill accepters used a reference bank note to scan and compare against.  Xeroxed notes used to get through these until some tweaks were made.  These pre-dated cheap memory or cheap LEDs. 
The reference note and the test note were scanned and compared for similarity. 

The new units must have a very large signature repository.  These devices have to be forgiving enough for somewhat crumpled notes.

I wonder if they have variable limits of acceptance that can be changed depending on bill value, I imagine a $1 bill would have much more wear and tear than a $20 of similar age.

[kondy73]

Yes, it's quite likely it does some form of entire bill capture and then comparison with an existing scanned template.
Not sure at what points it would switch the red and IR leds though?

Hi David
I work in the gaming industry for 7 years and I can tell you that your assumptions are correct. Firmware can not accept the newer bills.
Why before disassembling, BV have tended reading bills, but after reassembling did not want?
This implies two things.
1) This model BV with these firmware accepts banknotes without an master machine. But exist are also firmwares and BV models which waiting to command for  the initialization eg. using RS232 or USB from master device.
2) after disassembling and reassembling sensors pcb´s probably occurred to change relative position of sensors, respectively some dust has moved away or disappeared, was added in lenses. It is enough that in the BV going mistuning settings (some older models are highly susceptible) are prone to it and need to do calibration using a calibration paper.

In principle, the job description of each BV is as follows.
After inserting banknotes is interrupted scanning beam (beams) and will start the bill transport motor. The motor speed are continuously monitored in real time to achieve, if possible, move step by step, somewhere is also used for this purpose also normal stepper motors.
At each step, the recorded image of the sensors stored in RAM.
They also tested the length of banknote.
The resulting image is compared with the template in a certain tolerance transverse position notes. The sensor records, some symbols inside the banknote using a beam that shines through the paper and some sensor is the reflective for colors testing on the surface .
Also used a magnetic sensor for sensing the metal strips in banknotes and in addition to infrared, red, green, blue and white beams are also used in the UV.

I think about I will send you some intelligent coin acceptor to you investigate if you would like, which can be programmed for any currency.
Henry

[iuliano666]

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[Fungus]

In principle, the job description of each BV is as follows.
After inserting banknotes is interrupted scanning beam (beams) and will start the bill transport motor. The motor speed are continuously monitored in real time to achieve, if possible, move step by step, somewhere is also used for this purpose also normal stepper motors.
At each step, the recorded image of the sensors stored in RAM.
They also tested the length of banknote.
The resulting image is compared with the template in a certain tolerance transverse position notes. The sensor records, some symbols inside the banknote using a beam that shines through the paper and some sensor is the reflective for colors testing on the surface .
Also used a magnetic sensor for sensing the metal strips in banknotes and in addition to infrared, red, green, blue and white beams are also used in the UV.

I'm always impressed when I see the speed of banknote readers in banks. They stick a huge wad of bills in there and it just goes 'brrrrrrrrrrrrr' and spits them out the other side as fast as the motor can go. How is is possible to do any kind of detailed checking at that speed?

I know that 1080p video can easily be compressed in real time so it makes sense that checking 2-3 banknotes per second should be perfectly possible, it's still impressive though.

They also have to work with dirty old banknotes and not be fooled by photocopies. A lot of that is down to the high resolution of the printing process (which is hard to reproduce), but still...it's clever stuff.

[boffin]

Pretty sure it didn't accept the $5 bill, because the DIP switch wasn't set to accept $5 bills 

Also the 4 pulse/1 pulse is because there's a lot of old vend (like video games) that are based on 25 cent pieces...

[economymachine]

The detector machines seem to be the better choice for detecting counterfeits. The Federal Reserves website acknowledges that detector pens have limitations -http://www.federalreserve.gov/faqs/currency_12597.htm

Here is also a post on the science of cointerfeit detection - http://www.itestcash.com/blogs/itest-university/29790081-the-science-of-counterfeit-money-detection

I'd imagine the companies making the bigger modeled machines would be doing it with technology to catch the more sophisticated bills with UV and infrared technologies.

[nitro2k01]

Dave did you ever get around to testing the newer bills someone sent you, with the device?