EEVblog #525 - Bank Note Acceptor Teardown

[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!