EEVblog #525 - Bank Note Acceptor Teardown

[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Here the highest denomination is a R200 note, and they were all withdrawn recently and hurriedly replaced with a new design, as they discovered that they were being counterfeited in large numbers.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]

NOTE: This message has been deleted by the forum moderator Simon for being against the forum rules and/or at the discretion of the moderator as being in the best interests of the forum community and the nature of the thread.
If you believe this to be in error, please contact the moderator involved.
An optional additional explanation is:

[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?