Dollar Bill Changer Photo Overview

Excerpt from http://money.howstuffworks.com/question269.htm

Creating a good bill changer is a tough problem.  The device has to work with all sorts of bills, from crisp new ones to ragged old ones, and it has to be reasonably good at telling real bills from fakes.  In many cases, the changer also has to be able to sense the denomination of the bill.  In order to accomplish these tasks, dollar bill changers use a variety of technologies.  Several different patents listed below discuss techniques that people have employed.  Some of these techniques have changed over the years as microprocessors have allowed more capability in the device.

Here are several of the techniques that have been tried:

A good bill changer will use several of these techniques because people seem to have a very strong desire to outwit bill changers.  If you read the patents listed below, you will find that they handle such things as people inserting just half of the bill, people inserting bills with strings attached so they can jerk them back out, people who try unplugging the machine with the bill half-inserted...

Here are some good patents to study:

Front panel overview.  This particular device was made by Mars Electronics.

Side view.  Not sure what it plugged into.

Rear view.  That is where the dollar bills are stacked.

Other side view.

Front plastic panel is removed.

Close up of the dollar bill insertion area with the front panel removed.  The red plastic must act as some sort of filter.

Power supply.  Nothing too fancy.  Provides both +15 VDC and +5 VDC.  Has a non-resetable fuse in the power line.  This was probably done so you'll have to call an expensive repair service if the fuse ever blows.  Or, you can fix it yourself for about 25 cents.

Motor on top of the changer.  This controls some little wheels and "rubber bands" which draw the dollar bill in at a fixed speed.

Close up side view.  Bill insertion is from the left.  Note the IR sensor (white plastic rectangle on left).  You can also see how the wheels draw the bill into the changer.

Alternate view of the insertion area.

Top view of the changer, looking down.

Bill stacking area with the power supply removed.

Rear view of the bill insertion area.  The magnetic ink sensor mounted in the middle is made by Nortronics, it is marked "M34502."

Internal view of the bill insertion area.  Bill insertion is on the right.  Note the series of LEDs (IR or UV?) under the plastic and the magnetic ink sensor in the middle.

Alternate view.  The little black feet trigger an optocoupler.

Bottom plate view.  Bill insertion is from the top.

Top plate view.  Bill insertion is from the top.

Bill insertion drive assembly.  It's like a little tank.

Top plate electronics overview.  Bill insertion is from the bottom.

Top plate separated from its plastic housing.

Top plate housing close up photo.

Top plate electronics.  The magnetic ink sensor is on the bottom.  It it just like a big tape recorder head.  The two encapsulated IR LEDs (toward the middle) are Vishay TSTA7100.  The black C-shaped object is an optocoupler.  I think the other LEDs are just regular IR LEDs.  Not sure what they do.

Top plate electronics, side view.

Top plate electronics, alternate bottom view.

Bottom plate electronics overview.

Bottom plate separated from its wheel assembly.

Bottom plate separated from its plastic housing.  Bill insertion is from the top.

Bottom plate electronics close up.  The two encapsulated devices toward the middle are marked Vishay TFKPBX43.  These part numbers don't show up in their catalog.

Bottom plate housing close up photo.