Some of the essentials are now working together. The bill sensor, time delay, and trigger for the fast/slow mechanism are functional. The gearhead motor is designed for 24V but goes much too fast at that voltage, even with the 3:1 belt-drive reduction. I am running it on 5V, so I had to build a separate power supply for it.

I mocked up a fast/slow moving arm mechanism in the hopes that it will be useful in a rough idea for grabbing the bill as it comes out of the dollar bill acceptor and whipping it across to some sort of storage.

I found some plastic timing gears (with brass inserts and set screws) and toothed belts from Stock Drive Products (https://sdp-si.com/eStore/) which made it easy to drive the 10" wheel.








But the problem now is that the arm must return to the same spot each time it cycles and ideally it should only cycle once.

Since the idea is to have something interesting in the way of mechanical movement and flashing lights, a second circuit to drive these events is needed.

The 555 timer at the bottom of the board is a one-shot timer, taking its input from the second pole of the Double Pole Double Throw (DPDT) relay on the left. It controls the second relay which will eventually control the interesting (I hope) stuff that will happen.

Once the breadboard sensor circuit worked I used a protoboard to create a usable circuit. The relay will be used to switch 15VDC for the bill acceptor motor.

Bought a used dollar bill acceptor on ebay. The existing electronics incorporated a microprocessor to drive the two motors, one to pull in the bill and the other to push the bill out into a stacking box. I disassembled the acceptor and just used the roller mechanism that pulled in the bill. Since the existing sensor circuits were designed to determine that a valid dollar bill had been used, they were too complex for the simple task I had of accepting any old bill someone wanted to donate. Of course it wouldn't discriminate between money and any old piece of paper.

I used a circuit from a site devoted to model railroad electronics (http://home.cogeco.ca/~rpaisley4/PhotoDetectors.html) using an LM393 dual comparator. One comparator is used with a phototransistor to detect dark and the other is used as a delay. Since the sensor I used was located in the input side, I needed the delay to keep the motor running to pull the bill all the way through. A little experimentation with resistor and capacitor values in the delay circuit was needed.

The Idea

Create a donation box that will encourage visitors to the arts center to make a contribution. Something with lights and action when greenbacks are inserted into a slot. The goal is to make it so facinating that people would keep feeding money so they could see what happens.

It would be fun if a vending machine "bill acceptor" could be used. That could trigger the mechanical action.