After a bit of research, I realized that the QRE1113 "Reflective Object Sensor" (Digital) that I had purchased for the line sensor would not work for my 1-bit robot. Although it is advertised as "Digital" it requires a microcontroller to charge up a small capacitor and time how long it takes to discharge - "the faster that capacitor discharges, the more reflective the surface is." What, what? Timing a discharging capacitor is not "Digital". I don't even know what that is... "temporal" maybe? The advantage is that you get a gradient input, and you would test for your cut-off (on vs off the line) in software. But there is no way I can do that with my 1-bit MC14500b processor. I could rewire the sensor to be the same as the analog version, then send the signal to a comparator circuit, but I really don't wnat to get bogged down in that during the short time I have dedicated to work on this.
Fortunately, I found a standard sensor board that includes the comparator circuit and will give me a nice adjustable "1 or 0" binary output (or analog if I want). It's certainly not era-appropriate, but the LM393 comparator circuit is probably not too different from what might have been used back in the day.
After getting new sensors ordered, I went to work on the output driver board. I basically copied a circuit I found online for driving small DC motors and duplicated it four times. I know I will need two drivers- one for each wheel, and maybe one more for the sound/light board, and I added a fourth just because it all looked so tidy that way. I still need to get a piece of metal for the heatsink, finalize the layout and get it soldered down. I used TIP110 transistors because they were cheaper and could handle more than enough current to drive the 1.5Amp max power (stalled) requirements of each motor. For a modern build, a MOSFET like the IRFZ44 would be better choice and would have an even simpler circuit. I bought some MOSFETs to test out and if I get this running I will make an interchangeable 'modern' driver board. Note the shrouded connector that will help orient the ribbon cables carrying 9V, 5V, GND and input signals. I also added some jumpers to select whether to use +5V or +9V output voltage.
Stay Tuned for some more thorough exposition and background once I start working on the MC14500b processor circuit.
Current Part List:
Chassis
- FEETECH Mini Round Robot Chassis Kit - 2WD with DC Motors
- 5x7cm Universal Breadboard Bakelite Test Prototype Boards for Electronics Experiments
- Misc. screws and nylon risers from my favorite store, Murphy's Surplus.
Input
Line Sensor Breakout - QRE1113 (Digital)- TCRT5000 IR Photoelectric Reflective Sensor
Output
- 4 x TIP110 Darlington Transistors
- 4 x 2.2K resistors
- 2x5pin shrouded header, Murphy's Surplus
- Single row straight pin header, cut to 4 pieces with 3 pins each
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