11 Jul 2006 Nic   » (Master)

July 10th, 2006

I finished soldering the interface circuit today. This circuit has 12 connection wires total. It has two power wires, three wires for the gas pedal potentiometer, three wires for the brake pedal potentiometer, one wire for reverse, and three wires (direction, high-side power, and low-side power (PWM)) to control the four H-bridge circuits. These last three have indicator lights soldered onto the board - a red LED for direction, a green LED connected to the PWM signal, and a yellow LED for high-side power. I tested the circuit on the H-bridge circuit I've built with one of the motors and it worked great.

This is a complicated little circuit. When generating a PWM signal, it must ignore the gas pedal position if the brakes are on. In addition to generating the PWM signal, this circuit has to give the motor controller a direction signal. This signal must be forward if the gas pedal is down and the car is going forward and backwards if the gas pedal is down and the car is in reverse, but in both situations it must be inverted if the brakes are on. It uses an XNOR gate (or snore gate as I like to call it) to accomplish this. It also has an output to turn the high- side MOSFETs in the H-bridge circuits on or off. They are on whenever the brakes are off and off when the brakes are on.

This is definitely one of my more-compact circuits. It's smaller than the voltage doubler circuit. With a total component count of 56 and dimensions of 2 1/8" x 1 1/4", there are approximately 21 components per square inch, and that's not including wires. Of the 286 holes in the perf- board, 211 of them have a component lead or wire through them. That's 74% of the holes that are used. Look at the pictures (http://www.craterfish.org/teamprodigies?pictures?2006/Jul) to see what I mean.

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