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This is the schematic for the motor logic board. Controlling 3 motors and 2 relays, plus providing for position feedback, all through an 8 wire cable, required reducing the motor control signals to 1 wire to select the motor and 1 wire for motor direction. This requires 3 level logic, low, mid, high. Since TTL chips call a 1 volt level "high", I was able to separate mid and high by using an LED. On the input lines, the lower gates see a high if the input line is from 1 volt to 5 volts. The upper gate, since its input is through an LED, needs over 3 volts for high. The lower gate output goes low with an input of between 1 and 3 volts. At 3 volts, the upper gate output goes low, causing the lower gate output to go high. When the input wire is below 1 volt both left gate outputs are high, so the output of the gate to the right is low. So for 3 levels on an input wire there are 3 separate low outputs. On the right side of the schematic a low on a select gate and a low on a direction gate are combined to make a high on a motor drive wire. Since there is no mid signal decoded in the motor direction cluster, as long as the direction wire is at mid the motors are off.

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