Simple MCU-less Differential Motor Drive Circuit

Posted on Feb 7, 2014

Originally, the tank cost around Php400 but then it was sold at around a hundred less. Without thinking twice I know I had a great offer so I decided to buy the toy. Opening the toy was quite a bit tricky. The track belt needs to be removed first and the middle wheels must be pulled out to reveal the two screws joining the tank`s upper body to the lower chassis. Inside it is a little circuit

Simple MCU-less Differential Motor Drive Circuit
Click here to download the full size of the above Circuit.

board centered around an SMT IC. Guess what it is, a microcontroller Eeeeeh! You`re wrong. It is controlled by a dual comparator IC which is pin to pin compatible with LM358 (the body marking says it`s 0358 ). Inside the gearbox are two small DC motor no bigger than a cellphone vibrator motor that differentially drive the tracked wheels and, of course, a couple of gears. Optical sensors are located at the bottom. The main part are the phototransistors (dark part) that detect the reflection (indication that the surface is not black) of the light emitted by the red LEDs (transparent part). The outputs of the comparator provide the drive signal to turn on/off the motors of the tank. It was easy to trace the circuit`s layout since few component resides on the circuit board. Looking at the circuit, we can clearly see a window comparator that turns either of the motor off when the voltage produced by the phototransistors divider network goes beyond the window voltages (most of the time phototransistors are shorted but it opens when it senses a black line).

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