This control board connects a microcontroller to the wheelchair's motor driver.
The motor driver moves the electric wheelchair, based on two control voltages. It seems, that those control voltages are used by several types of electric wheelchairs, although the level of the voltages differs from wheelchair model to wheelchair model.
One of the voltages is used for driving (5.3V=backwards, 6.0V=stop, 6.7V=forward), the other is used for steering (5.3V=left, 6.0V=straight, 6.7V=right). A third voltage is always on 6.0V level and it is used as reference. This board generates all those voltages. It also controls the "Totmann circuit" and powers up the motor driver. The inputs for this board come from a microcontroller (I used a picaxe 40x). The controller generates a PWM signal, which is flattened by capacitors. In a next step, the level of the flattened voltage is raised by a LMU324 opamp IC.
Please note, that the device on top left, which is described in the layout as "Song Chuan... whatever" , is the relay, which powers up the motor driver. It has to stand 24V and 1-2 amps. So better take a big one.

The yellow sponge beyond the emergency off, is my latest invention: a spirit cooling system. It turned out, that the 5V regulator got quite hot. At the moment, I don't know really why. There are just 200mA going through this device, and it should stand 7.5A. However, I've attached the sponge with some aluminum to the regulator. Then, I saturated it with spirit. If you decide to try the same - don't make me responsible for any unexpected disasters. And please have a fire extinguisher nearby.

(Several months later I found out, why it got hot. The voltage regulater was simply used in a very wrong way in this circuit. Read another related diary entry here.)

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