Success came about 4pm last night, when I finally managed to get my stripped down electric wheelchair not only moving forwards, but also backwards under control of the PIC microcontroller.

Today I took it for a walk around the garden on a log serial lead. Perhaps I should call it Fido?

So what do we have? We start off with a small Visual C++ app which reads a standard PC joystick, and sends the values read as a string down COM1 serial port. A PIC24F 16 bit microcontroller mounted on an Explorer 16 demo board receives that data, does a quick calculation to turn speed and steering information into differential speed and direction data, and uses this to control the duty cycle of two PWM outputs and matching digital outputs for direction.

The PWM output for each wheel is fed into a 4QD VTX-40 motor controller - the direction signal is amplified by a transistor and fed in place of the reverse switch.

The rest is the original wheelchair - two 12V batteries feeding 24V to the controllers, and two geared 24V DC motors.

Next step - replace RS232 wired communications with ethernet, and get this going over wifi so the vehicle is literally wireless.