I'm playing with the power window circuit of a 1994 Volkswagen Golf III, to drive its 12v DC motor using my arduino mega.
The VW Golf high level wiring diagrams can be read here, on page 35, but I couldn't find the datasheet of both chips on the driver board (I know, useless picture, but it was the best I could get out of my cell phone)
The chips are:
- a Microchip "FHS03 00129" "6D56G" "LLNB9610"
- an unknown manufacturer's "9614VGC" "6 66 30" "00080"
According to what I could understand from the wiring diagram here's how I connected the 12v battery, a 5v source that mimics what the arduino would eventually supply, and the board connector:
- Now, when I connect the battery terminals only to the wires number 1 and 15, the motor is still, as expected (needs "enable" and "direction").
- When I let the direction wire (number 11) touch the USB port positive or negative pole, the motor is still as expected (needs "enable").
- Then I let the hotkey wire (black/yellow, number 7) touch the 5 volts from a computer usb port with common ground with the battery (something that sounds like "I turn the key on on the car"), the motor is still as expected (needs "direction").
- Now (it doesn't matter whether I keep the hotkey wire connected to 5v or not), if I let the direction wire touch the 5 volts positive pole the motor turns clockwise, and when I disconnect the direction wire the motor gets still, as expected.
- If I let the direction wire touch the negative pole, the motor turns anticlockwise, as expected, but it doesn't alwasy stop when I disconnect the wire from the negative pole, sometimes it keeps running, sometimes it stops. When it keeps running, it will stop if I let the direction wire touch the 5 volts.
Now I'd like to connect an arduino pin in place of the 5 volts usb cable, to feed the voltage needed to the direction wire (I just hope the motor will reliably stop from the anticlockwise position feeding it 5 volts for a short period of time), my question is: what it's best to do to protect the arduino in this scenario ? should I be using a diod to prevent current flowing backwards from the motor on the pin wire (it might be something the chips on the board are already there for, but since I can't get their datasheets I'll never know), or should I do something else ?
thanks and best regards,