I don't want to make any destructive or non-reversible modifications to my MGA, so the controller needs to be integrated in the current factory configuration (with the stock DR2 wiper motor).
Also I don't want to change the dash wiper switch to a multi position switch or anything non factory, so I need to make use of the stock ON-OFF switch to control the wipers state (ON or OFF) as well as frequency (intermittent delay).
The wiper motor may pull 5 to 10amp so the system needs to be able to sustain more than that, ie. using a power relay to drive the motor.
The solution I thought of was to use a microcontroller to read and interpret the wiper switch ON-OFF sequence to activate and change the frequency :
- Pull the switch to activate the wipers at their slowest intermittent settings (wiping every 10sec for exemple).
- Push then pull the switch quickly to go to the next intermittent settings (wiping every 5 seconds)
- Push then pull the switch quickly again to go to the next intermittent settings (wiping every 3 seconds)
- Push then pull the switch quickly again to go to the last setting ie. continuous wiping.
- At any moment, push the switch for more than 2 seconds to turn off the wipers and reset reset the system, next switch activation will start the wipers at their slowest intermittent settings as described above.
I decided to use the Attiny85 microcontroller as it is easy to program (Arduino framework compatible), has enough I/O pins for reading the switch position and send pulse to the relay, has a built-in clock, is cheap and readily available.
It works with 5V so I also need to have a 12v to 5v converter on the board.
In short, the controller will sit right before the wiper motor, having the original 3 wires from the stock MGA harness connected to the controller, and 3 wires out from the controller to the wiper motor. The controller will have 3 main parts :
- 12V to 5V regulator
- Power relay