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Controller requirements and basic function

A project log for Classic car intermittent wiper motor controller

Reversible, no extra switch, multiple frequencies delay module for classic British cars.

Frederic LFrederic L 10/31/2020 at 08:440 Comments

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 :

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 :

  1. 12V to 5V regulator
  2. Microcontroller
  3. Power relay

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