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Project Help and Ideas » Car defrost button circuit replacement
September 19, 2015 by scootergarrett |
The rear defrost circuit in my POS car never seemed to work correctly, I tested the button and the relay and found nothing. The button to turn on/off the defrost is a momentary contact button that some how latches; there was no way I was going to be able to find and trouble shoot that circuit so I decided to completely bypass it. I ran a new wire from relay through the fire wall to behind the dash, controlling this signal controls the defrost. I initially tried making a completely analog circuit, but the bouncing of the signal from the input button was killing me. I then decided that the ATtiny85 would be a good solution. What I wanted the MCU to do was: 1) When circuit is power up (turning on car) have the rear defrost off 2) If button is pressed switch state of the defrost signal, and switch the light on the button. 3) If the button is held down (~2sec) enter a timed mode where the defrost will turn off after a set amount of time (~5min) 3a) Show that the button has been held for long enough by blinking light on button until buttton released The MCU has one input from the button, and two outputs that go to the relay and the light inside the button. A lot of the code is getting the 3rd task to work correctly and to de-bounce the button.
Here are some pics of the complete project board and the circuit diagram. I hope no one ever owns this car after me. Just another little project. |
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September 21, 2015 by JKITSON |
Scooter... Neat idea. I have an old clunker with similar problem. Thanks for documenting the project & code. This will make it much easier for me to try & fix my car. The schematic really helps. Thanks again for a nice project JIm |
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