Thursday, February 14, 2013

Programmable Fridge Timer

Somewhere in February of 2013, my dad ask me to build him a timer for fridge, that turns on 3 times a day, i.e. 1 hour on, 7 hours off. The fridge temperature regulating mechanism failed, causing it to run entire day, consuming too much energy and money.

Get excited, I surveyed online for small PIC microcontroller. After all ordered component arrived, I kickstart the project quick. :)

I'm using cheap PIC10F220 6-pin mcu and 40A automotive relay for the project. Most of the circuit are for power supply and relay triggering.

The relay contacts are equipped with capacitive snubber for arc-suppression, enhancing relay's life.

Firmware is coded with XC8 compiller in MPLABX, running forever-loop of delays.

The 3 lower GPIO used for driving the relay, the relay-status LED, and running-LED.
It comes with power-up 3 seconds delay.

Designing component layout.

Done, but untested.

And it works! :) 

The white LED for running-indicator, it blinks every second, for 500ms. The green LED for relay status indicator.

Fully enclosed, and running, notice the reset button, tied to the PIC MCLR.

Final result, with 12 inches connect cable.

It feels good when you could lighten your dad's burden, it may not much, but it's more than nothing. ;)  

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