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89 lines
3.7 KiB
89 lines
3.7 KiB
// Hi! Barb here: this is a quick and dirty implementation of a refrigeration compressor + evaporator fan(s) controller.
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// I wrote this code to run it on an attiny45 that I was able to solder on the back of a 5V relay inside the refrigerator's
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// control panel. This code relies on an external thermostat already doing its work and is not meant to manage internal
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// temperature. It is written to make sure the compressor can get a minimum rest-time between cycles as to not overheat.
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// This relay and attiny are connected in series with the main thermost's relay, so that they only function when it's calling.
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// With this in mind, we assume the thermostat has just called for cooling every time the attiny is booted and leave the
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// compressor running. After a set period of s (timerMAX) the compressor is switched off.
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// In order to aid thermal transfer and maximize COP while using butane as refrigerant, the system needs to have a higher
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// average temperature. Due to this reason, a fan is fitted between the fridge and freezer compartments to move air between
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// the two. The fan is turned on after fanStartDelay to prevent rapid heating of the freezer and turned back on when the
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// timer hits fanStopAdvance to allow for further freezer sub-cooling.
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// Last updated: 05/03/24
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bool disable = 0; // bool to store compressor disable status
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int timer = 0; // active countdown timer, between timerMax and 0
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const int timerMAX = 1500; // (countdown in seconds)
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int relayPin = 0; // compressor relay output pin (active LOW)
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int fanPin = 1; // fan MOSFET output pin (active HIGH)
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const int fanStartDelay = 60; // fan turn-on delay in seconds
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const int fanStopAdvance = 30; // fan turn-off advance in seconds (before the compressor stops, allows to sub-cool the freezer)
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void setup() {
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// put your setup code here, to run once:
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// firstly, we initialize the needed outputs
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pinMode(relayPin, OUTPUT);
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pinMode(fanPin, OUTPUT);
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// then we set them low to keep the compressor on and the fans off at boot
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digitalWrite(relayPin, LOW);
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digitalWrite(fanPin, LOW);
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// lastly, we set the timer at maximum so that the loop starts counting down
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timer = timerMAX;
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}
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void loop() {
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// put your main code here, to run repeatedly:
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// fan control logic:
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// only enable fans after the compressor has been running for a while
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if (timer == (timerMAX - fanStartDelay) && disable == 0) {
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// enable fan(s) after set delay if the compressor is not disabled
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digitalWrite(fanPin, HIGH);
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}
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else if (timer == fanStopAdvance && disable == 0) {
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// disable when we are about to stop the compressor
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digitalWrite(fanPin, LOW);
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}
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else {
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// do nothing
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}
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// compressor control logic
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if (timer > 0 && disable == 0) {
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// when compressor is active, countdown moves at 1s/cycle
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timer--;
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}
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else if (timer > 0 && disable == 1) {
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// when compressor is off, countdown moves at (1/5)s/cycle (5 times faster!)
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timer = timer - 5;
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}
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else if (timer == 0) {
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// reset countdown timer to max once 0 is reached
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timer = timerMAX;
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// relay control logic: warning! LOW = active!
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if (disable == 0) {
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disable = 1;
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digitalWrite(relayPin, HIGH);
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}
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else if (disable == 1) {
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disable = 0;
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digitalWrite(relayPin, LOW);
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}
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}
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else {
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// protect against underflow or bitflip: if no condition applies, reset to safe values
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timer = 0;
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disable = 0;
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digitalWrite(fanPin, LOW);
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}
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// now wait 1s so that we can roughly count time using the timer variable
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// this is a stopping delay, kinda bad, but we don't have any inputs, hence it shouldn't matter!
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delay(1000);
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}
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