Fan delay and advance timing

AulaStud_fridge_compressor_timer_controller.ino

@@ -1,29 +1,54 @@
-int disable = 0;
-int timer = 0;
-int timerMAX = 900; //(countdown in seconds)
-int fan = 0;
-int relayPin = 0;
-int fanPin = 1;
+// Hi! Barb here: this is a quick and dirty implementation of a refrigeration compressor + evaporator fan(s) controller.
+// 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
+// control panel. This code relies on an external thermostat already doing its work and is not meant to manage internal
+// temperature. It is written to make sure the compressor can get a minimum rest-time between cycles as to not overheat.
+// This relay and attiny are connected in series with the main thermost's relay, so that they only function when it's calling.
+// With this in mind, we assume the thermostat has just called for cooling every time the attiny is booted and leave the
+// compressor running. After a set period of s (timerMAX) the compressor is switched off.
+// In order to aid thermal transfer and maximize COP while using butane as refrigerant, the system needs to have a higher
+// average temperature. Due to this reason, a fan is fitted between the fridge and freezer compartments to move air between
+// the two. The fan is turned on after fanStartDelay to prevent rapid heating of the freezer and turned back on when the
+// timer hits fanStopAdvance to allow for further freezer sub-cooling.
+
+// Last updated: 05/03/24
+
+bool disable = 0;               // bool to store compressor disable status
+int timer = 0;                  // active countdown timer, between timerMax and 0
+const int timerMAX = 1500;      // (countdown in seconds)
+int relayPin = 0;               // compressor relay output pin (active LOW)
+int fanPin = 1;                 // fan MOSFET output pin (active HIGH)
+const int fanStartDelay = 60;   // fan turn-on delay in seconds
+const int fanStopAdvance = 30;  // fan turn-off advance in seconds (before the compressor stops, allows to sub-cool the freezer)
 
 void setup() {
   // put your setup code here, to run once:
+
+  // firstly, we initialize the needed outputs
   pinMode(relayPin, OUTPUT);
   pinMode(fanPin, OUTPUT);
+  // then we set them low to keep the compressor on and the fans off at boot
   digitalWrite(relayPin, LOW);
   digitalWrite(fanPin, LOW);
+  // lastly, we set the timer at maximum so that the loop starts counting down
   timer = timerMAX;
 }
 
 void loop() {
   // put your main code here, to run repeatedly:
 
+  // fan control logic:
   // only enable fans after the compressor has been running for a while
-  if (timer < (timerMAX*4/5) && disable == 0) {
+  if (timer == (timerMAX - fanStartDelay) && disable == 0) {
+    // enable fan(s) after set delay if the compressor is not disabled
     digitalWrite(fanPin, HIGH);
   }
-  else if (timer == timerMAX) {
+  else if (timer == fanStopAdvance && disable == 0) {
+    // disable when we are about to stop the compressor
     digitalWrite(fanPin, LOW);
   }
+  else {
+    // do nothing
+  }
 
   // compressor control logic
   if (timer > 0 && disable == 0) {
@@ -32,7 +57,7 @@ void loop() {
   }
   
   else if (timer > 0 && disable == 1) {
-    // when compressor is off, countdown moves at 5s/cycle
+    // when compressor is off, countdown moves at (1/5)s/cycle (5 times faster!)
     timer = timer - 5;
   }
   
@@ -40,7 +65,7 @@ void loop() {
     // reset countdown timer to max once 0 is reached
     timer = timerMAX;
     
-    // realy control logic: warning! LOW = active!
+    // relay control logic: warning! LOW = active!
     if (disable == 0) {
       disable = 1;
       digitalWrite(relayPin, HIGH);
@@ -51,10 +76,14 @@ void loop() {
     }
   }
   
-  else { //protect against underflow or bitflip
+  else {
+    // protect against underflow or bitflip: if no condition applies, reset to safe values
     timer = 0;
-    disable = 1;
+    disable = 0;
+    digitalWrite(fanPin, LOW);
   }
-
+  
+  // now wait 1s so that we can roughly count time using the timer variable
+  // this is a stopping delay, kinda bad, but we don't have any inputs, hence it shouldn't matter!
   delay(1000);
 }

AulaStud_fridge_compressor_timer_controller.ino.tiny8.hex

@@ -0,0 +1,53 @@
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README.md

@@ -1,3 +1,7 @@
-Controller basato su attiny45, un relé e un FET per il frigorifero usato che abbiamo preso per l'aulastud nel '23.
+Controller basato su attiny45 (bootloader flashato a 1 MHz), un relé e un FET per il frigorifero usato che abbiamo preso per l'aulastud nel '23.
 Abbiamo dovuto sostituire il termostato e il design dell'evaporatore (parte fredda della serpentina) fa sì che ci sia rischio di trasporto di olio dal compressore e che si intasi il sistema se il compressore lavora per troppi minuti di fila (tipicamente dopo 30 minuti, a quel punto tocca staccare il frigo, riscaldarlo con un phon per sturare il blocco di olio, di solito nel reparto freezer, e poi riaccenderlo).
-Questo controller è montato DOPO il termostato, in modo da impostare dei limiti di tempo massimo di accensione (15') e minimo di stand-by (3') del compressore. Inoltre, si occupa di accendere delle ventole nel compartimento freezer e frigo che aumentano il COP e permettono la completa evaporazione del refrigerante (butano).
+Questo controller è montato DOPO il termostato, in modo da impostare dei limiti di tempo massimo di accensione (15') e minimo di stand-by (3') del compressore. Inoltre, si occupa di accendere delle ventole nel compartimento freezer e frigo che aumentano il COP e permettono la completa evaporazione del refrigerante (butano).
+
+UPDATE 03/'24:
+Ho aggiunto un delay di 60s all'accensione delle ventole per permettere al freezer di pre-raffreddarsi e poi uno spegnimento delle stesse 30s prima del compressore per far calare ulteriormente la temperatura nel comparto freezer.
+Ho aumentato il tempo totale di accensione a 1500s (25'), portando il tempo di spegnimento forzato a 1/5 (5' con l'impostazione corrente)