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Improvements to the PWM Fan usermod #5015

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ea98f18
Fan: more precise RPM calculation
qistoph Oct 21, 2025
ed1c357
Fan: Show locked state when tacho is used
qistoph Oct 21, 2025
3ec1528
Fan: Lineair PWM control
qistoph Oct 21, 2025
44fab44
Fan: Disable lock from UI with speed: 0
qistoph Oct 21, 2025
a33de5d
Fan: fix code review issue
qistoph Oct 23, 2025
8c28def
Fan: fix code review issue
qistoph Oct 23, 2025
05bfebb
Fan: fix code review issues
qistoph Oct 23, 2025
44f96de
Revert "Fan: Disable lock from UI with speed: 0"
qistoph Oct 23, 2025
834556d
Fan: fix code review issues
qistoph Oct 23, 2025
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62 changes: 36 additions & 26 deletions usermods/PWM_fan/PWM_fan.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -54,23 +54,23 @@ class PWMFanUsermod : public Usermod {
int8_t tachoPin = TACHO_PIN;
int8_t pwmPin = PWM_PIN;
uint8_t tachoUpdateSec = 30;
float targetTemperature = 35.0;
float targetTemperature = 34.5;
float maxSpeedTemperature = 38;
uint8_t minPWMValuePct = 0;
uint8_t maxPWMValuePct = 100;
uint8_t numberOfInterrupsInOneSingleRotation = 2; // Number of interrupts ESP32 sees on tacho signal on a single fan rotation. All the fans I've seen trigger two interrups.
uint8_t pwmValuePct = 0;

// constant values
static const uint8_t _pwmMaxValue = 255;
static const uint8_t _pwmMaxStepCount = 7;
float _pwmTempStepSize = 0.5f;


// strings to reduce flash memory usage (used more than twice)
static const char _name[];
static const char _enabled[];
static const char _tachoPin[];
static const char _pwmPin[];
static const char _temperature[];
static const char _temperatureMax[];
static const char _tachoUpdateSec[];
static const char _minPWMValuePct[];
static const char _maxPWMValuePct[];
Expand All @@ -96,17 +96,15 @@ class PWMFanUsermod : public Usermod {
tachoPin = -1;
}

void updateTacho(void) {
// store milliseconds when tacho was measured the last time
msLastTachoMeasurement = millis();
void updateTacho(unsigned long msInterval) {
if (tachoPin < 0) return;

// start of tacho measurement
// detach interrupt while calculating rpm
detachInterrupt(digitalPinToInterrupt(tachoPin));
// calculate rpm
last_rpm = (counter_rpm * 60) / numberOfInterrupsInOneSingleRotation;
last_rpm /= tachoUpdateSec;
last_rpm = (last_rpm * 1000) / msInterval;
// reset counter
counter_rpm = 0;
// attach interrupt again
Expand Down Expand Up @@ -167,25 +165,30 @@ class PWMFanUsermod : public Usermod {

void setFanPWMbasedOnTemperature(void) {
float temp = getActualTemperature();
// dividing minPercent and maxPercent into equal pwmvalue sizes
int pwmStepSize = ((maxPWMValuePct - minPWMValuePct) * _pwmMaxValue) / (_pwmMaxStepCount*100);
int pwmStep = calculatePwmStep(temp - targetTemperature);
// minimum based on full speed - not entered MaxPercent
int pwmMinimumValue = (minPWMValuePct * _pwmMaxValue) / 100;
updateFanSpeed(pwmMinimumValue + pwmStep*pwmStepSize);
}

uint8_t calculatePwmStep(float diffTemp){
if ((diffTemp == NAN) || (diffTemp <= -100.0)) {
DEBUG_PRINTLN(F("WARNING: no temperature value available. Cannot do temperature control. Will set PWM fan to 255."));
return _pwmMaxStepCount;
int pwmMinValue = minPWMValuePct * _pwmMaxValue / 100;
int pwmMaxValue = maxPWMValuePct * _pwmMaxValue / 100;

if (pwmMaxValue <= pwmMinValue) {
updateFanSpeed(_pwmMaxValue); // fail safe: invalid config, run at max speed
return;
}
if(diffTemp <=0){
return 0;

int pwmRange = pwmMaxValue - pwmMinValue;


if (temp < targetTemperature) {
updateFanSpeed(pwmMinValue);
} else if(temp > maxSpeedTemperature) {
updateFanSpeed(pwmMaxValue);
} else {
if (maxSpeedTemperature <= targetTemperature) {
updateFanSpeed(pwmMaxValue); // fail safe: invalid config, run at max speed
return;
}
float speedFactor = (temp - targetTemperature) / (maxSpeedTemperature - targetTemperature); // 0 - 1
updateFanSpeed(speedFactor * pwmRange + pwmMinValue);
}
int calculatedStep = (diffTemp / _pwmTempStepSize)+1;
// anything greater than max stepcount gets max
return (uint8_t)min((int)_pwmMaxStepCount,calculatedStep);
}

public:
Expand Down Expand Up @@ -218,8 +221,11 @@ class PWMFanUsermod : public Usermod {
unsigned long now = millis();
if ((now - msLastTachoMeasurement) < (tachoUpdateSec * 1000)) return;

updateTacho();
updateTacho(now - msLastTachoMeasurement);
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@blazoncek blazoncek Oct 22, 2025

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That's bound to be roughly 30s due to the statement above.

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@qistoph qistoph Oct 23, 2025

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That assumes that the call is effectively called every 30s. It could throw off the result if this is not the case due to high load.

It's a little improvement to make the code more robust.

if (!lockFan) setFanPWMbasedOnTemperature();

// store milliseconds when tacho was measured the last time
msLastTachoMeasurement = now;
}

/*
Expand Down Expand Up @@ -257,7 +263,8 @@ class PWMFanUsermod : public Usermod {
JsonArray data = user.createNestedArray(F("Speed"));
if (tachoPin >= 0) {
data.add(last_rpm);
data.add(F("rpm"));
if (lockFan) data.add(F(" rpm (locked)"));
else data.add(F(" rpm (auto)"));
} else {
if (lockFan) data.add(F("locked"));
else data.add(F("auto"));
Expand Down Expand Up @@ -316,6 +323,7 @@ class PWMFanUsermod : public Usermod {
top[FPSTR(_tachoPin)] = tachoPin;
top[FPSTR(_tachoUpdateSec)] = tachoUpdateSec;
top[FPSTR(_temperature)] = targetTemperature;
top[FPSTR(_temperatureMax)] = maxSpeedTemperature;
top[FPSTR(_minPWMValuePct)] = minPWMValuePct;
top[FPSTR(_maxPWMValuePct)] = maxPWMValuePct;
top[FPSTR(_IRQperRotation)] = numberOfInterrupsInOneSingleRotation;
Expand Down Expand Up @@ -349,6 +357,7 @@ class PWMFanUsermod : public Usermod {
tachoUpdateSec = top[FPSTR(_tachoUpdateSec)] | tachoUpdateSec;
tachoUpdateSec = (uint8_t) max(1,(int)tachoUpdateSec); // bounds checking
targetTemperature = top[FPSTR(_temperature)] | targetTemperature;
maxSpeedTemperature = top[FPSTR(_temperatureMax)] | maxSpeedTemperature;
minPWMValuePct = top[FPSTR(_minPWMValuePct)] | minPWMValuePct;
minPWMValuePct = (uint8_t) min(100,max(0,(int)minPWMValuePct)); // bounds checking
maxPWMValuePct = top[FPSTR(_maxPWMValuePct)] | maxPWMValuePct;
Expand Down Expand Up @@ -395,6 +404,7 @@ const char PWMFanUsermod::_enabled[] PROGMEM = "enabled";
const char PWMFanUsermod::_tachoPin[] PROGMEM = "tacho-pin";
const char PWMFanUsermod::_pwmPin[] PROGMEM = "PWM-pin";
const char PWMFanUsermod::_temperature[] PROGMEM = "target-temp-C";
const char PWMFanUsermod::_temperatureMax[] PROGMEM = "max-temp-C";
const char PWMFanUsermod::_tachoUpdateSec[] PROGMEM = "tacho-update-s";
const char PWMFanUsermod::_minPWMValuePct[] PROGMEM = "min-PWM-percent";
const char PWMFanUsermod::_maxPWMValuePct[] PROGMEM = "max-PWM-percent";
Expand Down