PWM ledCWrite(255) or ledcWrite(1023) is not 100% on

[hallard]

Hardware:

Board: ESP32

Description:

Unable to light off PWM common anode RGB Led when setting value to latest value of range.

Old known issue of ESP8266 #5957 and now seen is Tasmota and my sample test program

The fix is described in comments of official sample code

But from logical working, having value going from 0 to 255 should means that 255 is full scale so always 1 and not having a little pulse. This does now works on ESP8266 with analogWrite(255) and comments have been updated to code according in this PR

// Per the Arduino docs at https://www.arduino.cc/reference/en/language/functions/analog-io/analogwrite/
// val: the duty cycle: between 0 (always off) and 255 (always on).
// So if val = 0 we have digitalWrite(LOW), if we have val==range we have digitalWrite(HIGH)

I know it's not arduino but I think if PWM could work as is 0 (always off) and max range value (always on) would be less confusing

my ledOff()sample function with 256 does works, but should works with 255, much easier if we use an uint8_t as scale range.

void ledOff() {
  ledcWrite(LED_RED_CHAN, 256);
  ledcWrite(LED_GRN_CHAN, 256);
  ledcWrite(LED_BLU_CHAN, 256);
}

[lbernstone]

esp32 does not have a fixed bit width like atmel and esp8266 boards, so max is pow(2,bit_res). You have not included your ledcSetup call, so your issue is not clear.

[hallard]

Yeah sorry about that, what I mean is that the bug is there if I call ledcWrite() with the max value of resolution

  ledcAttachPin(LED_RED_PIN, LED_RED_CHAN); // assign RGB led pins to channels
  ledcAttachPin(LED_GRN_PIN, LED_GRN_CHAN);
  ledcAttachPin(LED_BLU_PIN, LED_BLU_CHAN);
  
  // Initialize channels 
  ledcSetup(LED_RED_CHAN, 12000, 8); // 12 kHz PWM, 8-bit resolution
  ledcSetup(LED_GRN_CHAN, 12000, 8);
  ledcSetup(LED_BLU_CHAN, 12000, 8);

So 8 bits max value 255 does not light off the Led, 10bits max value 1023 does not light off led, I need to set to max value + 1 to get it working.
So in case of uint8_t (example) moving to all scope from 0 to 255 led will never go off.
In case of 10bits, same things set all bits to 1 (0x3FF) never light off the led

[me-no-dev]

255 is max light and 0 is off

[hallard]

yeah that is the issue (255) is not full 100% HIGH level, if you connect the LED as follow (3V3 not 5V of course)

You won't be able to light off the LED because 255 is not fully 100%

Detailled explanation, same issue than this one
esp8266/Arduino#5957

Of course if you connect the LED other side

your eye is unable to see light difference to full light and missing 1/255 pulse.

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