Debouncing issues

Other Hardware Sensors
1

Hi all,

I'm using a reed switch to measure rotational speed and am trying to debounce the input. The problem that I am encountering is that at low speeds the bouncing is occurring at about 200ms. While at higher speeds the genuine input also occurs around 200ms. So if I set a debounce interval of 200ms then I cut off the high speed input.

Does anyone know of a way to debounce based on previous inputs. Seen as directly preceding a false input the time difference is large. Whereas a genuine high speed input is preceded by another high speed input.

E.g.
Low speed:
14:32:55.587 -> 2.25 dT / 26.69 RPM
14:32:58.967 -> 3.36 dT / 17.84 RPM
14:32:59.264 -> 0.30 dT / 196.73 RPM
14:33:02.886 -> 3.61 dT / 16.61 RPM

High speed:
09:34:41.115 -> 0.38 dT / 157.86 RPM
09:34:41.368 -> 0.24 dT / 248.67 RPM
09:34:41.664 -> 0.30 dT / 202.06 RPM
09:34:42.072 -> 0.38 dT / 156.53 RPM

2

Use a Hall sensor instead. It does not require debouncing at all.

3

As you've not provided any code it is impossible to see if there is an obvious problem with it.
Here is my solution to debouncing, but there are plenty of others: Buttons and other electro-mechanical inputs (introduction)

Also, if you are detecting the speed of a rotating shaft one solution might be to have 2 reed switches at 90 (or so) degrees to each other, and use their output as if from a rotary encoder. There is no need to debounce a rotary encoder provided you deal with the output from it using a state based approach.

4

I think the second option might be what I'm looking for, that or using a hall effect sensor. The debouncing code I have been using is similar to yours:

void rotation() {
  dT = ((micros() - last_micros)/1e6);
  if(dT >= debouncing_time / 1e3 && dt <= 10) {
    Serial.print(dT);
    Serial.println(" dT");
    last_micros = micros();
  }
}
5

That’s microseconds you have there not milliseconds …. Have another look at your timings , there is a limit to how fast a Reed switch can operate and it won’t bounce for 200mS ! 4mS is more like it ( 4000micro seconds)

Note also that the print statement takes time to process

6

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