OpenEnergyMonitor Community

LED Pulse Sensor Maximum Imp/Sec


I am thinking of purchasing an Optical Utility Meter LED Pulse Sensor (possibly with an emonPi).
However, I can’t find an estimate of the maximum imp/sec which the sensor can detect, sorry if I have overlooked this.
Does anyone have experience with this sensor and higher Imp/Sec (70+imp/sec)? If so, any idea of the maximum pulse detection speed which is possible?

Best regards,


Welcome, @Habanero , to the OEM forum.

Basically - we don’t know, because the only substantive data is that which we’ve found out by dismantling a unit and reverse engineering it. You can find what we know here: First try with EmonPi - Pulsecount stuck at 1 - #16 by Robert.Wall
Also Adjusting sensitivity of Optical Pulse Sensor - #21 by Kempson

The sensor is a photodiode, speed will not be a problem for that, nor for the transistor circuitry (at least, not at the 70 Hz sort of speed you mention). The problem will be in whatever you are using for counting the pulses. If you will be using an emonTx or an emonPi, then the pulse counting is interrupt-based, but the processor is doing other things as well as counting pulses, and interrupts are of necessity turned off for short periods. I seem to remember testing the sensor by flashing a LED under software control, but I cannot find a record of the result.

I have a feeling that 70 Hz might be possible - but no evidence to support that. Again, if you are using an emonTx or an emonPi, the standard software incorporates an anti-contact bounce delay that means it refuses to count at faster than about 8 Hz, so that will need changing.

Thanks @Robert.Wall, that is interesting.

Regarding the anti-contact bounce delay limiting to 8 Hz, why is this implemented?

Exactly that - anti-contact bounce! - for when you use something with mechanical contacts.