Pulse Count Sensor Wiring

I’ve got an older emonTx v3.2, which doesn’t have an RJ-45 jack.

I want to connect a pulse counter sensor but don’t want to cut off the nice moulded RJ-45.

I’m going to use an RJ-45 socket (from a faceplate) to wire it in, but i’m not seeing the wiring of the sensor anywhere - can anyone point me in the right direction?



I used one of these when I wired a pulse sensor directly to an RPi

Ah those are cool - though a little pricey for what they are!

Just found this:

Is the pulse sensor wired to pins 2 (5v), 5 (GND) and 7?



1 Like

Aha, this: says:

Pin 2 = VCC
Pin 5 = GND
Pin 6 = IRQ1
1 Like


From where?

Got this working!

It is pins 2, 5 & 6 as above.

I got one of those adapters from Amazon that @borpin linked to.

I wired Pin 2 to 3.3v, Pin 5 to GND and Pin 6 to IRQ 0 / Dig 2 - all on the screw terminals on the emonTx v3.2.

Because the v3.2 uses IRQ 0 / Dig 2 instead of IRQ 1 / Dig 3 on the v3.4, I had to change the following in the EmonTxV3CM sketch:


EmonLibCM_setPulsePin(3, 1);


EmonLibCM_setPulsePin(2, 0);


Whilst that would ordinarily be both advisable and sensible! It has however been noted that the sensor works better at 5v even when hooked up to a 3.3v IO, either (or both?) the emonPi or emonTx are wired 5v by design despite the MCU on both working at 3.3V.

Thanks for the heads up! - it seems to be working ok, but i’ll swap it to 5v to be sure!



On reflection, it might be worth hanging on for Robert to comment/confirm. He has done some testing of the output from these sensors, whilst I know what I’ve stated to be true of the emonTx/Pi etc, I do not know for sure that the RFu is as tolerant as the later devices (or even if it is a concern).

If it works ok, run with it? If you have issues I would put money on it being either the supply voltage or (sorry to say) the RJ45, they are renowned for issues with the temp sensors, I fully relate to not wanting to cut off the RJ45, but it’s certainly the place to look if you get odd readings, even if you get too many pulses counted.

There are details (as best we can extract from measurements plus one that was disassembled) here:

I’m using the optical sensor on an emonPi at the moment, and it’s certainly susceptible to a fluorescent light (with a glow-tube starter) nearby being switched on, to the extent of tens of pulses if the pulse repetition period is set to zero. A few days ago, it saw 18 kW in one 10 s interval - the c.t. saw 154 W.

1 Like

Ahh! that’s where it is, I’ve just been searching learn and resources and the wiki without any joy, I knew you had posted details but I had no idea where :slight_smile:

Nor me! But my private crib sheet did. :wink:

Ah interesting, My meter is in the garage with a number of fluorescent tube lights. I had a look at how my pulse sensor wired to the Pi directly and using the PulseInterfacer behaved. Looks like nothing out of the ordinary is reported.

Mine is in an understairs cupboard, which normally has the door shut - so hopefully it should be quite reliable.