Pulse Counting Causes Spurious Results on Measured Circuits

I’ve implemented pulse counting on my water meter but I’ve noticed when someone is using the water, you get spurious results in the measured circuits. IE the upstairs sockets will jump from 40w to a random high figure.
Just wandered if anybody has experienced this?


Unfortunately, as far as I know, none of the regulars here are mind readers. If you told us what equipment and which sketches etc you are using, somebody might be able to help.

lol OK fair enough

3x EmonTx’s with DiscreteSampling RFM12B sketch

Pulse input is using a 10K resister to pull the input down and a 100nf capacitor to stop the bounce on the reed switch.

Why a pull-down? The default sketch enables the internal pull-up resistor, so you are immediately making a voltage divider that is going to limit the voltage swing. But that does not immediately explain your problem.

Now how does “upstairs sockets” relate to something that I know about? Like an Input number?

The circuit I’m using is…

So you are taking the input up to 5 V. The absolute maximum input voltage according to the data sheet is Vcc + 0.5 V, which is 3.8 V. That is stressing the input protection, and it’s possible you have damaged or destroyed that input.

But you still haven’t answered the question. I can’t help further until you do.

The reason for the 5 volts was the info provided in the building blocks.
I’ll wire it up to the 3.3 v output, that might be why I’m getting the odd random values when its pulsing.


The Building Blocks example is using an Arduino, not an emonTx. The Arduino Vcc is 5 V, the emonTx Vcc is 3.3 V.

Ahhh I did not know that.
I think it might be a good idea for the documentation to be updated to reflect hardware changes and identify potential damage to boards as everybody that asks the basic questions on the forums are promptly sent off to read and digest the supplied documentation within the building blocks, as they should, but the information needs to be clear for a novice to understand what’s relevant to the shiny new bits they’ve bought from the shop.
Not a dig at anybody but just providing feedback.


Did not the presence of both 5 V and 3.3 V on the terminal block alert you?

Most of Building Blocks is aimed at explaining the fundamental principles and the general background theory, and as such the examples using the Arduino are just that: examples. Indeed, many beginners still use Arduinos and prototype boards to construct their own energy monitor, and for them Building Blocks is (hopefully) a useful and valuable resource. But it must not be confused with the fully engineered emonTx and the specific application sketches for the emon series of hardware, even though Building Blocks is also used as the vehicle for explaining some of the very advanced concepts found there.