DIY Pulse splitter?

Tags: #<Tag:0x00007f6e10898ed0> #<Tag:0x00007f6e10898a70> #<Tag:0x00007f6e10898840> #<Tag:0x00007f6e1089ffa0>

I’d like to capture pulses from several water meters in a building on my college campus. The water meters provide a simple dry contact closure through a pair of wires but the wires are connected to a campus-wide data collection system (but this expensive system is mis-counting the pulses!). So I need a pulse splitter to provide a second output that I can capture on a Arduino-Pi setup. But I don’t want to spend money on a pulse splitter because I should be able to make one. My first choice would be a splitter like the Elster pulse splitter that uses dual Schottkey diodes according to its spec sheet. I get the general concept of using diodes but can’t quite figure out how to arrange the diodes to provide two separate independent outputs. Can anyone help?

Your big problem will be knowing whether you need galvanic isolation between the campus system and yours. Unless you know that you don’t, then you’ve probably got to assume that you do.

Without knowing exactly how the campus’s system works, it’s hard to guess what might be a viable system: my thoughts are directed towards a high sensitivity opto-coupler, either in parallel with the meter that you could drive from the voltage supplied to the meter contacts, or in series with the contacts that you drive with the current passing through. Either way, you don’t want to prevent their system from seeing the pulses. Then you can do as you normally would with the isolated opto-transistor output feeding into your Arduino.

Thanks Robert. Yes, I have been assuming that I need galvanic isolation. The opto-coupler approach is a good idea - I’ll look into it. At the same time, I am still intrigued by the diode-based pulse splitter. I’s become a puzzle that I need to figure out! If it provides isolation and just requires a couple of diodes, it could be even simpler and more compact than opto-couplers.

That’s a very neat trick if it’s true. My bet is it isn’t providing full isolation. It sounds as if it might just be a diode “OR” or “AND” gate - to prevent a back-feed from one system to the other.