Reading a 3V pulse with the Flukso v2

I'm trying to read a pulse from an energy meter, which has an 'extra' module installed which apparently sends out a modulated pulse. Accessing the actual meter is not possible, due to the sealed box its placed in. (The seal is placed by the power company)

When trying to measure the output of this module, my digital multimeter registered 3V per pulse. As it is quite a slow one, and the pulse is pretty short, i'm guessing the actual value would be around 3.3V

Now, my question is; will this pulse signal be useful to wire to port 4 or 5, without breaking the thing?
I know from experience that these ports normally expect a shorted signal per pulse, as I've already hooked up the gas meter with a reed relais.

A solution for bypassing the 3V pulse is adding another relais that switches and shorts port 4 on each pulse... But if I can avoid this extra work, that would be great:)


icarus75's picture

Hi Gerben,

The FLM's pulse ports are indeed designed to be compatible with an open-collector type sensor output. The + pin is connected to the internal 5V rail through a 30kOhm pull-up. A 'pulse' will be triggered by a high-to-low transition on the input, i.e. shorting the + and - inputs.

Driving this input with an 'active' pulse should not cause any harm to the FLM. If the pulse voltage is indeed 3.3V then the FLM should detect the state changes as well. There is a difference in pulse logic. With an open-collector setup, a 'zero' is 5V and a 'one' is 0V. So pulses will be detected at the end of the pulse (3.3V -> 0V transition).

All-in-all, I think this should work, providing the pulse generator can sink current and that the voltage level is 3.3V. The best way to find out is to try.