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I have sourced an LPG consumption meter from China with pulse output. I am looking to hook the output up to an arduino to get the consumption metrics. Unfortunately there is not too much documentation available on the unit that I can find. The suppliers inform me that:

  1. Black wire(signal 1)
  2. Black wire(signal 2)
  3. Red wire(earth wire)

So that's a start, I know the unit pulses a signal for every cubic meter of gas consumed. What I'm wanting to know is:

  1. What are the input [likely] voltages for the unit (or how could I establish this)?
  2. How do I wire the unit to an arduino?
  3. I can cook up a sketch to do the reading but what is the signal I am looking for?

The mechanical meter itself has a metallic strip on the 0 digit of the wheel (how it achieves the pulsing itself no doubt) so another approach would be something like this which is a more accurate option. For this option any suggestions on what photoreflectors are available for the Arduino which could do the job.

meter output wiring - one red two black

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Do you have a link to the gas meter documentation or the name of the meter? – Cybergibbons Mar 7 '14 at 8:35
Do you have access to an oscilloscope? That would make things very easy. – AsheeshR Mar 7 '14 at 9:43
I have had some success using an SG-2BC as a photoreflector, details of my build are here… – Bra1n Mar 7 '14 at 10:14
Most connections into meters are open-collector or volt-free i.e. a relay or NPN transistor. – Cybergibbons Mar 7 '14 at 10:24

Start with earthing the red (!?) wire to the ground of the arduino. Apply 5 volts via a 10k resistor to one of the black wires and also connect the black wire to the arduino as well. Basically :

5V ----(10K resistor)---+---Black wire----( Gas Meter)-----ground
                        +--- arduino digital input

You should either get a high or a low signal. Try the other black wire, it might be inverted (as in high and then pulse low, vs low and then pulse high).

Failing that, pop the top off that cover and have a poke around. Might give you a clue as to what's what.

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thanks @dgriffith, I'll give it a bash. so you think the two black wires are the same signal inverted? Why bother? – brettsonian Mar 10 '14 at 5:08

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