Optoisolator choosing correct one

[Coopznz]

Hi guys and girls

I have a Hydrawise Irrigation controller which takes an input for a flow meter, its based on a simple switch device ie reed switch but the Hydrawise flow meter is between $400 and $500 so no thanks far over priced, I have found a really good 50 mm flow meter for around $80 which is now plumbed in and ready to go, issue is the new flow meter is hall effect (3 wire) and the Hydrawise controller supplies its own 5 v output for the flow meter (two wire) , simple solution to me is to use an Optoisolator sitting between the units and I successfully set one up on the bench with a scope and was able to operate it with a 12 v supply on the input side and a 5 v supply on the output, before I commit to this method I discovered there is multiple types of OptoIsolators and are now a little confused on which one will be best?

 

[The March Muppet]

I'm not dense, but I may be missing something; as I read - the old controller system is looking for a simple switch closure, the new meter requires 5V, GND, and outputs a hall signal? So I assume you have the supply rails reckoned, and are just trying to close a 12V circuit with the hall output?

If you have a working bench setup, why do you think that the isolator you're using isn't sufficient?

Aye, there is indeed a variety - all the way up to killowatt "Solid state relay" triac drivers - how much current are you switching?

As well, whatever works works - but you very well may be able to perform the same function with a transistor.

 

[Coopznz]

I only had a chance to do a quick bench setup while home, I am now back at work, New meter requires 12v GND and outputs a half signal, you cant input the hall effect device direct to the Hydrawise controller, in fact the input at the Hydrawise controller I was unable to determine what voltage they are using (you have no true ground to test too)

 

[KeepItSimpleStupid]

I can;t figure out what your trying to say either.

Generally, you have a sensor and a meter or you can have something like https://proteusind.com/wp-content/uploads/2016/06/8000TRM.pdf
and a readout.

You can see some sensor wiring here: https://assets.omega.com/manuals/te...flow/paddlewheel-flow-meters/M3814.pdf#page-4

A sensor might just be +5, gnd and an open collector output transistor.

If you requre an open collector sensor and the sensor is not, you can add a Shockley diodse or sometimes a regular diode.

Look at the output of your sensor, unpowered with the diode function of your DVM. Also check for resistance to the + power supply.

Check the readout too, to see if the input is pulled up to some level.

You can load the readout with a potentiometer until he voltage is 1/2. Measure the pot and this is the input Z of the readout.

OPTOMOS relays, basically an optocoupler have really low input current requirements, on the order of 1 mA, but you;ll have to add a resistor.

There are lots of optocouplers, but the OPTOMOS relay, the schmidt trigger, FET and bi-polar transistor might be worthwhile to look at.

A diode might be all that's required.