# 200mv pulse to 12v lock

#### raulthree

##### New Member
I have a circuit that
produces 2 pulses of (200mv)-(2v) when transitioning to On state
and
produces 2 pulses of (-200mv)-(-2v) when transitioning to Off state

I have would like to use these pulses in the simplest way possible to control a switch/relay/circuit
+12v on state
0 volt off state

the 12v would be powered by a source separate from the existing circuits power source.

##### Active Member
Whats the drive current available from the pulse generators ?

Regards, Dana.

#### raulthree

##### New Member
looks like 80-100 mA

#### raulthree

##### New Member
So I'm doing some homework on optocouplers now the lowest input voltage I've found is 3v but I feel like this might be the right track. It's just so difficult to find something for those low power inputs.

#### Nigel Goodwin

##### Super Moderator
So I'm doing some homework on optocouplers now the lowest input voltage I've found is 3v but I feel like this might be the right track. It's just so difficult to find something for those low power inputs.
I suggest you are more specific, and tell us EXACTLY what the source is - as the wide range you suggest means you need an opamp to amplify it before you can do anything useful. 2V would be no problem, as you could switch a bipolar transistor easily with that - but then there's the confusing positive and negative thing.

#### raulthree

##### New Member
I'm getting those numbers with a multimeter. I've measured the voltage as the system goes off and on about 40 times . The non transition voltage is 0. The numbers stated earlier encompass all of the readings.

#### Nigel Goodwin

##### Super Moderator
I'm getting those numbers with a multimeter. I've measured the voltage as the system goes off and on about 40 times . The non transition voltage is 0. The numbers stated earlier encompass all of the readings.
You've still told us nothing?. And if you're measuring pulses/AC with a multimeter then it's completely meaningless anyway.

##### Active Member
Does your multimeter have a AC peak reading function ? If so check its specs
in manual if you can capture 200 mS or less peaks.

If you have a f() generator set it up for 400 ms, 2.5 Hz, 2V and see what your meter reads.

An oscilloscope would be real handy for this measurement.

Use a bench power supply, set your meter to resistance, and connect it to NO contacts on
relay and see what V it energizes at.

These can all give you clues.

Your pulses are 2.2V, most opto couplers input LED turn on between 1 - 2 V, so thats not
an issue. Just limit the input current to datasheet spec allowed. Use a R to do this. Its output
current capability to feed the relay coil you need. And off state voltage on the transistor it
can tolerate.

Something like this -

Just go to digikey and use filters to get needed relay current thru output of coupler
and say 2X the 12V in system for output transistor breakdown margin. Transistor output.
100 mA for coil current, although there are many relays << 100 mA to turn on......

Regards, Dana.

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