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I am trying to replace a analog switch (the switch is a momentary button in a low current DC situation) with optocoupler.

Is it possible to use an optocoupler as a switch (i.e. just on/off)?

Ignoring the current/voltage that optocoupler is capable to output.

EDIT:

Is it possible to use an optocoupler to short two wires carrying low current DC signal?

Basically I am trying to hack a circuit and add Arduino control to it and from my testing I am unable to obtain much more info.

Hope this makes it clear...

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    \$\begingroup\$ yes, because an optocoupler is just a transistor with a light-sensitive gate/base. \$\endgroup\$ Mar 1, 2019 at 12:25
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    \$\begingroup\$ As you can probably tell from the answers you're getting, you haven't provided enough information about your use scenario to get anything definitive. Can you provide detail about the signal you will be switching, and the signal you will be switching it with? Voltage range and current demands would be a good start. \$\endgroup\$ Mar 1, 2019 at 13:23
  • \$\begingroup\$ Added low current DC signal is being attempted to switch. \$\endgroup\$ Mar 1, 2019 at 13:34
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    \$\begingroup\$ Still not really enough for the output side. Does your load need to be attached to ground on the low side? What is the low current DC signal for? Is it just going into a high impedance amp?? No kidding -- the more info you provide, the happier you'll be with your answer. Don't make us beg for the info. \$\endgroup\$ Mar 1, 2019 at 13:37
  • \$\begingroup\$ @ScottSeidman, Sorry for that, Basically I am trying to hack a circuit and add Arduino control to it and from my testing I am unable to obtain much info. Right now can you just tell me if an optocoupler can short its terminals even when they are not connected to anything like when a switch is on. \$\endgroup\$ Mar 1, 2019 at 13:46

4 Answers 4

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The optocoupler you specify is not a "short" between it's output terminals. If you don't have a perfect understanding of the device you'd be driving, a relay is probably a safer choice.

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You may be able to. An optoisolator (or SSR) with a MOSFET output (actually two series MOSFETS to handle AC) acts more or less like a mechanical switch.

Imperfections include some ‘on’ resistance, relatively slow and asymmetrical turn on and turn off times, and large capacitance (limiting the ‘off’ impedance at high frequencies). The on resistance changes with current somewhat, causing some distortion, which may or may not be significant in your application.

A mechanical relay is a much less imperfect switch, however it suffers from different limitations.

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The output of a "normal" optocoupler is an NPN transistor. It is very good at switching a low current DC voltage. It is not very good at switching an AC signal such as audio.

There are optocouplers with MOSFET and TRIAC outputs that are better for AC signals, but they have their own quirks. Without knowing more about the signal you want to switch, and explaining what "bidirectional stuff" is, how do you expect any kind of clear answer?

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Look for a solid state relay. It's bidirectional like a (mechanical) relay, whereas an optocoupler isn't.

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  • \$\begingroup\$ On many forums, people were recommending a solid state relay. Can you provide some more details, i.e. I just want either on/off (no bidirectional stuff). \$\endgroup\$ Mar 1, 2019 at 12:58
  • \$\begingroup\$ I wouldn't know what more details. Could you please provide some more details what you want? Try making "I just want either on/off" more clear. (Please use the edit function to provide more details to your original question) \$\endgroup\$
    – Huisman
    Mar 1, 2019 at 13:04
  • \$\begingroup\$ Some more details on suitability of optocoupler in only uni direction application (i.e. either on/off like an analog switch). Basically I want to replace a momentary button in an external circuit. \$\endgroup\$ Mar 1, 2019 at 13:14
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    \$\begingroup\$ Optocouplers use their light junction to drive a BJT output, whereas an ssr drives a push-pull configuration of mosfets. To tell which one is better suited to your application we would need to know a bit more about the rest of your circuit, like how it is turned on. \$\endgroup\$
    – Stiddily
    Mar 1, 2019 at 13:18

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