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Electronics => Beginners => Topic started by: slekvak on September 27, 2016, 07:11:59 am

Title: Is switching a hifi receiver push button using an optoisolator OK?
Post by: slekvak on September 27, 2016, 07:11:59 am
Hi!

My receiver has a speaker select (zones) toggle on the front of the chassis, with a simple push button behind it. As far as I can tell from the service manual, the button is switched to chassis ground and connected to a input on a microcontroller. I am planning on switching it with a Raspberry Pi or an Arduino.

Would it be safe to use a optoisolator for this, or do I need a relay? I have soldered two wires to the push button, shorting them seems to work fine, and was hoping I could use a "4N35 FSC Optocouplers Phototransistor 30V DIP6" I have available...

Snippets from service manual:
http://i.imgur.com/c55LtWU.png (http://i.imgur.com/c55LtWU.png)
http://i.imgur.com/AXZXay1.png (http://i.imgur.com/AXZXay1.png)

I hope someone is able to give me some advice (and/or comfort)  :)
Title: Re: Is switching a hifi receiver push button using an optoisolator OK?
Post by: Paul Moir on September 27, 2016, 07:20:16 am
Sure.  Richard Crowley turned me on to using optofets such as the H11F1M series because then you don't even need to know polarity.  But you have the parts and you have the schematic so that's no problem.

It's possible (but almost definitely not true) that they're putting some current through the switch which would mean you'd have to drive the LED pretty hard to "press the button".  You could simply measure the current going through the switch using a multimeter on a mA range.  The 4N35 has a guaranteed minimum current transfer ratio of 1, which means if you put 10mA through the LED it will allow 10mA through the phototransistor.
Title: Re: Is switching a hifi receiver push button using an optoisolator OK?
Post by: george.b on September 27, 2016, 04:17:58 pm
It should work. I mean, it's just a logic pin, I doubt it'll drain much current through the optocoupler.