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Replacing phototransistor optocouplers in design

Question asked by Jack_Vaughan on Oct 31, 2013
Latest reply on Nov 13, 2013 by bkennedy



I'm currently trying to improve a stand-alone command device product that is designed to make/break the switches in separate devices that would otherwise be incompatible if they were all tied together at the ground of the command device. The controlled devices each have self contained/shielded embedded systems that manage analog audio circuits.  These controlled devices either have an existing input jack for a dedicated remote function switch or have been modified after-market for access to the logic pins/gnd of an on-board control switch. The command device is custom configured to be connected to two or two hundred different controlled devices. The software simulates each switch state required either momentary or latching and reduces the need the controlled device to run looped debounce routines if used (early forms used physical relays which were problematic). Typical connections are made via shielded cable.


I've used optocouplers in the command device (one for every connection) for several years now and have bumped into different issues in a few controlled devices:

- systems that will not respond to the transistors

- are more susceptible to (what seems like) a common mode transient from the coupler connection that winds up injected into the devices audio path

- with timing sensitive control there is excessive margin in the response time of any set of optocouplers, I need far more predictability for on/off times in order to better synchronize events in code.


What would be the most appropriate device/method/part to replace phototransistor optocouplers used to simulate switches in remote devices?


Key requirements:

- isolation

- will conduct 1 V - 5 V logic level signals

- the device to be controlled needs to see this as a physical switch which conducts equally well in both directions when on

- close on/off times

- SMD would be ideal


Any help or suggestions would be appreciated!