interesting opto isolator circuit configurations

[SwitchSkillz]

Hi All

This is my first post here, sorry if its in the wrong section or a duplication.

I came across this youtube video and though it was very interesting, its on Julian Llets YT channel and he explains diiferent configurations of opto isolator circuits with some questionable results.

Take a look it does spark many questions and thought it may interest the forum.

https://youtu.be/tebprQvrqk4

Regards

Olly

[Ian.M]

Crappy circuit.   If you need to use a pair of optos in a push-pull configuration and want to avoid the leakage current issue, wire their LEDs antiparallel with a single series resistor to limit the input current.  You then get a choice of where to return the other side of the LEDs to - input side ground for simple positive/negative detection (provided abs(Vin)>Vf) or a rail maintained at 1/2 Vcc if you want logic levels like Julian  was using.    You can also get there by putting the input direct to one side of the LEDs and taking the other to a potential divider to both set the input threshold and limit the current, but you then have standing current in the divider.   Actively generating the 1/2 Vcc rail using a micropower OPAMP or other low quiescent current rail splitter avoids that, and its even easier if you can tap the 1/2Vcc point n a battery pack.