OK,
thank you very much for your availability. I'm asking to myself if it's strange what I'm trying to do. What do you think ? How would you use PWM and optoisolator ? Do you have any _link_s where I can learn more ?


Thank you,
Pasquale.

Ciao,

Unfortunately this is the correct use of optoisolator, a safer approach. The use of transistors is quite regular in this applications. You have to consider that voltage isolation is a critical issue.

You can still use the optocoupler led drive circuit that I sent to you (the last picture that I uploaded). You can change the optocoupler output stage connection. See the image attached. In this case we have a pull-up connection. When the pwm is high the optocoupler transistor is on and the V_out will be +5V. In your connection if the optocoupler transistor is on will pull-down the V_out.

If you search in internet you can find lots of info (i.e. http://www1.jaycar.com.au/images_uploaded/optocoup.pdf )

Francesco.

Sorry,

just a remark on your schematic and my last message.

Try to remove the R2 in your schematic and _link_ the pin 6 (optocoupler) directly to +5V. _link_ pin 5 to a resistance that goes to gnd (you can simply move R2 from the collector to the emitter). Than the V_out (pwm output) will be pin 5. Make some trials to find the optimal emitter resistance.

Francesco.