optoisolators

[Foaad]

Does it matter where you put the resistor at the hot side or common?
I'v seen designs that did them either way.
Im actually using the transformed voltage 8VAC instead of the 120VAC
I hope this didnt introduce any phase delays
Its working since im getting a 120Hz square wave with 4.88V pk-pk
How do i improve the shape of the wave, its more like triangular
and what should i be considering before connecting the wav to the MCU's port pin.

Thanks again

 

[James Beck]

Does it matter where you put the resistor at the hot side or common?
I'v seen designs that did them either way.
Im actually using the transformed voltage 8VAC instead of the 120VAC
I hope this didnt introduce any phase delays
Its working since im getting a 120Hz square wave with 4.88V pk-pk
How do i improve the shape of the wave, its more like triangular
and what should i be considering before connecting the wav to the MCU's port pin.

Thanks again

The location of the resistor does not matter.
I would still use something like a 1N914 as a blocking diode, most optos
have a PIV rating in the 3V range. It will clean up the wave form some,
since the opto diode won't have such a large recovery time when it isn't
being over stressed. You might even try placing the diode in a reverse
direction of the opto diode. That way the opto led never sees more than
..7V or so reverse. Although this configuration will increase the power
that the resistor has to dissipate. Change the 10K resistor to a 560
ohm 1/2 W or so and see if that perks things up too, since you said you
are running at 8VAC not 120VAC.

Jim