Thanks, that's what I'm looking for. On the DC side, can I use a=20
capacitor to ground to eliminate the software filter? This will be very=20
low speed circuit where the period might be measured in many minutes.

:) :)

On 9/16/13 9:34 AM, Isaac Marino Bavaresco wrote:
> The opto-isolator is a good idea and is what I use.
>
> If the speed of detection is not critical and you don't need to know the
> phase or zero-crossing instant then a simple LED+Transistor opto can be
> used.
>
> If the opto is not designed for AC it has as single LED and you will
> need to connect a diode in parallel with the LED, in the opposite directi=
on.
> In series with the opto (or opto//diode) use a capacitor in series with
> a low-value resistor (120 Ohm is good) just to limit the inrush current
> in the capacitor.
>
> The capacitor can be calculated easily: Xc =3D 1/(w*C).      w =3D Omega =
=3D
> 2*Pi*F
>
> So, if you have 120V 60Hz (USA, right?) and want an average current of
> 15mA then Xc is approx. 8000 Ohm
>
> C =3D 1/(w*Xc)
>
> C =3D 1/(2*Pi*60*8000) =3D 331nF
>
> Use a Mylar capacitor with working voltage of 250V for 120V line voltage
> and 400V for 240V line voltage.
> Note: Do not use metal-film resistor, just a plain old carbon film one.
> The wattage can be 1/8W.
>
> When on, the output will be pulsating. You can filter it with a physical
> low pass filter or do it in software.
>
>
> Best regards,
>
> Isaac
>
>
>
> Em 16/09/2013 09:33, Carl Denk escreveu:
>> I have a home project coming down the road mainly HVAC stuff of digital
>> inputs to a PIC probably a 18F??. THe inputs would be only to sense
>> on/off. The voltages would be 24 VAC, 120 VAC, and 240 VAC. I'm thinking
>> through an Opto isolator with a resistor and capacitor on the AC side.
>> Values ? Configuration? or something else?
>>
>> This is a low priority at the moment, but thought I would generate some
>> traffic for Bob. :)
>>
>> Thanks again.

--=20
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