Electronics > Projects, Designs, and Technical Stuff
Need some help building a circuit involving switchs and relays
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Renate:
Well, could you take a photo of the original detector circuit board?
I'm sure we'd all be interested in how they did it.

The current transformer idea would work fine.
I just like my own idea.  ^-^
Shaydzmi:
Ok





Renate:
That's interesting.
First, the stacked power resistors are bypassed with a big solder blob.

I'm still confused.
Looking at those three bridge rectifiers/capacitor/top resistor/bottom resistor/optocouplers:
I can see that they are designed to detect a 24VAC signal.
Those half watt 3.3k (top) resistors make sense at 24 VAC = 7mA
Still, that 470 ohm on the bottom seems to steal too much of that 7 mA.
(I can't really tell because I don't know what the LED forward voltage is.)

It looks to me that there must be three external current transformers?
Something's going on here that I don't understand.
Shaydzmi:
You can look at only one section: Bridge, cap, 3.3k, 470, optocoupler

I think that 470 ohm is to reduce the voltage going to optocoupler.

The optocoupler gets 1volt, when the switch is closed.
Benta:
The stacked resistors are 330 ohms, not 3.3 k.

Current transformers may very well be external and mounted directly on the power leads, that would be the natural place.

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