| Electronics > Projects, Designs, and Technical Stuff |
| Need some help building a circuit involving switchs and relays |
| << < (6/14) > >> |
| 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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