| ??? 03/28/05 19:30 Read: times Msg Score: +1 +1 Good Answer/Helpful |
#90560 - AC-input optoisolator Responding to: ???'s previous message |
Geert Vancompernolle said:
In a domestic electricity installation, I want to switch whole circuits on or off by means of a, what we call, teleruptor relais. Don't know if this is the correct English word, but it's a kind of a relais, that has two steady powerless states (a relay has only one, since it falls back again, once the power is removed).
If you power the relais coil of the teleruptor, it switches to one position and it stays there until you power the relais coil again. Then it swiches back to the other position. In fact, a toggle relais which doesn't need power once a certain state is reached. It only needs power when the other state is to be reached again. But since you cannot exactly know in which state the teleruptor ended after powering the relais coil (the contacts can be closed, but they can also be opened), you need to 'spy' one way or another if the contacts are closed. One possibility is by means of help-contacts. These are potential-free contacts that are mechanically connected to the relais and those contacts "follow" the teleruptor. When the teleruptor is closed, so are the contacts of the help-relais. And vice versa. However, such help-contacts are quite expensive and I was wondering if you could 'sense' the output of the relais and bring this info (down-converted and separated by an opto-coupler, for instance) to the input of a detection circuit (0-5Vdc inputs), so that you exactly know the state of the relais in all possible situations. Does anyone know how such 'conversion' can be done? Maybe a ready-made scheme? Would be nice... Best rgds, --Geert I am not entirely sure what the device you are describing is. Is this some kind relay with two stable unpowered states, like a relay with latching capability? It seems though that the question you are asking has less to do with the nature of the switching device itself than it does with detecting the presence or absence of a large AC voltage. As you suggested, an optoisolator would be ideal here. Optoisolators are available in all shapes and sizes. Many have only a single LED on the input, thus allowing them to detect only one half of the AC waveform. Some feature two LEDs in parallel (hooked up with opposing polarity) so that they can detect both sides of the AC waveform. Although you could get by with either device if you choose to be clever, I suspect that you will find this somewhat troublesome, even if for no other reason than the lack of output during the zero crossing is likely to be a nuissance in your application. Although you could filter that out in hardware or software, you might be happier working with an integrated AC line monitor device like the Fairchild MID400. Use of this device is straightforward, and provides just about all the functionality required for detecting the general presence of an AC input on a macroscopic time scale; depending on your system, you will probably need little more than a current limiting input resistor. --Sasha Jevtic |
