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a potential divider will do,
i have included a picture, variable resistor 1 is to set the threshold at which the circuit turns on, if a heavier load is to be drive replace LED1 with a relay and reverse bias a diode across the relays terminals to prevent electromotive feedback.
it helps but i need tha practical circuit schematic , is that enough to use only one transistor and three resistors for accuracy working? and if the load requires high current draw and voltage about 220v as neon lamp.. i know that relay can lead high power elements but the supply here in only 9v, how would it be?
you could power thecircuit via a transformer, or i suppose it could be powered from the mains if rectified as long as componets with suitable values were chosen, the variable resistor might pose a problem, if the variable resistor had a metal base it would have to be earthed and the circuit placed in a plastic box(or earthed metal one). The light would not either be on or off, it will illuminate proportionally to the darkness.
the circuit below will be definite on or off as it uses a relay, this is one way of doing what you require another is without the transformer(the bottom schematic) personally i would use the one with the transformer.
Please don't post diagrams (or anything else) as BMP files, they are stupidly huge, use either GIF or PNG instead, exactly the same quality and probably only 1/100th the size!. Don't use JPG though, although it's a LOT better than BMP, it's still much bigger than GIF or PNG.
i've made the circuit on PCB and tried to check it, my two-connector relay swirched on at first but then no resonse from it with the same experiment conditions...that's when relay is not loaded ( I havent yet load it)
is there any relation between switching and relay loading?
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