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It should work and control an INCANDESCENT light so it gets brighter as less light falls on the LDR. Do not try to use it with low energy lamps as most are not dimmable. Beware that the whole circuit is 'live' so all parts of it must be insulated from being touched. Also try to keep the LDR away from light emitted by the lamp.
It should work and control an INCANDESCENT light so it gets brighter as less light falls on the LDR. Do not try to use it with low energy lamps as most are not dimmable. Beware that the whole circuit is 'live' so all parts of it must be insulated from being touched. Also try to keep the LDR away from light emitted by the lamp.
The circuit is designed for dimming. It is using phase control by a triac to reduce the effective voltage to a regular lamp. Both LED and CFL lamps have built in drivers that are resistant to voltage change. So CFL and LED lamps will not work in this circuit.
You can make a new design to turn lamps on and off using a set threshold of ambient light. Such a circuit will work with CFL and LED lamps.
Better search for a on-off circuit for light control (similar to ones used for control of street lights).
The circuit is designed for dimming. It is using phase control by a triac to reduce the effective voltage to a regular lamp. Both LED and CFL lamps have built in drivers that are resistant to voltage change. So CFL and LED lamps will not work in this circuit.
You can make a new design to turn lamps on and off using a set threshold of ambient light. Such a circuit will work with CFL and LED lamps.
Better search for a on-off circuit for light control (similar to ones used for control of street lights).
I found the following circuit , could you advice to use it ?
I tested the circuit using simulator .
With pnp transistor not working,
When i used npn transistor bc548 it works when i increase the coil resistance of the relay from 240ohm to 480 ohm.
The transistors should be NPN. The circuit should work but it still has soft operating point. The relay current is depedent on the light level, obviously the contacts will make or break suddenly but if the coil current is marginal there is a risk of them arcing. Note that the input capacitor MUST be rated for full AC line voltage and I would advise you add a fuse in series with it. If the value is wrong or the capacitor fails it will cause catastrophic failure of the other components.
The relay current is depedent on the light level, obviously the contacts will make or break suddenly but if the coil current is marginal there is a risk of them arcing...
Unless there is some significant hysteresis, this is not going to be useful. Even with a big capacitor at the base of the switch, it is not going to be useful because the relay drop in and drop out voltages are not the best way to introduce the hysteresis.
The transistors should be NPN. The circuit should work but it still has soft operating point. The relay current is depedent on the light level, obviously the contacts will make or break suddenly but if the coil current is marginal there is a risk of them arcing. Note that the input capacitor MUST be rated for full AC line voltage and I would advise you add a fuse in series with it. If the value is wrong or the capacitor fails it will cause catastrophic failure of the other components.
Better, but it has some problems. It works from a DC 12V supply so it won't directly operate your lamp. You could change LED1 for a relay coil and remove the series resistor, you could then use the relay contactsto switch the light. If you do that you should also connect a diode across the relay coil with cathode end to the supply. There is a major problem though, when you use an op-amp as a comparator you are comparing the voltage at LDR/R2 with the voltage at the wiper of R1 but that in turn depends on the supply voltage. Because you are using a capacitor to drop AC line voltage to DC supply, the voltage will vary according to the current the circuit takes. That means that as the relay turns on, the extra current it draws will drop the supply voltage and therefore the voltage from R1. You could well end up with a flasher circuit!
The easiest fix for that is to connect a 12V Zener diode across the supply to stabilize it. It should pass the same current as the relay coil. You can then work out the capacitor value to give 12V at that current. It becomes a shunt stabilizer,inefficient but simple. The fuse rating should be as low as possible but more than the relay coil current plus about 50%.
The bigger worry is that you have kept the turn-on and turn-off at the same value. This is not desirable.There should be some dead band between the turn-on and turn-off levels.
Why not use the suggestion made in #8?
Borrow the ideas but not the circuits. Running from 12V batteries is good but if your lamp runs on 220VAC, then it will be messy because you will need two sources of power...
i test the following circuit on breadboard and i see it works fine.
the relay activated on a certain light intensity and off on another one.
when i change R2 to 1M i see the gap between relay on and off increased.
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