AC device interfacing

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RishabhG

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Hi

I want to detect whether an electric bulb is on/off using a microcontroller. How can it be done? I know we can turn it on/off using relays but how to determine whether it is already on/off when it is also connected through the mains supply connection.

Thank You
 

hello,

The better way could be to use a LDR (Light dpendant Resistor) connected on Analog input
ex: LDR of 1meghom in the dark less than 1K face on the Buble light
do a divider with +5V --- LDR -|--10K --- OV
and middle LDR & 10K connected to ADC input..
Measure ADC value and compare to a numerique value as threshold to put a Flag ON or OFF
Light is ON or OFF

I use it to check my Gas Furnace (Central Heating) On or OFF
LDR face to a little buble light.
 

Greetings,
Best and cheap way has already been said by paulfjujo. Use a Photoresistor (ie. LDR), its whole circuit is very easy to make and that will be cheap too.
Other solutions may be -
- Photovoltaic cells or solar cells.
- Photodiodes.
- Phototransistors.
- Photomultiplier tubes and more..

Moreover you can use temperature sensor if the light bulb gets warm or if it is tungsten filament lamp as it gets hot while on.

Good Luck
 

The idea of LDR would be useful only during the night time I believe;what about day-time?
Actually I also want to use the same technique for other AC devices as well. The LDR would only be useful for light bulbs. Sorry did not mention this before.

The AC mains supply ratings are 230V,50Hz.

@jayanth.devarayanadurga How can we sense the current in the bulb circuit?
 

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