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led dimmer circuit by using photocell...help me

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tmmizwan

New Member
I have a circuit which can make led dimming by using 555 ic. In this circuit potentiometer is used to control the dimming. But I want to make led bulb dim depend on ambient brightness. So how can I connect the photo sensor like LDR to this circuit in order to make the led dim based on surrounding brightness.. Here I attached my circuit. anyone who know about it, please help me......
 

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amitak

New Member
simply replace the pot with an LDR .. you shall have to recalculate the values of the resister - capacitor network ..
 

be80be

Well-Known Member
You could do it like this real easy just try to match your ldr's
 

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tmmizwan

New Member
thanks to amitak and be08e.

i have tried this circuit by using ldr. the problem is the led on with high brightness even in presence of high brightness of ambient light. when in the dark the led is blinking. I want the led off in the presence of enough ambient light. and will bright gradually when the ambient brightness is gradually become dark..

the second question is.. can i replace the led with small bulb.
 

amitak

New Member
to invert the led golw style skip the npn transistor and connect led's from vcc to the output of 555 (calculate the sink current that the 555 should take and verify that it is within limits)
to use the bulb too you need to calculate the current needed by the bulb, a bulb working on dc can be directly connected if the current needed is wothin limits
for an ac bulb or a bulb with higher current i suggest an opto coupler
the input bias of the opto coupler can be sink or source to get the on/off condition of led required
 
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