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How to illuminate a wall-clock with leds and a light sensor ? Answered

I want to illuminate a wall-clock using a light sensor and leds from a 1.5\3.0\9.0 volt batteries.What components i need for a long lasting but simple circuit ?


what is the light sensor for? You want to turn on the LED's when it gets dark??

hello smokedasphalt, That is correct.I want the face to be illuminated during the dark hours,and leds to go off during the day.

Use an LDR. Check out Seandogue's answer, i was gonna tell you to do the same thing. But, instead of an op-amp, rather use a comparator. Like the LM339. It is a very common IC.

One method is to use a CD cell for light sensing. Basically a light dependent resistor, also known as an LDR. They last for years. You can use it in a voltage divider that drives one of the inputs to an opamp with moderately high gain, the other input is set using a fixed reference. When the voltage exceeds the value, it flips the state of the output from high to low or low to high. This output is either used to drive a Fet, BJT or relay which in turn powers the LEDS. To adjust the circuit performance, one uses a trimmer on the fixed reference so that the circuit operates according to expectations wrt "light" and "dark" or conversely uses a trimmer on the voltage divider in the same basic manner. There are other methods for achieving the result. This is just one.

Or this one. You'll have to modify it to drive more leds though.