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i want to know code for counting the flashes of LEDs and display no. of flashes in particular time given.by using LDR. basically i tried it with interrupts but i'm not getting it,so please help in this regard.

  • If you post the code of your attempt, we might be able to help you. – uint128_t Mar 1 '16 at 15:39
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An hardware solution could be achieved by putting a photodiode or a photoresistance near the flashing LED. Connect it to a pin that supports external interrupt and you're done. With a bit more circuitry you can ensure that the value on the pin doesn't oscillate: put a Schmit Trigger after the photodiode or resitance with its output on the input pin.

  • The Arduino Uno already has Schmitt triggers on all its digital inputs. C.f. figure 14.2 on page 76 of the ATmega328P datasheet. – Edgar Bonet Mar 2 '16 at 9:31
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LDRs only give an analog output, proportional to the amount of light.

To make it give a HIGH and LOW value, you have to tweak the other resistor used in the voltage divider.

Alternatively you could use analogRead and add a threshold value in your code.

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