Introduction: 555 Timer, Variable Blinking Light

Picture of 555 Timer, Variable Blinking Light

Thank's to the Instructables Build Night sponsored by, hosted at, I bring you a 555 timer based project that blinks an LED at a rate that's affected by the intensity of the light in the room!

Things you need:
- breadboard
- 9V battery
- couple of resistors
- Photo-resistor, or LDR
- many jumper wires

Step 1: Connect All the Things!

Picture of Connect All the Things!

Wire up the circuit on a breadboard.  There's some leeway in the resistor values.  Changing the 10K will change the blink speed, and the 3.3K you should change based on the LED you use.

Step 2: Move Around to Different Lighted Areas!

Picture of Move Around to Different Lighted Areas!

It should blink faster with more light!

Thins to do:
- add an inverter circuit so that it'll blink faster in darkness!
- try different LED's!  the big yellow one was in Jameco's grab bag, it has 6 LED's inside it, all 5V forward voltage which is why I took the resistor off.
- replace the LED with a buzzer!  place in your refrigerator to see if the light stays on when the door is closed!
- replace LED with a transistor and drive a big high power led!
- replace photo-resistor with a trim pot and set your own blink rate!


makeosaurus (author)2015-04-08

what is the value of the capacitor

chrwei (author)makeosaurus2015-04-08

it's on the schematic, 10uf. for this project voltage isn't very important, but it should be an electrolytic type.

syedhamzahasan (author)2014-05-13

You can increase or decrease sensitivity of LDR's Light sensing ability by adding a Variable Resistor/Potentiometer with LDR.
Nice instructable though

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