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This small circuit activates a flashing LED when there is little or no ambient light, or night. When ambient light in the day or a lamp, the LED is turned off automatically by a photocell.

This flashing LED can be applied in several ways: In a bicycle as identification light, Christmas tree ornament in; caution night light in a backpack of a student, simulated alarm in a car or a house, etc.

Step 1: The Electronic Circuit.

The circuit is powered by two watch batteries: CR2032 and CR2016 another thinner in a battery holder button. Also contains a Silicon Controlled Rectifier or SCR C106B that triggers through the 33 Kilo ohms resistance when no light is incident to the photo resistive cell, then the SCR conducts electric current to the battery and flashing LED lights.

When ambient or artificial light inside the photocell, this decreases its value in ohms and removes power to the gate of the SCR, and the virtually grounded, and as the LED on and off by itself, the SCR turns off current zero at its anode. 
and the LED stays off.

This circuit does not work with LED fixed standard. It also has a power switch to turn it off when we keep our circuit.

Step 2: The Parts.

The required parts are:

1 Switch mini 1P1T
1 Button Battery CR2016  3V
1 Button Battery CR2032  3V
1 Flashng LED blue Ultra Bright
1 Resistance  33K
1 Photocell
1 SCR C106B
1 battery holder button

Step 3: Assembling the Components.

Here we show, step by step, like taking to support the battery button components welded.

Step 4: Operation.

This flashing light can be mounted easily on a bike helmet, for night ride. It works at night and turns off automatically during the day. Greetings and I hope will be useful.

About This Instructable

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