Introduction: Simple Dark Detect LED Robot's Flashlight

About: I work in industrial automation and spend any free time making.

I'm going to show you a simple, adjustable light sensor circuit that activates in low light.
Light sensing circuits are versatile and simple enough for beginners to build but have many useful applications.
The circuit I am presenting is to be used as a headlamp for my robot A3-8D (anyone in manufacturing may get joke.) This lamp will automatically turn on when the robot enters a dark room. This will save precious microprocessor inputs and outputs.

Step 1: The Schematic and the Parts

The schematic is daily simple and there are not too many part required
Parts you will need:
- LEDs from a dollar store flashlight
- 1 x Transistor 2N4401
- 1 x Photoresistor
- 1 x 100 ohm resistor
- 1 x 100K ohm Variable-resistor
- Breadboard and hookup wire
- Perfboard, wire and soldering materials

Step 2: Prototype Before Soldering

Even a simple circuit like this I take the time to layout on a board board and test before soldering. It's better to find you have a bad component or bad idea here than once it is on the CB. Desoldering is a pain.
I soldered some solid core leads on my led package to make it easier to breadboard.

Step 3: Solder It Up and Cable It

I laid out my board so that the POT is facing out the direction of the lamp. When this is placed behind the skin of my robot I can have an access hole for adjusting the ON sensitivity without removing any panels.
Run 2 wires to the board for power and ground. I will be powering this with 5vdc.

Step 4: Mounted and Tested

This the Lamp mounted in the robot skin of A3-8D. The lamp works great too bad the robot is not autonomous yet.
He is pretty bare bones so far with only a USB power charging port and Bluetooth speaker system and a few sound sensors. I will share this circuit as soon as I can get it wrote up.

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