This Photo Transistor Light Sensor is a simple sensor that detects ambient light. It’s kind of the opposite of an LED – when light hits the little chip inside, it induces current to flow from the long pin to the short pin. This sensor has a built-in optical filter (probably IR filter) so it’ll do a fair job of simulating light levels as the human eye does. Basically, connect the long + pin to 3-15VDC or so, and the short – pin through a ~1K-10K series resistor to ground. When its dark, there’s almost no current flowing through the sensor or resistor and the analog voltage is near ground. When there’s light near the sensor, the current through the resistor will increase, raising the voltage. You can adjust the series resistor to get the voltage range you need, and measure the analog voltage with a microcontroller.
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Stop breadboarding and soldering – start making immediately! Adafruit’s Circuit Playground is jam-packed with LEDs, sensors, buttons, alligator clip pads and more. Build projects with Circuit Playground in a few minutes with the drag-and-drop MakeCode programming site, learn computer science using the CS Discoveries class on code.org, jump into CircuitPython to learn Python and hardware together, TinyGO, or even use the Arduino IDE. Circuit Playground Express is the newest and best Circuit Playground board, with support for CircuitPython, MakeCode, and Arduino. It has a powerful processor, 10 NeoPixels, mini speaker, InfraRed receive and transmit, two buttons, a switch, 14 alligator clip pads, and lots of sensors: capacitive touch, IR proximity, temperature, light, motion and sound. A whole wide world of electronics and coding is waiting for you, and it fits in the palm of your hand.