Adafruit
Photo Transistor Light Sensor
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 litt...
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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 pin connected to the 'thicker' part of the sensor to 3-15VDC or so, and the thinner-part 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. If you're not getting any readings, try flipping the sensor around.
These are, essentially, replacements for CdS photocells, but are RoHS compliant.
Jargon buster
Plain-language definitions for the technical terms used above.
- LED
- A light-emitting diode (LED) is a small electronic component that emits light when current flows through it in the correct direction. Because it only conducts one way, its polarity matters, and a through-hole LED must be soldered the correct way around to light up.
- microcontroller
- A microcontroller is a small computer on a single chip that runs a stored program and controls connected inputs and outputs such as buttons, sensors, displays and communication interfaces. In a device built around one, it is the part that executes the code and coordinates the device's behaviour.
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