IR detectors are little microchips with a photocell that are tuned to listen to infrared light. They are almost always used for remote control detection - every TV and DVD player has one of these in the front to listen for the IR signal from the clicker. Inside the remote control is a matching IR LED, which emits IR pulses to tell the TV to turn on, off or change channels. IR light is not visible to the human eye, which means it takes a little more work to test a setup.

There are a few difference between these and say a CdS Photocells:

• IR detectors are specially filtered for Infrared light, they are not good at detecting visible light. On the other hand, photocells are good at detecting yellow/green visible light, not good at IR light
• IR detectors have a demodulator inside that looks for modulated IR at 38 KHz. Just shining an IR LED wont be detected, it has to be PWM blinking at 38KHz. Photocells do not have any sort of demodulator and can detect any frequency (including DC) within the response speed of the photocell (which is about 1KHz)
• IR detectors are digital out - either they detect 38KHz IR signal and output low (0V) or they do not detect any and output high (5V). Photocells act like resistors, the resistance changes depending on how much light they are exposed to

In this tutorial we will show how to

• Test your IR sensor to make sure its working
• Read raw IR codes into a microcontroller
• Create a camera intervalometer
• Listen for 'commands' from a remote control on your microcontroller

Some Stats

These stats are for the IR detector in the Adafruit shop also known as PNA4602. Nearly all photocells will have slightly different specifications, although they all pretty much work the same. If there's a datasheet, you'll want to refer to it

• Size: square, 7mm by 8mm detector area
• Output: 0V (low) on detection of 38KHz carrier, 5V (high) otherwise
• Sensitivity range: 800nm to 1100nm with peak response at 940nm. Frequency range is 35KHz to 41KHz with peak detection at 38KHz
• Power supply: 3-5V DC 3mA
• PNA4602 Datasheet (now discontinued) or GP1UX311QS or TSOP38238 (pin-compatible replacements)

What You Can Measure

As you can see from these datasheet graphs, the peak frequency detection is at 38 KHz and the peak LED color is 940 nm. You can use from about 35 KHz to 41 KHz but the sensitivity will drop off so that it wont detect as well from afar. Likewise, you can use 850 to 1100 nm LEDs but they wont work as well as 900 to 1000nm so make sure to get matching LEDs! Check the datasheet for your IR LED to verify the wavelength.

Try to get a 940nm - remember that 940nm is not visible light (its Infra Red)!