Tips & Tricks: IR LED

It’s invisible to the eye!

IR_LED_1LR

IR_led2

The IR LED (or infrared light-emitting diode) module sends out light with longer wavelengths than visible light, similar to the light in your remote control. It’s invisible to the eye, but many digital cameras can see it! Try using it to activate the light sensor or remote trigger.

The Remote Trigger is a light sensitive trigger module that sends a brief ON signal when it senses infrared light. This makes it a perfect bit to pair with your IR LED if you want to send simple ON and OFF signals through a circuit. Below are two different ways you can use the IR LED with the Remote Trigger. One will just send a brief ON signal, while the other will keep sending the ON signal for as long as the IR LED is shining on the Remote Trigger.

Using the IR LED with the Remote Trigger

In the video below we have two simple circuits. The first one powers our IR LED whenever we press a button: Power → Button → IR LED. The second circuit uses the Remote Trigger to turn on an LED whenever it detects infrared light: Power → Remote Trigger → LED. When we press the button on our remote, the IR LED sends out infrared light. When the Remote trigger senses the infrared light, it lights up the LED, but only for a moment. Even when we keep our finger on the remote button, the light turns off. To light up the LED again, we need to let go of the button and then push it again. This is because when the Remote Trigger senses infrared light, it sends a quick ON signal through the circuit, but it doesn’t stay ON like the other Trigger Modules.

If you want the Remote Trigger to keep sending the ON signal, you need to keep turning your infrared light source ON and OFF. If you switch between ON and OFF fast enough, the bursts of ON signals will overlap, keeping the circuit ON all the time. To do this, you can add a Pulse Module to your IR LED like this: Power → Button → Pulse → IR LED. When building this circuit make sure you set the pulse to the highest speed. In the video below you’ll notice that when we press our remote button this time, the LED stays lit up, and when we let go of the button, the LED turns of.

 

Using The IR LED with the Light Sensor and an infrared filter

The Light Sensor also responds to infrared light, and unlike the Remote Trigger it sends more than an ON signal. The Light Sensor works more like a dimmer—the brighter the light, the stronger the signal it sends through the circuit (or the darker the light if you’re using it in dark mode). The Light Sensor can read both visible and infrared light, so the IR LED will work best with the Light Sensor if you can find some way to block out visible light that also triggers the sensor. You can either use your sensor in the dark or you can use an infrared filter. Infrared filters only let infrared light through, so by placing it over the Light Sensor, you’ll only let infrared light pass through to activate the sensor.

In the video below, we are using the IR LED to beam a music signal to a Light Sensor attached to a Speaker. At first the signal is very weak because the visible light is drowning out the infrared signal. When we turn on a nearby lamp, the infrared signal becomes totally drowned out and the music stops. However, when we put an infrared filter over the Light Sensor, the music comes back louder than ever.

 

Our Satellite Data Communication project used an infrared filter. An IR LED on the satellite beamed information down to the satellite dish. A filter on the dish covered the light sensor and ensured that data from the satellite came in loud and clear.

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You can use an infrared filter from a camera lens, but if have some old floppy discs lying around, the thin magnetic film from the disk works pretty well. We built the filter we used in the video above from one of these disks and a small cardboard tube.

 IR Filter from Disk 2

DIY IR Filter

Night Vision! Using the IR LED with a digital camera:

 Some cameras respond to infrared light, which means that with the IR LED you can take some cool night vision photographs. The first thing you will want to do is test to see if your camera can “see” infrared light. Connect your IR LED to a Power module and head into a dark room (the darker the better). Hold the LED close to and directly pointing at the camera, then take a picture. Most cameras see infrared as purple light, so if you see a very faint purple dot you know your camera can take pictures with the IR LED. Now it’s time to start taking your night vision photos. Because the infrared light is very faint, long exposures work best. Below are some night vision shots we took in a closet in our office.

We tried a couple of different setups and found that you could take great shots with only one IR LED but you would need a tripod to hold the camera steady for the long exposure. We also put together an array of eight IR LEDs so we could shorten the exposure time:

 Night Vision Setup

Once we had everything set up, we turned of the lights. This is what our eyes saw:

Night Vision Total Black

But this is what our camera saw:

Reindeer

 This was taken using one IR LED with a 30 second exposure time.

Using the IR LED with the Motion Trigger

 Our Motion Trigger module works by detecting slight changes in infrared light. Anything that moves within the vision of the module will change the light hitting the sensor and trigger it. If you want to trigger the sensor without using movement, you can also use the IR LED. In the example below we placed the Motion Trigger in the bottom of a cardboard tube and the IR LED in the top of the tube. Whenever we press the button, the IR LED turns on and triggers the Motion Trigger. We put the modules inside the tube because the Motion Trigger is very sensitive and just the movement of pressing the button would set it off. If you want to try this experiment without the tube, you could try using a wireless module.

 

Explore More:

Curious about what infrared light is? Check out NASA’s Mission Science to learn more: (http://missionscience.nasa.gov/ems/07_infraredwaves.html)

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