How to Build an Infrared (IR) Detector Circuit

In this project, we show how to build a simple infrared (IR) detector circuit.

This is a circuit which can detect infrared light.

To build an infrared detector circuit, we will need the following electronic components:

Components Needed

• IR Phototransistor
• 330Ω Resistor
• LED
• 9-volt Battery

Here you can find a wide variety of IR phototransistors at Jameco.

The circuit we will build from these parts is:

IR Detector Circuit

This circuit is very simple.

When the IR phototransistor isn't exposed to any infrared light, there can be no current flow through the transistor, because infrared light is what produces base current in the transistor. The base current triggers a larger current from emitter to collector. Without infrared, there is no base current. Therefore, no amplified current can be produced.

When the transistor is exposed to infrared light, a base current is produced. This base current triggers a larger current from emitter to collector. If you expose the IR phototransistor to an infrared light source such as an infrared LED, a TV remote control, a flame, or sunlight, the LED will light up. This is because the infrared induces a base current in the transistor, which causes sufficient current amplification to drive and light the LED. Without the infrared light, no base current will be produced and, thus, no amplification will occur. The infrared light is what triggers the whole transistor to allow current flow.

And this is how the IR detector circuit works.

Testing the Circuit

Again, when testing this circuit, the sunlight will make this circuit work, since the sun emits infrared light, as do flames as well. Probably the best way to produce the infrared light, though, which you will need to test this circuit is an infrared LED.

An infrared LED is an LED which emits infrared light. We cannot see infrared light, because it's outside of the visible spectrum, which is why we build circuits to be able to detect it. Infrared LEDs can be found at many online retailers. The LED is usually a dark purple or blue color. Like other LEDS, the cathode lead is shorter than the anode LED, so it connects the same way in a circuit as you would a regular LED.

To produce infrared LED from an IR LED, you just give the LED sufficient voltage and it will emit infrared light.

Just place the DC power which the LED needs for power. Check the datasheet of the IR LED in use to find out how much voltage it needs. It will be called the forward voltage on the datasheet. Also check the maximum forward current listed on the datasheet and use a resistor to make sure the LED does not receive more than this specification. Once the LED is supplied with the sufficient current, it will emit infrared light. With it emitting IR light, now just point the IR LED to our original Infrared (IR) detector circuit. This will trigger the LED to light in the circuit. And, thus, our test will be complete.

To see the project where we have built an IR LED circuit, see the IR LED Circuit project here.

Related Resources

How to Build a Proximity Detector Circuit

How to Build a Dark-activated Light Circuit