Using IR (InfraRed) radiation to control electronic devices is widely accepted and implemented. IR devices are routinely used in alarm systems, automatic door openers, and similar applications. This project makes use of coded IR emissions from a Sony TV remote, and a PICAXE microcontroller to manage the operation of a stepper motor. However, the same principles could be used for the control of AC or DC motors, relays, buzzers, lights, or almost any electrical or electro-mechanical device.
A trove of valuable information about infrared already exists here on AAC. Check it out by entering “infrared” or a similar term in the search box at the top of almost every page. Here are three examples:
- Create a Motion-Sensing Alarm with an Arduino and IR Sensors
- Signal Conditioning for Pyroelectric Passive Infrared Sensors
- Building an Infrared Tracker with a PICAXE 14M2 and a Stepper Motor
AAC also has additional knowledge available about the PICAXE microcontrollers. Here is a great place to start if you are not currently familiar with their operation and use, or you can use the AAC search engine to find more PICAXE references.
Not All IR Remotes Are Created Equal
Infrared remote controls come in a variety of sizes, shapes, and capabilities. Perhaps the simplest possible design is shown at the top of the photo below. It consists of an IR LED, a coin cell battery, a switch, and an enclosure to hold everything together (no series resistor is necessary because the battery’s internal resistance adequately limits the current through the LED). Operation of the switch connects the battery to the LED and produces IR light; that’s all there is to it.
The device at the bottom of the above photo is only a little more complex. The IR LED is housed in the black funnel at the top right of the enclosure; the funnel is intended to help direct the IR radiation toward the target. The printed circuit board just to the left of the funnel contains a push-button momentary switch. When the switch is operated, power is applied to an NE555 configured as an astable multivibrator. An RC (resistor capacitor) circuit controls the frequency of the multivibrator; in this case, the operation is at 40kHz, which is a common frequency for IR remote controls. The IR LED is turned on and off at that frequency for the duration of the time that the push button switch is held operated. Note that this 40kHz pulse is different from the frequency of the light being emitted from the LED, which, in this case, is at a wavelength of 940 nm (nanometers).
The purpose of the 40kHz oscillation is to reduce false triggering that might occur in IR receivers that simply sense the presence or absence of IR light. Better receivers are designed to react only to pulsing IR light and ignore continuous IR light. This reduces the likelihood of false triggering of the receiver by IR light from devices other than the intended transmitters. Not only must the IR light be pulsed, but the pulse frequency of the transmitter (40kHz in this case) must match the frequency to which the receiver is tuned.