Build Your Own IR Detector Circuit – 950nm Sensing

Circuit diagram:

Circuit description:

Men frequently find value in the usability of television remote controls – often to the frustration of their female companions. Gentlemen appear to desire to know precisely what they are overlooking while the television is tuned to a specific broadcast, so they tend to continuously shift channels. Equipped with the control device in their possession, they perceive themselves as the supreme authority over the television set. Consequently, they are entirely bewildered if the control device malfunctions. Several reasons can account for a remote control unit failing, such as a defective infrared receiver within the television, a defect in the remote, or depleted batteries. Here a testing instrument capable of ascertaining whether the remote control unit still transmits an infrared signal proves invaluable. To maintain firm control of the infrared signal, one can construct their own infrared detector.

If you possess a number of remote control units throughout your residence, you will find this little circuit beneficial. The LED clearly indicates whether the remote control unit is actually emitting infrared light when a button is pressed on the unit. The circuit utilizes a photo-diode (D1) to sense the infrared light released by the remote control unit (if it is functioning correctly). The plastic casing of this diode serves as an infrared filter, being only transparent to invisible light with a wavelength of 950 nm.

Integrated Circuits: Photo-diodes, frequently employed as active components in electronic circuits, are semiconductor devices capable of converting light energy into electrical energy, and vice-versa. These components exhibit a reverse-biased operation, meaning they are designed to conduct current when a voltage is applied in the opposite direction of their intended flow. They are particularly useful in optical communication systems, light sensors, and various other applications where detecting or modulating light is required. Furthermore, their operating characteristics, including sensitivity to light intensity and wavelength, make them ideal for applications where precise measurements of infrared radiation are crucial.

Although there may be remote control units that utilize infrared diodes operating at a different wavelength, the circuit has enough sensitivity to detect them as well. If sufficient light falls on photo-diode D1, an electrical current will flow through the diode. In fact, what occurs is that the leakage current increases, as photo-diodes are generally operated in reverse-biased mode (as is the case here). If the current is substantial enough, transistor T1 conducts and compels LED D2 to illuminate.

If LED D2 remains dark, this signifies that the remote control unit is not generating any infrared light. This could be due to depleted batteries (or batteries) or a defect within the internal circuitry. Careful attention should be paid to the polarization of the photo-diode when integrating it into the circuit. The cathode is clearly marked by a special pin. For LED D2, utilize a low-current type that can handle a current of at least 7 mA. The detector can be powered by a pair of 1.5-V penlight cells connected in series.