The Common Frustration: Unresponsive Remote Controls
We’ve all experienced the frustration of pressing buttons on the TV remote, only to be met with no response. The immediate dilemma arises: is the remote device malfunctioning, or is it simply a matter of replacing the battery? When it comes to testing the functionality of the infrared LED, relying on eyesight alone proves futile. However, there’s a solution at hand: a simple and effective circuit can be constructed to create a handy gadget capable of swiftly and efficiently testing all infrared (IR) remote controls.
Infrared Remote Control Tester Circuit Overview
The circuit primarily consists of a Darlington amplifier stage incorporating three transistors, with the first one being a phototransistor. This combination is highly resistant to changes in ambient light levels. The IR-transistor responds to constant unmodulated infrared light but under this circumstance, a continuous DC current flows across resistors R3 and R2. The voltage divider created by these high-impedance resistors ensures that the subsequent Darlington amplifier (T1 and T2) cannot be activated. The low 3 V supply voltage maintains the voltage on R2 below the Darlington stage’s threshold voltage of approximately 1.2 V (2 x UBE) when the phototransistor is conducting.
Functioning with Modulated IR Signal
The scenario changes significantly when the phototransistor receives a pulse-modulated IR signal, akin to the signals transmitted by the IR-LEDs in infrared remote controls. This pulse train, oscillating between 35 to 40 kHz, travels unimpeded through capacitor C1 to the base of the Darlington amplifier, where it undergoes substantial amplification. Consequently, the LED lights up, indicating the functionality of the remote control.
Pulse Integration and Low Power Consumption
Capacitor C2 integrates the amplified pulse train, allowing the LED to remain visible even for short bursts of the modulated IR signal. It’s noteworthy that the circuit draws an extremely low quiescent current of under 500 nA, ensuring an extended battery life even without an off switch.
Component Selection and Construction Simplification
The selection of components is not highly critical. Virtually any IR-phototransistor can be used for T3, while standard NPN small-signal transistors are suitable for T1 and T2. To simplify the construction process, the author has developed a printed circuit board, complete with the necessary milling data files (GBR and HPGL), which can be freely downloaded from the Elektor website . www.elektor.com/110088