Infrared Remote-Control Tester Circuit

The infrared remote-control tester uses a sensitive PN-type solar sensor that is connected directly to a Darlington amplifier made up of transistors Q1 and Q2. Biasing is provided by R1 and PI, a variable resistor that serves as a sensitivity control. The collector lead of Q1 is the output lead of the Darlington amp, and it is connected to a red LED and the primary of transformer Tl. The function of Tl is to convert the low-voltage output signal to a level high enough to drive a small piezo disc. That disc makes a clicking sound when the sensor picks up an infrared signal that is varying in frequency or amplitude.
Infrared Remote-Control Tester Circuit - schematic

The infrared sensor will also pick up visible light. The use of an IR filter (Wrat- ton #87) is recommended.

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