Here is an Infrared transmitter circuit for emitting pulsed IR rays with a frequency of 4.5kHz for Phototransistor based receivers. The range of the IR transmission is around 1 meter. Unlike 555 IC based IR transmitters, it uses the Phase Locked Loop (PLL) IC as an oscillator. Phototransistors are more responsive to Pulsed IR rays than direct light.
Only the VCO (Voltage Controlled Oscillator) part of the PLL IC NE 567 is used to generate oscillations with a frequency of 4.5 kHz using the components R1 and C3. T1 is the driver transistor for the IR LED and R3 limits LED current.
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