Thus, upon the appearance of an IR beam, Bz1 will sound and D3 will light up in a rhythm given by the time constant R8XC2. The current through the LED D3 is limited by R12. In the collector of Q5 is the buzzer Bz1 in parallel with D3. Q4 is a common collector amplifier and Q5 a common emitter amplifier. These pulses discharge C2 when Q2 is saturated, so that when Q2 is blocked again C2 will charge through R8.The phenomenon repeats with a frequency that depends on the C2XR8 time constant. Q3 works as a common collector amplifier, in its emitter having (when there is an IR beam) pulses with an amplitude of 12V. Q1 and Q2 form an amplifier with high amplification, several thousand. When diode D1 (BPW41) receives an IR beam, voltage pulses of tens.hundreds of microvolts appear at its terminals.This depends on the intensity of the IR beam and the distance from which it comes.īecause the blocking point of the transistors is chosen to be very close to their normal active region, the appearance of voltage pulses causes the transistors Q1, Q2 to work as amplifiers in common emitter connection.įrom an alternating current point of view, the emitter of Q1 is grounded through C1. 30uA at 12V), which allows a long battery life, even in the conditions where there is no a power supply voltage switch. This means a very low current consumption from the source power supply (approx. In the conditions that the BPW41 type IR optical transducer does not receive an IR beam, the static operating points of the circuit are calculated in such a way that D1, D2 and all transistors Q1.Q5 are blocked.
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