Frequency multiplier - low frequency module for counters

single channel infra-red remote control frequency multiplier elektor january 1982 — 1-53 from the transmitter are detected by the infra-red photo diode, Dl. The cathode connection of this device (BP 104) is marked either by a blue dot or by a little "bump". The photo diode is biassed by means of resistor R1, the value of which has been chosen such that oper- ation of the diode is "favourable" under normal (ambient) lighting conditions. The following amplifier stages, con- structed around transistors T1/T2 and T3/T4, amplify the input signal by a factor of 80 dB (= 10,000 times). Nega- tive feedback is supplied via resistor R8. The amplified output signal appears at the collector of T4 and is rectified by diodes D2 and D3. Every input pulse (20 kHz) causes an increase in charge across capacitor C6. The rate of charge is dependent on the relationship between capacitors C5 and C6 as well as the amplitude of the output signal. Transistor T5 will conduct as soon as the voltage across...