TRANSMIT_TIME_LIMITER

Published:2009/7/11 0:51:00 Author:May | From:SeekIC

This circuit prevents making transmissions that are too long, which time out repeaters and/or tie up a communications channel too long. On transmit, the PTT (push to talk |ipe) from the microphone is at ground. This causes one input of the AND gate (4081) to go high. The 555 is held in the reset mode. An MC1453B monostable multivibrator generates a pulse to the 555 and causes it to produce a gate of length approximately 1.1RC, where R is selected for desired time delay and C is 100 μF. The output of pin 3 of the 555 causes the 4081 gate to go high, turns on Q1, and keys the transmitter. At the end of the cycle (1.1RC), the AND gate will lose one input, which turns off Q1 and unkeys the transmitter.



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