Holds the transmitter active a little longer than the input duration
|RPT TX hold circuit|
This device is intended to operate with "Active Low" logic, where the input and output levels can be anything between TTL 5v levels, or full 13.8V signals. This is done by using discreet transistors for the input and output.
The TLC272 op amp is used as a comparator, with an R/C time constant ckt for the timing element. The idea is to use it to deley when a repeater drops its carrier after the incoming signal drops. A 555 ckt wouldn't work. The input signal can stay low for some time. The 555 still "times out" and will go high almost as soon as the input does. This circuit will hold the output LOW indefinitely, and will then start timing as soon as the input goes high. It is very reliable and virtually foolproof.
|RPT delay ckt schematic|
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