I'm trying to modify a circuit where a tone detector is sending a signal to another device that will read this output as a simple Boolean signal. The problem is I want the tone detector to read the signal for like 15-20 seconds to eliminate the chance of it reading random noise interference. What would be the best way to implement this? Some type of setup with a capacitor storing the charge and then dissapating after a certain amount of time (maybe with a schmitt trigger, comparator, ?).
Kris.
The NE567 tone decoder can detect a tone buried in noise. You can connect an output filter capacitor to pin 1. This prevents false triggering, and dropouts; but it introduces output chatter. The chatter could be removed by a monostable, if required. Alternatively, the chatter can be eliminated by applying positive feedback between pins 8 and 1. See the datasheet for details:
Thanks Andrew.
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