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Subject: Re: How Can I Produce a Triggerless One-Shot?

Date: 08/06/02 at 7:56 AM
Posted by: David Ashby
E-mail: dashby@quin.co.uk
Message Posted:

In Reply to: How Can I Produce a Triggerless One-Shot? posted by Mike on 08/05/02 at 11:02 PM:

Hello Mike,

You can make a simple power-on reset generator as follows:

1) Connect a resistor from the RESET pin to 0V.

2) Connect a capacitor from the RESET pin to the positive supply rail.

3) Connect a diode (1N4148 or similar) with the anode to 0V and the cathode to the RESET pin. This diode is in parallel with the resistor.

On switch-on, your RESET pin will initially be taken high as the positive supply rail voltage rises. Then, as the capacitor charges via the resistor, the reset pin falls towards 0V and your circuit can begin to operate. The reset delay depends on the threshold at the RESET pin, but will roughly be about half the R-C time constant of the resistor and capacitor. The diode allows the capacitor to discharge quickly when the circuit is powered down, ready for when you switch on next time.

Hope this helps

David Ashby

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