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

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

Follow Ups:

  90% solved... Mike   Posted at: 08/07/02 (0)

  circuit diagram sa.v   Posted at: 08/06/02 (1)

  Schematic isn't drawn yet Mike   Posted at: 08/06/02 (0)

  Re: How Can I Produce a Triggerless One-Shot? Mike   Posted at: 08/06/02 (6)

  Re: How Can I Produce a Triggerless One-Shot? David Ashby   Posted at: 08/06/02 (5)

  R-C circuit didn't work Mike   Posted at: 08/06/02 (4)

  Re: R-C circuit didn't work David Ashby   Posted at: 08/09/02 (3)

  umm, Schmitt what? Mike   Posted at: 08/09/02 (2)

  Re: umm, Schmitt what? David Ashby   Posted at: 08/12/02 (1)

  Off to get a Schmitt trigger chip... Mike   Posted at: 08/12/02 (0)

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