Power-on reset

and remain that way until power-off.

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low and remain that way until power-off.

How does a spare inverter gate, plus an R, a C, and a diode sound? (View in fixed font or M$ Notepad):

` VCC VCC ` + + ` | | ` .-. | ` R| | - D ` | | ^ 1/6 74HC14 ` '-' | ` | | |\\ Reset Pulse ` o----o-----|H>O----o ` | |/ ` C--- ` --- ` | ` | ` =3D=3D=3D ` GND created by Andy=B4s ASCII-Circuit v1.24.140803 Beta

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Positive going pulse width (one and only one pulse at turn-on) will be a little less than R*C seconds. The schottky diode is actually optional if you have a linear supply that discharges slowly at turn-off.

This is just about the simplest reset pulse you can get. Remember that this requires a gate with schmitt trigger input hysteresis to get a clean reset pulse at turn-on. If you've got a spare NAND gate on board, try using a 4093 schmitt trigger NAND gate instead of a standard NAND gate IC. But if a reset pulse with slow fall time is OK, you can just use any inverter gate (or a NAND or NOR set up as an inverter).

If this doesn't do the job, describe your requirements. There are many power watchdog/monitor ICs that can do the job for you with equal simplicity (although they cost more). Do you need brownout protection, too (reset asserted if power supply goes below a certain voltage)? If so, one of these ICs or a comparator would be a better choice.

Good luck Chris

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Is there a relatively simple circuit which can assert a power-on reset. In other words, the line will go high briefly at power-on and then = switch low and remain that way until power-off.

Any ideas would be appreciated.


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