Why cap needed at Schmitt output?

cross the two ICs but the crucial step appeared to be implementing the sugg estion made by several of you to place a small cap across the 10M feedback resistor. Used 2200pF and now toggling cleanly. Hope this survives final co nstruction!

CMOS device getting "touched" by human hands? Hmm... I urge you to also add input protection. Two 1N914 or 1N4148 diodes. Connect D1 from your Input t o V+ (D1 anode at Input), and D2 from Input to Ground (D2 cathode at Input) . Put a series-R, like 100k, in front of this Input node, to create new Inp ut node. If RF interference is a problem, try adding a 'small' cap across D

-RS

I've never actually used those myself, but I'm tempted to make up some boards that are:

- 5cm * 5cm - one side groundplane - other side sea of pads as in

And then make them available for anyone to buy via dirtypcbs for $15 for ~10 boards.

IME I have seen actual Schmitt ICs (74xx14, 74xx132, etc.) have this exact problem when used as a RESET circuit of a microprocessor / microcontroller.

The fix was a series 10K-47K resistor between the RC and the input of the Schmitt gate.

You have a large input resistor on the first NOR (neither gate is a Schmitt) but you could try a series resistor before the second gate.

I can't explain why a chip specifically designed to square-up slow rising / falling signals has this burst problem but I can state that I have seen this series-resistor-fix on other designs that were not my own.

I'd buy some.

Cheers

Phil Hobbs

itead will make 10x 5x5cm 2layer boards for $9.99 and give you two extra for free if you let them use the design to sell boards to other for a few $

this (with some random pads and grid size) took 2 minutes in kicad,

-Lasse

I, also.

I used dirtypcbs to make up a couple of sizes of Manhattan-style sea-of-pads boards, sorta like this, but intended for tacking down through-hole analog components rather than ICs. I used larger pads, with some ground plane in between each quad of four pads (stitched through to the bottom ground plane with vias), and some connection pads and power traces along the upper and lower edges.

Doing it consistently involved figuring out how to add pads and traces and vias to a KiCAD layout programatically (via a perl script) and then doing the ground-fill on the result.

They turned out just fine... and the dirtypcbs.com price was excellent.

are you blocking google groups?