[CingKrab]

Hi all:
Sorry for the off-topic post, since this isn't audio related. I'd appreciate any help from you guys though.

I've built something like this:

http://www.discovercircuits.com/PDF-...F/ONESHOTS.pdf

on both a breadboard and a protoboard. However, only on the protoboard, there is a short spike on the output when the power is turned on. It is rounded. The oscillator works properly after the power is on. However, the output is hooked up to a flip-flip ring counter, and this spike causes the ring counter to start earlier than I want, which kind of screws up my whole circuit. Without this problem, the circuit works perfectly on the breadboard. I do not see the spike on the input (and anyways it should be a fairly square pulse on the output
if there's is an input pulse). What can cause a spike like this?

 

[amb]

Do you have a decoupling capacitor next to each chip? If not you should. Maybe the inductance in the lines/wires of the power/ground wiring is glitching.

 

[CingKrab]

I do have a 0.1 uF cap next to the Vdd pin of every chip I'm using. Is that big enough? I don't know anything about the inductance though. It is, however, the closest chip to the power/ground lines.

 

[amb]

0.1uF next to each chip should be enough; oh well, that was a shot in the dark.

 

[CingKrab]

So does anyone have any ideas? I'd appreciate any input you guys might have.

 

[rickcr42]

sounds like "bounce" from the mechanical PB Switch

Check out some debounce circuits

 

[stackofhay]

You might consider adding a classic power up reset circuit to your board, so the ring counter and other elements remain in a reset state until the power rails come up to valid levels.

During the time the power rails are slewing, it's hard to predict the exact behavior of the circuit, so it's best just to keep everything reset until the rails have stabilized to a level that is in the spec'd operating range for the parts used in the circuit.

... just a thought