If you need assistance, please send an email to forum at 4hv dot org. To ensure your email is not marked as spam, please include the phrase "4hv help" in the subject line. You can also find assistance via IRC, at irc.shadowworld.net, room #hvcomm.
Support 4hv.org!
Donate:
4hv.org is hosted on a dedicated server. Unfortunately, this server costs and we rely on the help of site members to keep 4hv.org running. Please consider donating. We will place your name on the thanks list and you'll be helping to keep 4hv.org alive and free for everyone. Members whose names appear in red bold have donated recently. Green bold denotes those who have recently donated to keep the server carbon neutral.
Special Thanks To:
Aaron Holmes
Aaron Wheeler
Adam Horden
Alan Scrimgeour
Andre
Andrew Haynes
Anonymous000
asabase
Austin Weil
barney
Barry
Bert Hickman
Bill Kukowski
Blitzorn
Brandon Paradelas
Bruce Bowling
BubeeMike
Byong Park
Cesiumsponge
Chris F.
Chris Hooper
Corey Worthington
Derek Woodroffe
Dalus
Dan Strother
Daniel Davis
Daniel Uhrenholt
datasheetarchive
Dave Billington
Dave Marshall
David F.
Dennis Rogers
drelectrix
Dr. John Gudenas
Dr. Spark
E.TexasTesla
eastvoltresearch
Eirik Taylor
Erik Dyakov
Erlend^SE
Finn Hammer
Firebug24k
GalliumMan
Gary Peterson
George Slade
GhostNull
Gordon Mcknight
Graham Armitage
Grant
GreySoul
Henry H
IamSmooth
In memory of Leo Powning
Jacob Cash
James Howells
James Pawson
Jeff Greenfield
Jeff Thomas
Jesse Frost
Jim Mitchell
jlr134
Joe Mastroianni
John Forcina
John Oberg
John Willcutt
Jon Newcomb
klugesmith
Leslie Wright
Lutz Hoffman
Mads Barnkob
Martin King
Mats Karlsson
Matt Gibson
Matthew Guidry
mbd
Michael D'Angelo
Mikkel
mileswaldron
mister_rf
Neil Foster
Nick de Smith
Nick Soroka
nicklenorp
Nik
Norman Stanley
Patrick Coleman
Paul Brodie
Paul Jordan
Paul Montgomery
Ped
Peter Krogen
Peter Terren
PhilGood
Richard Feldman
Robert Bush
Royce Bailey
Scott Fusare
Scott Newman
smiffy
Stella
Steven Busic
Steve Conner
Steve Jones
Steve Ward
Sulaiman
Thomas Coyle
Thomas A. Wallace
Thomas W
Timo
Torch
Ulf Jonsson
vasil
Vaxian
vladi mazzilli
wastehl
Weston
William Kim
William N.
William Stehl
Wesley Venis
The aforementioned have contributed financially to the continuing triumph of 4hv.org. They are deserving of my most heartfelt thanks.
Registered Member #1940
Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34
Dear all,
I’m working on a pulse delay circuit. It should delay a pulse that comes from a mechanical switch. The mechanical switch is grounded at one side. I can’t change that.
I found a pulse delay schematic on the internet. I modified it so it would work for me. This is how it works.
Mechanical switch closed: output LOW Mechanical switch opens: after a defined amount of time the output goes to HIGH
The whole idea works fine. But there is one problem. When the mechanical switch closes the output should go to low. But occasionally it doesn’t. It starts to switch between high and low at a really high frequency. I have no idea where it is coming from. Can you help me out?
Registered Member #1940
Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34
I have done some test. And the solution works! But there is a downside. The new capacitor creates a pulse delay of its own. I have done some test with a 10nF capacitor. This capacitor eliminates the strange output signal and it is so small that it does not seem to influence the pulse delay that much. I will do some further test when my pulse create circuit is working again.
The switch starts closed and the output is low. Then the switch opens. The output goes to high after a curtain amount of time. Then the switch closes again and the output should directly go to low. But sometimes the output starts to resonate between high and low at a frequency of 3.3 MHz. The resonation doesn’t stop until the switch opens again.
I have changed various resisters hoping to solve this problem. The only thing that happened was that the resonation moved to another frequency. I also had to change the input voltage to get it to resonate again.
This thing is driving me nuts! Please help me out
Edit: At this point I’m trying random things to stable this circuit. I may have found one. I’m not using pin 7 (discharge). So I randomly decided to place a capacitor between pin 7 and the ground. A 1 nF capacitor seems to work best. And it stables the circuit! Does this make any sense?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
Have you got capacitors (e.g. 100uF electrolytic + 100nF film or ceramic) from 0v to +12v ? Strange things happen without proper supply bypass/decoupling etc. especially with long power supply leads. Also, 10uF from the Control pin to 0v is a good idea (usually)
The 1nF from discharge pin to 0v doesn't make sense to me at the moment; unless you're using stripboard (Veroboard in uk) or similar prototyping method and there is capacitive coupling across the tracks.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
he may need to devise a schmitt trigger or use one from an IC, so he can minimise the propagation delay, given the capacitor idea shows some improvement, though an undesireble result (the delay) occurs.
This site is powered by e107, which is released under the GNU GPL License. All work on this site, except where otherwise noted, is licensed under a Creative Commons Attribution-ShareAlike 2.5 License. By submitting any information to this site, you agree that anything submitted will be so licensed. Please read our Disclaimer and Policies page for information on your rights and responsibilities regarding this site.
555 timer problem
