9V power supply problem

Thread Starter

brozizds

Joined Aug 15, 2010
135
ty for your responce I am not using batts. I'm using a 9V power supply at 800 m Amp. to power 8 of these timers. I have tried to isolate them by wiring 8 diff. leads on pos. and neg sides but the timers still go off when I start another. Thanks:( PS I have powered one of these timers with 9V @ 9m Amp
 

mtripoli

Joined Feb 9, 2010
44
What do you have for decoupling on each circuit? I'd try putting a big honking (technical term) electrolytic across pins 1 and 8. If you're getting some kind of ground bounce or spike on Vcc it could be resetting the 555. Something like 100-470uF...

Mike T.
 

retched

Joined Dec 5, 2009
5,208
Are you using decoupling/bypass caps? If you are not, the switching action of the timers and the powersupply could cause the timers to go awry.

http://forum.allaboutcircuits.com/showthread.php?t=45583&highlight=decoupling+cap

Adding a larger cap across the powersupply pins will help keep the power from sagging.

This sag will trigger the 555s

Are you building this EXACTLY as shown? No changes? no "I didn't have that, so I used this in stead"?
 

Thread Starter

brozizds

Joined Aug 15, 2010
135
Thanks Guys , Maybe this will help. I am using the circuit I hyperlinked on my first entry but also some of this one ( adding a variable resistor)http://www.kpsec.freeuk.com/projects/timer.htm, with Bill Marsdens help I did get all eight timers working perfectly as I need them . I started an earlier thread on 9V power supply to find out how many mA I would need to power all 8 timers from one wall wart and 800 mA does fine, but as you can see in this tread I'm having Probs.(Please keep in mind I'm a 58 yr. old newbie) so if someone can help I would appreacate it ! Do you guys need any more details? Thanks Jim
:)
 

SgtWookie

Joined Jul 17, 2007
22,210
As has already been mentioned at least twice, you need bypass/decoupling capacitors across the power supply and across each 555 timer IC.

For 555 timers, pin 1 is Gnd and pin 8 is Vcc. You need to connect a 0.1uF capacitor across these two pins on every timer. This means you need eight additional 0.1uF caps.

You also need at least one electrolytic cap across your 9v DC supply, somewhere in close vicinity to your board.

Please review this thread: http://forum.allaboutcircuits.com/showthread.php?t=45583

Long interconnecting wires will cause problems, as they are inductive; the longer the wires, the greater the inductance. You should keep your wires as short as possible.
 

Thread Starter

brozizds

Joined Aug 15, 2010
135
Tx. Sgt.Wookie,
would you have an idea on what μF I would need for the power supply E caps? And will I need 8 of them 1 for each board? Thanks again Jim
 
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Kermit2

Joined Feb 5, 2010
4,163
You need eight small ones .1 or 1.0 uF for the timer IC's, and one large one for the power rails

Almost any value would work for the power rail cap. Preferably something larger than 1 uF. I would suggest anything with three digits . (100uF to 680uF)

Check and be sure it is rated for more than 9 VDC. Some small caps are rated 6 volt. A RAdio shack store would be a good place to look. I think they have an electrlytic 'grab bag' for 7.95 or something like that.
 

SgtWookie

Joined Jul 17, 2007
22,210
I didn't know you had individual boards.

Each 555 timer will then require a minimum of a 0.1uF (100nF) capacitor, metal poly film or ceramic, across the Vcc/GND pins, and you will need at least one electrolytic cap per board. 100uF to 470uF would likely be OK.

If you have long interconnecting wires, that could be a problem, as they will "ring" or oscillate at high frequency for a period of time after the 555 output changes states.

It would help a great deal if you could post (a) photo(s) of your project.
 

SgtWookie

Joined Jul 17, 2007
22,210
Brozizds,
You attempted to post an image that's in your E-mail account. You're the only person that can see it.

Please edit your post, delete the link you put in, and then click the "Go Advanced" button at the bottom.

Then click the "Manage Attachments" at the bottom of the next screen. Upload the image from your computer's disk drive.
.jpg images are OK for photos. .png images are preferred for schematics.
 

Wendy

Joined Mar 24, 2008
21,906
Sorry about that guy, I should have mentioned that on the other threads.

You need a filter cap on every board, close to the 555. Something like this should work, you may be able to get rid of the resistors. The idea is suppress the pulses between the units, and the exact values of the caps aren't that critical (as long as they are large). One problem you may run into though, really large caps can overload your wall wart (if that is what you're using). What did you end up with anyhow?

 

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Thread Starter

brozizds

Joined Aug 15, 2010
135
Bill,
Thanks for the sketch and I am using a 9V 800mA wallwart. When I was testing each board I was using a 9V batt. eliminator @ 9mA and it worked fine on single board app. Thank you again been a while Jim
PS. Do you think I will have to increase mA with the additional load?
 

Thread Starter

brozizds

Joined Aug 15, 2010
135
Thanks Guys, I installed the caps on all the boards and they all work perfect! Thank you again, Jim;)
PS. And thanks from my brother in law @ Unkle Bucks BBQ Pit!
 
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