[sdiy] 555 osc lock-up???THANKS!

[peter edwards]

Well it seems to be working! I'm using an L555CP which I'm pretty  
sure is NOT low power... I'll see if it's even better with the 7555.  
Then I have a 220ohm resistor to power and a 10uF &.1uf decoupler  
from + to -. Does the trick.... Only locks ONCE in a while. More  
often at higher frequencies. The frequency drifts a little, but my  
studio is pretty cold... that might have something to do with it.
I wish I could show you what I'm working on. I'm running two square  
waves at close frequency. If you add the two signals together through  
an AND gate you get a 50%-100% duty cycle modulating square wave  
output. If you run the two waves into an XOR gate it gives you a  
perfect 0%-100% duty cycle modulation. I'm using that to pulse a high  
intensity LEDs (1WATT) as well as outputting a phasing audio drone.  
next level brain games.
Thanks for the help!
-pete
www.casperelectronics.com

On Dec 29, 2009, at 7:17 AM, Scott Gravenhorst wrote:

> "George Hearn" <georgehearn at btinternet.com> wrote:
>> I'd agree with all the responses, to avoid lock up, and un- 
>> necessary noise
>> coupling via the power rail:
>>
>> 1. Use CMOS 555's (7555?)
>
> 7555 is the correct number, tho sometimes there are letters in  
> front of 7555.
>
>> 2. Small impedance in the power supply path of 555 each chip,  
>> could try
>> 100R, with large 10u and small .1u decoupling for each chip  
>> separately.
>
> The 100R resistor can be replaced with an LED.  LEDs work better  
> than small signal
> diodes for this.  The performance is a bit better than a 100R  
> resistor.
>
>> 3. Separate ground returns.
>>
>> I don't tend to use 555's for exactly the problems you are  
>> having.  They
>> have a tendency to talk (shout) down your power rail!  George
>>
>> -----Original Message-----
>> From: synth-diy-bounces at dropmix.xs4all.nl
>> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Paul Perry
>> Sent: 29 December 2009 12:44
>> To: synth-diy at dropmix.xs4all.nl
>> Subject: Re: [sdiy] 555 osc lock-up???
>>
>> Yes, using CMOS 555s will help, and separate power supplies.
>> But in the absence of separate supplies, it might be worth trying to
>> decouple the 555 circuits from the rest of the circuit and each other
>> by running the power to them via a 220 ohm resistor with a .1
>> ceramic and 10u electro bypass on the 555 side.
>>
>> Also, the coupling may well be (probably is!) via a shared ground
>> return for the two 555 sections.. try to get a direct path back to  
>> the
>> power supply ground for both of them.
>>
>> paul perry Melbourne Australia
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>
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