[sdiy] 555 osc lock-up???

[George Hearn]

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?)
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.
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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