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From: Kevin McMurtrie
Subject: Re: how to reduce noise from 555 timer...???
User-Agent: MT-NewsWatcher/3.2 (PPC Mac OS X)
Date: Fri, 20 Dec 2002 21:49:18 GMT
NNTP-Posting-Date: Fri, 20 Dec 2002 13:49:18 PST
In article ,
"Phil Allison" wrote:
>"Kevin McMurtrie" wrote in message
>> Is your timer capacitor an electrolytic? You better open up your
>> electronics book and read up on them.
>They are constantly shorting and
> ** Can you provide a reference for this ???
Find a ~100uF capacitor that hasn't been powered up in a while. Try to
charge it through a 1M resistor. It won't charge or it will hesitate at
certain voltages. Charge up the capacitor with a higher current and
leave it charged for a while. Now discharge and repeat the 1M test.
Now it charges smoothly.
I found a reference to it:
They're fine for many audio applications but they will not operate an
oscillator at a constant frequency, especially if the current is low.
Add to that the temperature and age drifts and you definitely have the
wrong component for a precision timer.
>They're no good for low current use and they're worst
>> you could pick for a critical instrumentation component.
> ** Electros have some leakage current but that does not make them all
> Plenty are used in low current situations without problem.
> For instance the input cap of a low Z mic pre-amp.
> ................. Phil
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