Are you using the same saltwater? =A0I was thinking it could possibly be ev=
aporation in addition to the things already mentioned.

----------------------------------------
> From: bobblick@ftml.net
> To: piclist@MIT.EDU
> Subject: Re: [EE] Oscillator stability
> Date: Tue, 9 Sep 2014 20:32:54 -0700
>
> Temperature difference between morning and evening. What sort of timing
> capacitor are you using? That's the low-hanging fruit. Lots of things
> influence the frequency in a 555 circuit. Power supply voltage, of
> course. Next in line is if the discharge current is high it'll be
> somewhat temperature sensitive. Also if you have changed the divider
> voltage(pin 5 I think) from its normal 2/3 Vcc it becomes voltage
> sensitive. That all assumes the standard oscillator circuit.
>
> But the capacitor is the first place to look.
>
> Friendly regards, Bob
>
> On Tue, Sep 9, 2014, at 08:14 PM, Ravi wrote:
>> Hi Guys,
>>
>> I have a 555 based oscillator, AC couple and the probes are in salt
>> water of a given concentration.
>>
>> The probes are in water for about 1 hour from 8 PM to 9 PM and the
>> reading is 6500 Hz. I switch off the unit.
>>
>> The next day at 9 AM in the morning I see that the value has changed to
>> 7000 Hz.
>>
>> What could be causing the drift?
>>
>> Cheers
>>
>> Ravi
>
>
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