I started with vacuum tubes (valves?) and it took me a while to understand 
that CMOS were voltage operated devices like tubes, while TTL are current 
operated devices.  So a CMOS oscillator is possible.

But looks to me like you are supplying the wrong feedback to the circuit. 
Assume input to gate one is positive, output gate one (input gate two) will 
be negative, then output gate two (input gate one) is positive.  The 
positive feedback should insure that it things never change.  You should use 
a odd number of inverters to get the negative (opposite polarity) feedback 
to cause oscillation.  You can also add resistors and capacitors to delay 
the negative feedback which will change the frequency.

So do not think you have a oscillator now but some kind of a detector that 
oscillates when it detects (or not).  It may be detecting EMI (electro 
magnetic interference) or RFI (radio frequency interference) from computer 
or 60 cycle hum from florescent lighting or house wiring.  Don't think it is 
detecting light as such.

Bill

----- Original Message ----- 
From: "John Waters" <john_fm_waters@hotmail.com>
To: <piclist@mit.edu>
Sent: Thursday, May 25, 2006 9:02 PM
Subject: [EE]: Strange interference to my simple oscillator circuit


> Hi All,
>
> I encountered some strange problems when was doing experiments on a simple
> oscillator circuit. I built a circuit that was made up by the 4 COMS NOR
> gates in a CD4001. I used the first 2 NOR gates to build a simple 
> monostable
> that turned on or off a low frequency oscillator made up by the 3rd and 
> 4th
> NOR gates. The circuit was built on a breadboard, running on 6V batteries. 
> I
> found the following strange things happened and could not explain why:-
>
> 1. when I turned on my computer nearby, the frequency of the oscillator
> changed (slightly though). When I turned off the PC, the frequency went 
> back
> to normal.
>
> 2. I triggered the monostable manually so that the output went to the ON
> state, but when I switched the light in the room off, at that particular
> moment, the monostable went back to normal state automatically.
>
> It was obvious that my simple circuit was interfered, but I was using
> battery as the power source, there was no way the mains spikes could go to
> my circuit! Could somebody give an explaination and suggest how to make my
> circuit not susceptible to the interference?
>
> Thanks in advanced!
>
> John
>
>
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