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'[EE]: Strange interference to my simple oscillator'
2006\05\26@000214 by John Waters

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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


2006\05\26@002645 by Marcel Birthelmer

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A lot of people will tell you to go from a breadboard to perf board or
something similar, due to the antenna-like features of the breadboard
tracks. This might have something to do with your circuit.
- Marcel

John Waters wrote:
{Quote hidden}

2006\05\26@015308 by Mark Rages

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On 5/25/06, John Waters <spam_OUTjohn_fm_watersTakeThisOuTspamhotmail.com> wrote:
{Quote hidden}

Can you draw your circuit for us?  Show all resistor values and bypass
capacitors.

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2006\05\26@032738 by William Chops Westfield

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>> 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.

Such circuits are famously susceptible to various outside influences
and the BEAM robotics folk attribute near magic (living-system like)
properties to very similar circuits.  For instance, if you're flashing
an LED at the output, the amount of light shining ON the LED can
change the behavior of the circuit (the BEAM magic consists of
maximizing these outside influences...)

BillW

2006\05\26@062923 by Tom Sefranek

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Is your power source bypassed at the chiip?
Are all inputs terminated in low impedance?  (Ground/Vdd)

John Waters wrote:

{Quote hidden}

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2006\05\26@092431 by Paul Hutchinson

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> -----Original Message-----
> From: piclist-bouncesspamKILLspammit.edu On Behalf Of John Waters
> Sent: Friday, May 26, 2006 12:02 AM
>
> 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
<snip>
>
> 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?

A light turning off or on can create a large amount of electrical noise. The
4000 series CMOS logic family has very high input impedances making them
very susceptible to noise pickup problems.

Decreasing all circuit impedances will decrease the noise pickup problem. Do
this by lowering all resistor values, raising all capacitor values and
decreasing all wire lengths.

If these simple fixes don't alleviate the problem you'll need to hook up an
oscilloscope to see the noise and then figure out an effective shielding and
filtering strategy.

Paul

>
> Thanks in advanced!
>
> John

2006\05\26@203525 by Dwayne Reid

flavicon
face
At 10:02 PM 5/25/2006, John Waters wrote:
>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:-

Did you ever resolve this?

If not, I'd be looking at the input pins of the chip.  Your symptoms
accurately describe what can happen with floating CMOS inputs.  Are
all the un-used inputs tied high or low as needed?

Make sure that you have a small (100n) bypass cap between Vss & Vdd
near the chip.

I've seen a few responses that suggest not using a plastic breadboard
for this kind of stuff.  Nonsense!  Plastic breadboard sockets work
VERY well for this kind of thing.

If you are using large value resistors for any of your inputs, I'd
suggest putting a metal sheet under the breadboard strip and
connecting that sheet to the Vss rail on the breadboard strip.  This
will help keep much of the external noise from influencing the circuit.

dwayne

PS - I routinely debug low level audio designs using not much more
than breadboard sockets sitting on top of a ground plane.  No real problems.

dwayne

--
Dwayne Reid   <.....dwaynerKILLspamspam.....planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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