[sdiy] CMOS counter abnormalities

[harrybissell]

another CMOS oddity...

If the Vss supply is missing and at least ONE input pin is tied low,
it will function 'ok' because the input protection diode will supply
the missing 'ground' although the low level will be .7V, not zero.

If all the inputs go high, it will STOP working. :^P

I founf this the hard way, making an octave divider that mysteriously
stopped working when the counter went all ones...

H^) harry

René Schmitz wrote:

> Hi Karl,
>
> Karl Ekdahl wrote:
> > Hi list... i've been working on a analog sequencer for
> > a little while now and discovered that all my 4029
> > behaves really weird. First of all, they need a
> > decoupling cap to CP in to work at all, really strange
> > since my clock source is +-15v (i did cut the negative
> > part using a diode and a pull-down). Second, all
> > outputs give the same frequency out; the same as CP
> > in. Third, the outputs has the same waveshape as my
> > input wave, i.e. if i try to drive the chip with a
> > triangle, the outputs are triangles....
> > I guess *all* of my 4029 somehow magically broke at
> > one instance... ?
>
> Check your supply connections. This sounds suspiciously like Vdd or Vss
> are not connected.
>
> Cheers,
>   René
>
> --
> uzs159 at uni-bonn.de
> http://www.uni-bonn.de/~uzs159