[sdiy] lowpass gate etc - the sounds of capacitors

[Harry Bissell Jr]

Ahhh... My frequency counter is broken :^P

(want to fix it ?)

H^) harry

--- mikei at marketbridge.ca wrote:

> No scope involved... unless you want it to be  :D
> 
> The capacitor is used as the timing cap in a CMOS
> 555 astable. A 
> frequency counter is used to measure the pulse
> repetition rate. It is 
> possible to set the CMOS 555 up for 50% duty cycle -
> or you can hook up 
> a CD4013 to the output to get precise 50% duty cycle
> (in case your freq 
> counter is finicky about duty cycle).
> 
> Good for relative measurements eg. matching...
> select the caps that put 
> out the same Hz (or measure period if you want).
> With an assortment of 
> 1% caps on hand for calibration checking you can get
> a good estimate of 
> the actual capacitance value - taking into account
> the pin capacitance 
> of the CMOS 555 and capacitance of the wiring etc.
> Cheers, Mike
> 
> 
> Harry Bissell Jr wrote:
> > 
> > You'll need a real accurate timebase on your scope
> > to resolve the pulse width.
> > 
> > The bridge mode 'might' be more accurate...
> > 
> > H^) harry
> > 
> > --- mikei at marketbridge.ca wrote:
> > 
> > > "555" timer with frequency counter approach is
> good
> > > but use a CMOS 555
> > > timer instead (such as TLC555  TS555  ICM7555)
> as
> > > the CMOS unit
> > > operates with much smaller leakage currents,
> giving
> > > less error with
> > > smaller capacitances than the more pedestrian
> > > bipolar 555. Have some 1%
> > > polystyrenes on hand for a calibration check.
> > > Mike
> > >
>