AW: [sdiy] Sequ... (mistake!)

[Czech Martin]

> http://www.ersatzplanet.com/Divide-by-n.gif

The basic idea is quite clear. 
The nice thing is that it will work down to DC
(no leakage). OTOH the 741 is not particular fast,
the higher end will be limited by this (748?, 311?,
watch out for max. diff. voltage spec of op amp).

But I do not understand a few things.
First of all: no hysteresis for the 741.
You can certainly find positions of the pot where
the system is therefore unstable, or in other terms:
A slow ramp on the control input (voltage) will
give different divisors, as expected, but noise
at the thresholds.

The second problem is that I do not understand how the DAC
works. The counter outputs (synchronous counter?, glitches?)
are connected via resistors and drive a high impedance
pin of the 741. So, basically no current flow...,
ahh , I see, the current flow takes place BETWEEN the counter bits.
Oh well, may work for 8 Bit. Otherwise R2R is also an option
for the diyer.

Maybe there is a glitch problem during count transitions.
741 hysteresis will cure this to some extend, could also
make problems at the transitions. 

Note: I do not claim that this circuit doesn't work.
But perhaps the circuit was not intended for divider sweeps.
Perhaps the slowness of the 741 buries a lot of the
mentionend problems, so it works miraculous like a charm,
and problems will come up as soon as the circuit is improved
by faster components?

m.c.