Archive of the former Yahoo!Groups mailing list: MOTM

On the VC Pulse Divider from Serge, there is an output called 'STEPPED'. I'm
am pretty sure
how they did it (not seeing the circuit).

The output is a stair-cased, positive-going sawtooth. The sawtooth is
generated by a 5-bit
counter, that is ∗clocked∗ by the input pulses and ∗reset∗ by the
divide-by-N pulse.
The output counter bits feed a 5-bit DAC.

So, here are some interesting things about this sawtooth:

a) for a fixed frequency in, the ∗amplitude∗ is inversly proportional to the
divide ratio. Think
about it: the longer you count, the higher the amplitude.

b) of course, for a fixed input frequency, the ∗output∗ frequency is
proportional to the divide
ratio. If you input 4Khz and divide by 8, you get out a 500Hz sawtooth with
8 steps. Assuming
a -5V to +5V output scaling (like all the other signal generators), we have
10V/32 steps = 312mv/step. So for 8 steps = -5V to -2.5V sawtooth.

For straining the brain more: this acts as a low-pass filter! Since the
divide ratio is a control
voltage, then if the input is fixed (say 2Khz) then as the divisor is swept
from 32 to 1 the
amplitude AND frequency change. But, the amplitude drops off at higher
frequency outputs
since the counter is reset faster and faster.

Of course, if you fix the divide ratio and sweep the input, the amplitude of
the sawtooth is ∗constant∗
at the divide ratio X 312mv.

Will add $15 to the cost of the module. Discuss!

Paul S.