[time-nuts] Interesting Patent

Normand Martel martelno at yahoo.com
Wed May 17 22:05:47 EDT 2006


I remember having seen an interesting analog
counter/frequency divider using charge pumps and
unijunction transistors in a watchmaker's mechanical
watch adjusting machine. ( i don't remember the
machine's name, but it is used to adjust the
oscillator's (balance wheel/hairspring) frequency.

The interesting part was that the unijunctions worked
in a charge pump fashion rather than an RC time
constant fashion. This way, at least theorically (i
never tried it), the counter could be used with a
variable frequency source.

The principle is simple: The unijunction transistor is
used in it's traditional relaxation oscillator
circuit, except that there's no pullup resistor
between the unijunction's emitter and supply line. The
Emitter-ground capacitor is charged by another
(smaller) capacitor through a series diode an a
calibrated voltage pulse. This way, at each input
pulse, the capacitor is charged with a fixed
(predetermined) voltage increment. After 'n' pulses,
when the emitter reaches the discharge voltage, the
UJT fires and sends an output pulse. (If one watches
the emitter voltage with a scope, he will see a
staircase waveform).

The interesting part is that the voltage increment
remains fixed, regardless of the pulse's duration or
frequency (up to a certain extent...).

I know, it's hard to describe the circuit with words,
but if i find the schematic, i'll find a way to send
it here.

Have a good day!

Normand Martel
Montreal, Qc. Canada

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