Electronics > Beginners

transistor flip flop

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Boschi:
i have a 32khz signal, and i want to divide it without using any IC.
tha final goal is to have a fully discrete clock.

i found this:
 

which does exacly what i want to do, the only problem is that it works with 60hz and with +12V and -6V, while i want to make it work at 5V.
in the past few days i tried toying a bit with the circuit, but im not able to make it work.

i attached the modified circuit.

the signal that clock the circuit is a 32khz impulse, i tried with a pulse duration of 2us, 1us and about 300ns but the circuit wont change state, it remains always the same.

also, while i understand how it works, i dont understand what resistors are influencing the time costant, just R42/43 or also R40/41?

Kleinstein:
The main resistors to effect the time constant should be R42 and R43. However there is a certain ration of R42/R40 and R43/R41 needed. The ration of 10 looks about good. So the main adjustment of the time constant to the lenght of the trigger pulse would be the capacitors.

The circuit should be OK to run with +5 V instead of 12 V. The trigger pulse may need a slightly negative voltage to really turn of the transistors. One could get this with AC coupling the trigger pulse. Alternative one could use a diode or similar to shift the emitters up a little.
The rising slope of the trigger signal should also be fast enough.

In the hand drawing the resistors parallel to the caps should be larger. I would consider some 2-3 K the minimum.

iMo:
For example

Zero999:
A link to one I designed while ago.
Discrete div 2 counter.asc


atmfjstc:
That sure is a lot of transistors you're gonna be using just for dividing the clock down to 1Hz. Think you're looking at 14 stages, that's 28 discrete transistors, diodes, and double the number of resistors. I wonder if there is a discrete component solution for dividing the clock in larger increments at a time (4, 8, 16 etc) with fewer components and acceptable precision. Maybe something like each pulse increasing the charge in a capacitor, and it could trigger a discharge and and output pulse when it accumulates the energy equivalent to, say, 8 input pulses?

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