Hi all, I mentioned this digital question on SED. (It's really not much of a hair ball...) The goal is to make precision* pulses from 1/16th to 32 seconds. (the numbers may change) In a factor of 2 progression, 1,2,4,8... I made the following about a year ago.
So at the moment the clk is coming from a function generator. The current plan is to use a 32.79?kHz oscillator and divide it down.
Q1, Is there any advantage to using a higher freq. crystal? (say dividing down 10 MHz.)
Q2, Is there some better way? I started with the 74hc191 and worked backwards.
Given a 32kHz clk, I need two divide by 2^10 stages, I'm not sure how to do the variable divider, I tried loading different bits into the '191 and then down counting. (the schematic doesn't show that I'm currently up counting.) But I got divide by N-1 rather than N... so more thought (or more digital logic) is needed.
And finally a minor question. I made these one shots out of 74hc14, a cap, resistor and Schottky diode. I added some 1 k ohm resistors in series with the cap, R1 and R2, Is there any reason to have 'em?
Thanks, Sorry for the rather long post.
George H.
*The needed precision is not all that great, timewise. 100 ppm, should not be too hard to do better than that.