Hi all, Another digital question. I'm doing this pulse thing. Pulse widths were,
1,2,4,8,16.. simple set by a rotary switch pulling one bit high.The boss wanted a finer division, which I first thought would take AND gates, but then I thought about just diodes to only pull high those lines I want. (Rather than explain more here's a circuit fragment.)
So this gives me
2,3,4,6,8,12,16,24......This seems to work just fine... is there some gotcha I'm missing?
TIA
George H.
On Friday, February 26, 2016 at 7:47:53 AM UTC-8, George Herold wrote: .
Should work OK. The shown values will work with CMOS if you don't try to operate below 3V power (you lose some logic margin by diode drops).
The select circuit is now more complex to wire, and harder to understand, than a three digit thumbwheel switch...
Grin.... (thanks whit3rd.)
George H.
Am I missing something, or does the RCO output on IC14 give you the end-of-time output you want? What's with the NAND gates?
Check to see that you have enough margin. Margin can be improved by using schottkey diodes and/or 74HTC161 counters.
Check where pins 8 and 9 of U$8 are going.
-- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Oh, this is just a fragment, I can post the whole thing on Monday, and you can rip it apart. I set a bit and then down count... all the RCO's go to an RS and then into a D-flip which shuts things down on the next clock cycle. (My digital design is a bit "organic". I made something that mostly worked and then cleaned up the bit's that didn't... There is most likely some better way to do it.)
George H.
Cmos and 5V supply. The pins look ok... I did all the odd numbers first they go straight. Anyway I don't think we need finer divisions in time. (That's my bosses idea.) The whole circuit sends a current pulse to a resistor* and measures the voltage. (to determine the energy delivered.) I've got two knobs, one for T and one for I... I(current) should have the finer divisions.
I did the analog part ~1 year ago, but now I need to pick the current sense resistors. I did a series string today, but I don't like it.. too much heat, so I'll try parallel. For what ever reason it's harder for me to think about parallel, conductance rather than resistance.
George H.
*at the cost of another wire a FET would be better.
Look closer. You've got a wire going from pin 8 and a diode going to that same wire from pin 9. So if pin 9 is high and 8 low, you'll have an effective short.
-- www.wescottdesign.com
Hi Tim, OK I starred at it three times now. (It still looks OK to me... but if I spin it this way and it's wrong I'll be sure to shout out to you.)
The U$8 is the rotary switch.. (Yeah I just made the model for it and I should have given it a better designator... lazy on my part.) The switch is BBM, so there should not be any shorts.
George H.
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