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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
trigger times on a 16 step sequencer?
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elmegil



Joined: Mar 20, 2012
Posts: 2112
Location: Chicago
Audio files: 16

PostPosted: Wed Feb 20, 2019 10:43 pm    Post subject: trigger times on a 16 step sequencer? Reply with quote  Mark this post and the followings unread

Building a 16 step rotary analog sequencer....

Using bananas instead of jacks. Have a ground connection for interfacing between banana boxes or to other things with a Format Jumbler.

Everything seems reasonably OK except the trigger time is RIDICULOUSLY fast.

Like 100usec. Looking at the schematic, the gate signal goes through a 1nF cap and has a 100K pull up, and that feeds a schmitt trigger inverter. 1nF * 100K has a time constant of 1ms, so I'm guessing that I should be seeing 1ms triggers rather than 100usec.

Double checked the (printed) values of the cap and the resistor, they appear to be correct.

I know in-circuit measurements are typically inaccurate, but measuring R28 shows 100.something Kohms, and C13 shows 1.55nF. So if anything it should be longer than 1ms.

Any ideas? Does someone have one of their own they could measure the trigger time on and be sure I'm not crazy?

(BTW I'm using 12V MFOS wall wart for power, in a standalone box)

Thanks!
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Grumble



Joined: Nov 23, 2015
Posts: 1040
Location: Netherlands
Audio files: 29

PostPosted: Thu Feb 21, 2019 12:01 am    Post subject: Reply with quote  Mark this post and the followings unread

http://sim.okawa-denshi.jp/en/CRhikeisan.htm

t[s],f(t)
0,1
8.0E-6,0.92311634638664
1.6E-5,0.85214378896621
2.4E-5,0.78662786106655
3.2E-5,0.72614903707369
4.0E-5,0.67032004603564
4.8E-5,0.61878339180614
5.6E-5,0.57120906384881
6.4E-5,0.52729242404305
7.2E-5,0.48675225595997
8.0E-5,0.44932896411722
8.8E-5,0.41478291168158
9.6E-5,0.38289288597511

by using the step response data you can now calculate the pulsewidth of your pulse. The pulsewidth also depends on what comes next, a ‘regular’ gate or a schmittrigger?

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elmegil



Joined: Mar 20, 2012
Posts: 2112
Location: Chicago
Audio files: 16

PostPosted: Thu Feb 21, 2019 7:51 am    Post subject: Reply with quote  Mark this post and the followings unread

1) next is an inverting schmitt trigger as stated. Specifically 40106.

2) My math is bad. 1E5 * 1E-9 = 100usec, not 1ms. So it's behaving as it should.

3) however, since a 100usec / .1 ms pulse is way thinner than most things deal with, I have added a 10nF in parallel with the filter cap and now have roughly 1ms pulse as I would want/expect.
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