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 Forum index » DIY Hardware and Software » Lunettas - circuits inspired by Stanley Lunetta
Casper Electronics Sequencer
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CHRISKELLY



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PostPosted: Thu Apr 26, 2018 2:57 am    Post subject: Casper Electronics Sequencer Reply with quote  Mark this post and the followings unread

Found this schematic for an 8 step sequencer and was hoping someone could help me understand it better

http://electro-music.com/wiki/pmwiki.php?n=Schematics.StepSequencerByCasperElectronics

What is the reason for using transistors as LED drivers? Is it to save on power?

Also he sends the clock into a comparator - does this act like a note-length control or staccato?

Cheers
Chris
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Boerge



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PostPosted: Thu Apr 26, 2018 3:52 am    Post subject: Re: Casper Electronics Sequencer Reply with quote  Mark this post and the followings unread

CHRISKELLY wrote:
What is the reason for using transistors as LED drivers? Is it to save on power?


It reduces the load for the 4017 outputs.

CHRISKELLY wrote:
Also he sends the clock into a comparator - does this act like a note-length control or staccato?


Not likely. It may be omitted for clocking only with the internal 555 clock. But with external clock (note the switch and the input "ext. clock in") it is always a good idea to recover the pulses.

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Steveg



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PostPosted: Thu Apr 26, 2018 4:18 am    Post subject: Reply with quote  Mark this post and the followings unread

What Boerge said Smile
Each CMOS chip has a power rating on each output and an overall rating for the chip. Failing to keep to these ratings will reduce the life of the chip. For some people this is not a consideration. Many 40106 oscillator circuits have this problem. Usually the rating will work out to around 1ma (.001Amp) per output.

The comparator is probably overkill for external inputs and unnecessary for the 555 or 40106 oscillators. All it does is square up a possibly poorly shaped trigger into a nice sharp transition. A gradual transition can cause the chip to draw (and dissapate) a lot of excess power.
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CHRISKELLY



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PostPosted: Thu Apr 26, 2018 5:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the info chaps
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PHOBoS



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PostPosted: Thu Apr 26, 2018 7:20 am    Post subject: Reply with quote  Mark this post and the followings unread

with the comparator you can use a wider range of voltages and wave forms.
If you use a saw wave (or better inverse saw) you can actually set the gate length with it.

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CHRISKELLY



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PostPosted: Thu Apr 26, 2018 4:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks Phobos

How would that work with the 4017 though? Doesn't each step stay high until the ic transitions to the next step?

I've been trying to figure out a way to shorten the gate time from a 4017. It kind of worked by sending the clock and 4017 output into an AND gate, so that the output was only high for half of the (squarewave) clock cycle.
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PHOBoS



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PostPosted: Thu Apr 26, 2018 5:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

CHRISKELLY wrote:
I've been trying to figure out a way to shorten the gate time from a 4017. It kind of worked by sending the clock and 4017 output into an AND gate, so that the output was only high for half of the (squarewave) clock cycle.

That's how you do it and how it's done in the schematic so If you change the duty cycle of the clock signal you directly
change the on time of the outputs. If you use an inverted saw wave in combination with the comparator you can easily
adjust the duty cycle (and could control it with an external control voltage as well). Of course it is not so common to clock
things with a saw wave. You can change the duty cylcle of a squarewave but it will be frequency dependent. Unless you go
for a digital approach where you use a faster clock and change the dutycycle in steps.

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