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Sequencer ?
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e1999



Joined: Apr 25, 2019
Posts: 26
Location: naples

PostPosted: Wed Mar 18, 2020 3:38 pm    Post subject: Sequencer ? Reply with quote  Mark this post and the followings unread

Hi All,
I'm building a sequencer / touch programmer and was hoping for a little advice if possible.
attached is a rough schematic. I thought perhaps Phobos might be able to give some insight since the 4532 / 4051 combo is used in Quazar and is where I took the idea of pairing those two from. The sequencer is wired as shown in the schem. Two issues I'm having - 1) the 4051 bounces back to step 1 in between some of the steps, but not all of them, or sometimes all the leds flash faintly for a split second. I tried tying the inhibit pin to +V with a 10M resistor just to see if its hanging for a split second in between steps, but this made no difference. It bounces back more strongly on some steps and other steps not at all. 2) maybe related but the knobs' levels are affecting each other. Certain steps affect each other more than others.
Strange no? I double and triple checked all my connections, everything should be 100%. Also, has the same issues when using touch sensors, or clocking with the 4017 and touch sensors deactivated. Any ideas what might be causing this?


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PHOBoS



Joined: Jan 14, 2010
Posts: 4729
Location: Moon Base
Audio files: 642

PostPosted: Wed Mar 18, 2020 5:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Not sure if it's just some errors in the schematic or you left some things out but let's see:

- The reset pin of the 4017 doesn't need a pulldown resistor if it is directly connected to one of the outputs. It doesn't hurt though.
- CLK EN (pin 13) of the 4017 can be directly connected to GND.
- on Q1 (pin2 ) of the 4017 the resistor and output of the touchsensor are connected on the wrong side of the diode.
- the unused inputs of the 4532 should be connected but I am guessing you only drew 2 channels and you have more outputs of the 4017 + touch sensors connected to them.
- leave out the diodes connected between the 4051 and the pots.
- add current limiting resistors to the LEDs.
- add a pulldown resistor to your output jack, although there is probably a resistor on the input of whatever you connect it to. It would also be wise to buffer this output.

Do you only have 10V or is this derived from a bipolar 12V/15V supply ?

I only had a quick look but might have a better look at it this weekend.

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e1999



Joined: Apr 25, 2019
Posts: 26
Location: naples

PostPosted: Thu Mar 19, 2020 6:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Thank you Phobos!
I'm sorry, I drew out and uploaded that schematic late last night and yes there were some errors that do not reflect what I actually built:)

I am uploading a corrected version.

Yes I only drew 2 channels but there are in fact 8 on my project.

I put the pull down on the 4017 clock en and reset in case I want to add hold /reset buttons later.

Quote:

- leave out the diodes connected between the 4051 and the pots.


will do tonight... but I dont think this could be my problem?

Quote:

Do you only have 10V or is this derived from a bipolar 12V/15V supply ?


This is running 10v derived from 12v dc and a L7810.

The fact that step 1 blinks after other steps are touched and then released makes me think that maybe for a brief moment after a sensor is released, pin 6 inh of 4051 is still being held to ground by E0 of the 4532, since it is only when E0 sends out logic high that the 4051 will have no output. However its strange that it only does this for some of the steps.

As for the other issue of the pot positions affecting each other, do you think it could be because I daisy chained the grounds for the pots? It's odd because I never had this problem when I've made a sequencer taking the direct outputs of a 4017 into potentiometers.

Quote:

- add a pulldown resistor to your output jack, although there is probably a resistor on the input of whatever you connect it to. It would also be wise to buffer this output.


thanks for the tip will definitely do this. when you say buffer, do you mean inverting or could sending it through a non inverting buffer accomplish the same thing? (I drew into new schematic)

One other question...If I sent Q0 Q1 and Q2 of the 4532 into an inverter such as 40106 or 4049 would that enable the sequencer to play backwards?


Thanks again!


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PHOBoS



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PostPosted: Thu Mar 26, 2020 9:02 am    Post subject: Reply with quote  Mark this post and the followings unread

Daisy chaining the ground shouldn't be a problem, unless you use a very thin cable, since the current is low to begin with.
However it would be best to use a seperate cable for the LEDs. Also make sure the current through the LEDs is low since it will pull down the voltage,
using 10K resistors should work ok.

I don't think there is a need to use the Eout of the 4532 because one output of the 4017 will always be high and therefor the Eout should always be low
So I think you could just connect the INH pin of the 4051 directly to GND. I think there is anther chip that might be better to use here than the 4051,
let me see if I can find it. OK I think it is the CD4028 which isn't a mux but a decoder, no idea is it easy to get though. You could also try it without the
LEDs or use a seperate 4051 to drive those.

Non inverting buffer should work but power it by 12V otherwise you will probably not get a 10V output. Oh and you need a resistor to GND after the diodes
before the opamp but it might work ok with the LM358 as I believe it has some internal biasing.

Inverting the outputs of the 4532 wil indeed reverse the direction and if you use XOR gates you can toggle the direction.

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e1999



Joined: Apr 25, 2019
Posts: 26
Location: naples

PostPosted: Sun Mar 29, 2020 6:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Ok thanks:)

Wish that I could get this to work a bit more smoothly as the 4532 to 4051 combo opens up a lot of possibilities not present on a 4017 by itself....

I think the triggering back to the first step is something that has to do with maybe the inhibit but also the individual stages since it is only happening on 3 of the steps. I went back in and resoldered the connections for those steps but still no dice.

Thanks for the recommendation of the cd4028. I would like to try and get this working with 4051 because there are certain situations where I don't want it to output cv if no touch sensor is activated. But I'm sure that chip could be useful for something in the future:)
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