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Need Help Finding Clock Oscillator for Sequencer
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NuttyMonk



Joined: Jun 30, 2020
Posts: 30
Location: UK

PostPosted: Thu Sep 17, 2020 1:23 pm    Post subject: Need Help Finding Clock Oscillator for Sequencer Reply with quote  Mark this post and the followings unread

Hi all,

i've been working on a sequencer for a wee while now. I've got a lot of it sorted out but i keep coming back to the clock signal itself. I'm currently running an Arduino Nano with some code of my own to create the clock signal which is also able to be CV controlled so each of the 16 steps can have it's own length to create fully modifiable and complex rhythms (got the idea from a Colin Benders video on Youtube). Although it seems to work ok i'm just not happy with it.

What i really want is a really simple square wave oscillator that works in the BPM ranges (say 10bpm - 500bpm which is 0.17Hz - 8.33Hz). It has to be simple, fully temperature compensated with no extra features such as Exp/Linear FM, Hard/Soft Sync, Pulse Width or PWM. It should also be possible to apply CV modulation to it so that i can alter the tempo for each step with the 16 Step Mod pots i intend to use.

I tried looking at taking a Thomas Henry design and removing the extraneous functions from it but his designs always include FM and Sync and i'm not sure how to remove them and keep it working correctly. The one thing i like about the TH designs is the way that the frequency adjustments are summed in an opamp before being applied to the oscillator. This kind of setup would make it easier for me to implement my ideas and understand what is going on with CV control.

Can anyone offer any advice on a decent Clock Oscillator design that i can use for this? Low component count and simplicity are the aim along with the CV mod functionality. Simple square wave output with no other waveforms. No FM modulation, Sync or PWM. Pulse Width could be part of it since it doesn't matter too much.

Thanks in advance for any help peeps can give.

Cheers

NM
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Clack



Joined: Aug 08, 2005
Posts: 438
Location: Walthamstow - london
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PostPosted: Sat Sep 19, 2020 10:40 am    Post subject: Reply with quote  Mark this post and the followings unread

Post the TH oscillator you had in mind and we could see what you can remove to strip it down and how to bring the frequency down.

Do you want the CV control to be 1v/oct? if not the temp correction is not needed.

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NuttyMonk



Joined: Jun 30, 2020
Posts: 30
Location: UK

PostPosted: Sat Sep 19, 2020 11:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi Clack, thanks for replying.

The TH VCO555 is a nice oscillator but there is so much which is interconnected and the square wave is so far away from the inputs and 555 timer IC that i decided to look at using an AS3340 instead. That is working quite well now. I have it doing BPM-rate frequencies with a pretty clean waveform and a Coarse and Fine knob. Also the CV is easy to implement on it. The only other IC i need is a TL072 to buffer the PW voltage (don't really know if i need that buffer) and to control the gain/DC offset of the square waveform output. No transistors needed at all and just a Poly cap for the frequency range. Tuning shouldn't be hard too since i'm not looking at using v/Oct on it.

The problem i have now is trying to get my arduino BPM counter working right. I'm getting lots of interference on the pins so it registers HIGH easily enough but when it's meant to register LOW on a pin it wobbles between HIGH and LOW making it completely unusable.

Thanks for your offer of help though Clack.

Cheers

NM

[EDIT] fixed the Arduino problem. I hadn't connected the ground pin for the ground reference, lol.
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