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Suitable cable for hand controlled synth
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Ruebezahl



Joined: Mar 09, 2014
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PostPosted: Thu May 10, 2018 4:30 pm    Post subject: Suitable cable for hand controlled synth Reply with quote  Mark this post and the followings unread

Hello,

I am working on a hand-controlled synth right now. Its a simple CMOS-based square-wave-oscillator, where one oscillator is modulating the other. The chip is cd4093. The gimmick is that the synth is controlled by two gloves. One has a LDR (Light controlled resistor) inside and the other an on/off-Button, so i can controll the synth by my hands.

Now i have the problem that the on/off-Button doesn't really work. The on/off-Button is schematic-wise basically after all the sound-cicuit but just before the jack. Even when the button is not pressed i can hear the synth pretty clear, and when pressed its just a little louder. I figured its the fault of the cable. I used a shielded wire, where i used the core-wire to lead to the button in my hand and the shield to lead from the button to the jack. Probably not the wisest choice as apparently it leads to a lot of interference (Although the multimeter shows a very high resistance between shield and core) - But i would like to keep it at one cable leading to the button-glove if possible.
Any ideas what cable could work better? Maybe stereo cable where i put the shield to ground and use the two wires inside for the signal?
Or maybe do the on/off button as an actual on/off, just turn on/off the whole cicuit? That would mean quite some reassembling, but if its worth it...

Hope someone has some insight and can help me. Thanks a lot Smile

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Grumble



Joined: Nov 23, 2015
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PostPosted: Fri May 11, 2018 1:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Schematics would be very helpfull Cool
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stolenfat



Joined: Apr 17, 2008
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PostPosted: Fri May 11, 2018 1:43 am    Post subject: Reply with quote  Mark this post and the followings unread

you can rule the cable out if you use a multimeter to test connectivity: If you can determine the cable does pass voltage successfully from end to end then your problem lies else where... no?
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Blue Hell
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PostPosted: Fri May 11, 2018 2:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes a stereo cable would work much better .. provided that the cores are separately shielded. Ground the shield at the device ground.

But even then there may still be some bleed trough, which you might be able to reduce by adding a somewhat low valued resistor over the input of the final amplifier (say .. 1k).

The reason you get this bleed trough is not that there is a low resistance between the cable shield and core, but that the cable has capacity combined with the very high frequencies being present from square like signals.

The stereo cable version would make radio receivers in the neighborhood happier too.

And the reason for (maybe) still having some bleed trough is that square wave signals are pretty nasty. It is not that the fundamental tones go trough but their higher harmonics will, and then the ear will reconstruct the fundamental from the harmonics.

Alternatively, instead of switching the power, you could also use a relay to switch the audio on/off, and control that relay trough a long cable. In that case the cable type would not really matter.

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Ruebezahl



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PostPosted: Fri May 11, 2018 4:10 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks a lot for that insiht. I will go back and fourth between those options and see. Very Happy

I actually just did the method where i turn the circuit on/off instead of the audio on/off, because it was the only method where i wouldn't have to go buy new parts and - it works great!

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