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 Forum index » DIY Hardware and Software » Circuit Bending
cd40106 jumping in tones
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samsam



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PostPosted: Sat Mar 04, 2017 11:53 am    Post subject: cd40106 jumping in tones Reply with quote  Mark this post and the followings unread

Hi everyone.

I'm building something that should be really easy.

I have two oscillators made out of a cd40106 chip. Problem is that the sweep is not smooth between notes when i turn my 100k potentiometer. I have tried many different capacitor but the result still the same. My oscillator is jumping from note to note.

Do you have any idea of what may be causing this ?
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JovianPyx



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PostPosted: Sat Mar 04, 2017 12:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

If the 100K pot isn't new, there could be worn spots on the resistive element which will definitely cause this exact symptom.

Ever turn a volume knob on an old amp and have the sound crackle or jump? Same issue.

I can't think of anything else other than that. Even if the pot is brand new, I'd try another new one.

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Blue Hell
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PostPosted: Sat Mar 04, 2017 12:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

two oscillators on one chip? if so - they may sync to each other. could try to decouple the power supply (capacitor over it close to the chip).
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JovianPyx



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PostPosted: Sat Mar 04, 2017 1:04 pm    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
two oscillators on one chip? if so - they may sync to each other. could try to decouple the power supply (capacitor over it close to the chip).


Oh yes, that's possible too. However, bypassing may not completely eliminate the problem because the gates are tied together internally which means that each oscillator cannot be separately bypassed. A better way is to use 2 chips, one for each oscillator, power each chip through an LED from V+ to the Vdd pin and a cap (like 100uF) from Vdd to ground. That is the way it's done in the PAiA Fatman and it works very well. Do not expect the LED to light, the 40106 won't draw enough current for that, however, the LED will work as a light weight diode regardless of whether it lights or not. A small signal diode such as 1N4148 will not work (at least it's never worked for me).

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samsam



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PostPosted: Sat Mar 04, 2017 2:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the replies.

I have tried with one oscillator only and it does the same thing. Same problem when i change the pot, it jumps from note to note.

I have changed the 5 volt power supply for a 9 volt and it seems to work ok know.

Does this chip doesn't work on 5 volt ?
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PHOBoS



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PostPosted: Sat Mar 04, 2017 3:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

it should work fine on 5V.
Did you connect all the unused inputs to GND or V+ ? Floating inputs can cause
some weird behaviour sometimes even if the gates themselves aren't used.

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JovianPyx



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PostPosted: Sat Mar 04, 2017 8:34 pm    Post subject: Reply with quote  Mark this post and the followings unread

What PHOBoS said...

and

Can you show us the *exact* schematic?

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samsam



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PostPosted: Sun Mar 05, 2017 7:19 am    Post subject: Reply with quote  Mark this post and the followings unread

I didn't know all the other inputs of the chips had to be connected as well.
Should they be connected to ground ?

the schematic is really the most basic way to make oscillators out of a cd40106.

Pin 14 to ground
Pin 7 to 5 or 9 volt

Pin 1 with a capacitor to ground
A 100k potentiometer connected between pin 1 and 2.
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JovianPyx



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PostPosted: Sun Mar 05, 2017 8:23 am    Post subject: Reply with quote  Mark this post and the followings unread

In all cases of CMOS logic devices, unused inputs must be grounded (Vss) or tied to Vdd. Unused outputs should be left open.

Given that we're talking about an unused logic gate, it makes no difference whether the inputs are tied high or low. Do as is convenient for the layout. Just never leave them open.

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