Using same 9V battery for two CMOS-based oscillator circuits, need to isolate them from each other

Thread Starter

mikeca

Joined Jul 22, 2019
5
Hi,

I'm pretty new to electronics and this is my first time posting here.

I'm looking for some help with a breadboard circuit I'm working on that uses two CMOS 4049 chips to create two oscillators that output via a mini-jack audio socket to a small portable speaker. The idea is two have the output from the chips mix together when they meet at the output, and have two spearate tones whose pitch I can control using potentiometers. Currently to do this I need to use separate 9v batteries for each circuit, as when I use the same power for both, the signals seem to blend into one.

So my question is: how can I use the same 9v battery to power these two CMOS chip circuits without their signals bleeding into each other?

I need something that isolates the power I think.

Here's a pic of a circuit similar to one of the two circuits I have (I don't have a camera here):



Thanks in advance for any help.

Mike
 

Audioguru

Joined Dec 20, 2007
11,249
Shorting oscillator outputs together poorly mixes their outputs together.
Use a resistor in series with each oscillator output (try 10k ohms) and where they are joined would be the input of another inverter from the CD4049. The output of the mixer CD4049 is the output that can weakly drive a speaker with a buzzing squarewave.
 

dl324

Joined Mar 30, 2015
11,458
Here's a pic of a circuit similar to one of the two circuits I have (I don't have a camera here):
That circuit can't be similar to yours. It has a 14 pin IC, CD4049 are 16 pin and don't have power pins on opposite corners.

A schematic, even hand drawn, is better than a picture of a breadboarded circuit; unless you you don't know how to use them, or trust you're ability to wire the circuit correctly.
 

Alec_t

Joined Sep 17, 2013
11,628
uses two CMOS 4049 chips to create two oscillators that output via a mini-jack audio socket to a small portable speaker.
That CMOS chip (or the CD40106, which is what the IC in your pic seems to be) can not work properly into the low impedance of a speaker. You need an amplifier to drive the speaker.
 

Thread Starter

mikeca

Joined Jul 22, 2019
5
That CMOS chip (or the CD40106, which is what the IC in your pic seems to be) can not work properly into the low impedance of a speaker. You need an amplifier to drive the speaker.
Oh it's a powered speaker and seems to work okay, thanks
 

Thread Starter

mikeca

Joined Jul 22, 2019
5
That circuit can't be similar to yours. It has a 14 pin IC, CD4049 are 16 pin and don't have power pins on opposite corners.

A schematic, even hand drawn, is better than a picture of a breadboarded circuit; unless you you don't know how to use them, or trust you're ability to wire the circuit correctly.
Yes I just wanted to give a rough idea of what I was doing really, but I accept this is probably insufficient information. I'll try and get a drawing together or find a camera. Thanks
 

Thread Starter

mikeca

Joined Jul 22, 2019
5
Shorting oscillator outputs together poorly mixes their outputs together.
Use a resistor in series with each oscillator output (try 10k ohms) and where they are joined would be the input of another inverter from the CD4049. The output of the mixer CD4049 is the output that can weakly drive a speaker with a buzzing squarewave.
Thanks very much for your response.

So I added the resistors in series to my two outputs from my 4049 chips and it worked pretty well in that I can now hear two distinct tones. However they still interfere with each other when I adjust their pitches using potentiometers. Is there some way to have them both use the same power source but isolate them from each other? Using diodes maybe?
 

MrChips

Joined Oct 2, 2009
21,818
It is very common to experience "pulling" or interference between two oscillators on the same board.
To overcome this, you need to pay attention to circuit design and board layout. You can try decoupling the power supplies as shown in the schematic below.

Power Supply Decoupling.JPG

R1/C1 and R2/C2 constitute two low-pass filters for your two separate power supply circuits.
C1 and C2 should be 10μF/16V tantalum electrolytic capacitors.

C3 and C4 are 0.1μF ceramic disc capacitors and must be placed as close as possible to the power and ground pins of the ICs using the shortest possible leads on the capacitors. These capacitors are not optional.

Finally, do not use the same IC for both oscillators. Use a separate IC for each oscillator.

Do not run the GND wire from one chip to the next (daisy chain). Treat the GND connection as a separate line back to each capacitor (C1 and C2) and back to the 9V battery as drawn in the schematic.
 

Thread Starter

mikeca

Joined Jul 22, 2019
5
It is very common to experience "pulling" or interference between two oscillators on the same board.
To overcome this, you need to pay attention to circuit design and board layout. You can try decoupling the power supplies as shown in the schematic below.

View attachment 182288

R1/C1 and R2/C2 constitute two low-pass filters for your two separate power supply circuits.
C1 and C2 should be 10μF/16V tantalum electrolytic capacitors.

C3 and C4 are 0.1μF ceramic disc capacitors and must be placed as close as possible to the power and ground pins of the ICs using the shortest possible leads on the capacitors. These capacitors are not optional.

Finally, do not use the same IC for both oscillators. Use a separate IC for each oscillator.

Do not run the GND wire from one chip to the next (daisy chain). Treat the GND connection as a separate line back to each capacitor (C1 and C2) and back to the 9V battery as drawn in the schematic.
Thanks so much for your time! This is exactly the kind of solution I was hoping to find. I'll try it out tonight.
 

dl324

Joined Mar 30, 2015
11,458
It is very common to experience "pulling" or interference between two oscillators on the same board.
I once tried to design a button cell sized circuit that utilized some "high" frequency oscillators using two SAW resonators on the same substrate. The idea was that the one near the edge would be more stable with changes in altitude and the frequency of the other would change. Unfortunately, I couldn't prevent the oscillators from interacting in my prototypes and the idea was shelved. Even a pager going off would pull my reference oscillator to the pager frequency (around 160MHz as I recall).
 

TeeKay6

Joined Apr 20, 2019
572
Yes I just wanted to give a rough idea of what I was doing really, but I accept this is probably insufficient information. I'll try and get a drawing together or find a camera. Thanks
@mikeca
Posting a schematic and any other info you have will help to narrow comments to those that are relevant to what you are actually trying to do. Otherwise, you will likely be inundated with info that is of little value to you.
 
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