# Reducing frequency in the 20Hz-20KHz range for ring oscillator

#### IbrahimF

Joined Jul 21, 2017
25
Hello

Basically I am trying to build a circuit to output some noise through a loudspeaker.
attachedis the circuit simulation using multisim

The frequency is in 122KHz which is to high to be heard is there anyway I can reduce it to about 10Khz. or make something to make the frequency adusjtable.

Thanks

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#### wayneh

Joined Sep 9, 2010
17,153
Basically I am trying to build a circuit to output some noise through a loudspeaker.
I haven't looked at your sim at all but I'm wondering what sort of output you want. It obviously won't resemble the original waveform unless you store it and slow it down for replay. I've seen bat (flying rodent) detectors that work this way.

If you just have a tone, my approach would be to run it through a comparator to square the peaks, then feed that to a divide-by-16 IC. The output would then be a square wave with a frequency directly proportional to the original.

#### IbrahimF

Joined Jul 21, 2017
25
I haven't looked at your sim at all but I'm wondering what sort of output you want. It obviously won't resemble the original waveform unless you store it and slow it down for replay. I've seen bat (flying rodent) detectors that work this way.

If you just have a tone, my approach would be to run it through a comparator to square the peaks, then feed that to a divide-by-16 IC. The output would then be a square wave with a frequency directly proportional to the original.

I am basically using TTL inverters to produce the oscillation. the output waves are triangle waves, and yes I just have a tone and I would like to listen to frequencies between 20Hz and 20KHz is there any way to make the frequency adjustable?

#### Audioguru

Joined Dec 20, 2007
11,249
Do you like to hear the "buzzing" sound of as triangle waveform? Why not make a sinewave audio Wien Bridge oscillator instead?

#### IbrahimF

Joined Jul 21, 2017
25
Thanks for the suggestion.

Is there a way to make the frequency adjustable?

#### Audioguru

Joined Dec 20, 2007
11,249
All RC oscillators have an adjustable frequency. But your extremely simple ring oscillator has no R or C to adjust.

#### IbrahimF

Joined Jul 21, 2017
25
All RC oscillators have an adjustable frequency. But your extremely simple ring oscillator has no R or C to adjust.

Would adding a RC in the feedback element work. The input signal is 5V DC power supply. Which i add and then remove

#### Audioguru

Joined Dec 20, 2007
11,249
The extremely simple ring oscillator you built is a very Mickey Mouse oscillator because its frequency will be different with each IC it uses. You should make a better oscillator that has resistors and capacitors that determine the frequency.

#### IbrahimF

Joined Jul 21, 2017
25

The project tasks requires TTL inverters to build the oscillator. I can add as many transistors I need

#### Audioguru

Joined Dec 20, 2007
11,249

The project tasks requires TTL inverters to build the oscillator. I can add as many transistors I need
I used old fashioned TTL about 50 years ago. Since then I use more modern Cmos logic where an RC oscillator works well and can have an adjustable frequency.

Use a logic counter IC to divide the ring oscillator frequency down then abruptly change the frequency in octaves with a switch.

#### DickCappels

Joined Aug 21, 2008
7,547
If you make one or more resistors into post you can adjust the frequency. Also, adding capacitors from the drains to ground will lower the frequency.

#### IbrahimF

Joined Jul 21, 2017
25
If you make one or more resistors into post you can adjust the frequency. Also, adding capacitors from the drains to ground will lower the frequency.

It worked. but why does changing the resistors change frequency, also I noticed on increasing the power supply the frequency increases

Thanks

#### DickCappels

Joined Aug 21, 2008
7,547
You have lowered the frequency considerable.

Wow... that was not what I wanted to say.

If you make one or more collector resistors variable you can vary the frequency.

#### IbrahimF

Joined Jul 21, 2017
25
does that behave like a RC circuit?

#### Audioguru

Joined Dec 20, 2007
11,249
Why do you say you must use an old TTL inverter IC then show a completely different circuit with Mosfets and resistors in the simulation?? 50 years ago I never tried a capacitor to ground on the output of a 7404 inverter to see if it blows up or not.