• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Need a recommendation for a volume control knob please

Status
Not open for further replies.
Complete novice here, and I'm trying to figure out what little volume control knob I need to splice into this wire here...



...in order to control the volume of the speaker on this 2 C cell powered alarm device. This is part of a 2 unit warning system where one box is the motion sensor, and the one pictured is the remote alarm. When viewed from the outside of the box (through the protective vents), the speaker appears to be made of copper foil.

I have no clue what to look for even if the part was described to me, so would someone please be kind enough to provide a link for a small volume control knob I could splice in that would be appropriate for this application. Ideally I'd like to drill a small hole and mount it so the knob protrudes through to the outside of the plastic box.

Thanks!
 

alec_t

Well-Known Member
Most Helpful Member
The speaker looks like a standard piezo disc type of sounder. If it is driven by a fixed frequency oscillator then a series rheostat might be a usable volume control. However, if the sounder is the frequency-determining part of a self-resonant oscillator circuit then a series rheostat may simply prevent any oscillation. You could try various fixed resistors first, to see what effect they have. If that works then you will have a basis for choosing a potentiometer (rheostat).
 

JonSea

Well-Known Member
Most Helpful Member
If it's a piezo beeper, you won't be able to change the volume much. Restricting the opening to the outside will probably be fthe best bet.
 

dr pepper

Well-Known Member
Most Helpful Member
As above a piece of tape over the hole, very effective.
 
Sorry so late getting back here...too many irons in the fire lately.

But thanks for the advice. That sounds like exactly what I needed to hear. I'll prob get a 10k and 1k pot and see what happens with them.

Alec would you mind directing me to or describing what type of fixed resistors I need to consider? I know what they look like and that they're color coded with stripes on the side but as far as knowing how they're measured I'm in the dark.
 
Last edited:

JonSea

Well-Known Member
Most Helpful Member
You seem to have read a different set of replies than I see here. Not too long ago, I thought changing the volume on a piezo beeper would be a piece of cake. I was mistaken, and in the end, replaced a piezo beeper with a subminiture speaker and a 6 IC circuit to have controllable volume and frequency.

Well into my quest to control volume on a piezo beeper, I came across the following few paragraphs in the middle of a product data sheet. Yes, you can control piezo beeper volume, over an extremely tiny range if you don't care what the beep sounds like.

Have you ever wondered why you can't find a piezo beeper with a volume control? Because you can't change the volume enough to matter.
tmp_8231-SmartSelectImage_2017-03-29-20-54-101141368958.png
 
You're right Jon I actually sent my question to another electronics type forum. Unfortunately it seems like in the end I might not be able to adjust the volume much at all. Is there any chance I could just clip the two wires entirely and install my own speaker and volume control? If so what kind of speaker would that be. I assume it would be controlled with the same type of potentiometer we've been talking about.
 

JonSea

Well-Known Member
Most Helpful Member
Nope. The thing is designed to drive a piezo element which is totally different than an 8 ohm speaker.

Sorry, but there's not an easy solution to your issue other than mechanically blocking the output path.
 

alec_t

Well-Known Member
Most Helpful Member
Alec would you mind directing me to or describing what type of fixed resistors I need to consider? I know what they look like and that they're color coded with stripes on the side but as far as knowing how they're measured I'm in the dark.
If you want to try fixed resistors, googling "resistor colour codes" will find some charts to guide you as to the colour bands for specific values. 1/4 Watt 10kΩ/1kΩ types might suit. However, you may find it almost as cheap (depending on your component source, minimum order quantities and shipping charges) just to buy a 10k pot as you suggested.
 

JonSea

Well-Known Member
Most Helpful Member
I wonder if alec_t has ever actually tried this idea, or merely thinks it should be easy? It's easy enough to try a pot in series with the piezo element, but I would be astonished if it works.

This photo shows my solution to controlling piezo beeper pitch and volume. A controllable oscillator chip feeds a square wave to an integrater stage that converts the square wave to a triangle wave for a more pleasant tone. A digital pot controls the level of the signal to an amp chip that drives a speaker. I wasn't able to find any approach to changing volume on a piezo beeper in a meaningfull way otherwise and believe me, I looked for easier ways!
tmp_23308-SmartSelectImage_2017-03-30-03-23-051373563087.png
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I wasn't able to find any approach to changing volume on a piezo beeper in a meaningfull way otherwise and believe me, I looked for easier ways!
Isn't the device in question a piezo 'speaker', rather than a 'beeper' - in which case a simple pot wired as a potentiometer is all that's required (simply in-series isn't going to work very well). The value of course depends on the impedance of the source, and of the piezo speaker.
 

JonSea

Well-Known Member
Most Helpful Member
True, the device shown is a piezo element. These elements look like an entirely capacitive high impedence load to the driver circuit. I don't believe installing a pot in the circuit makes sense.

It might work. It might introduce some distortions that you can convince yourself are a change in volume. In my research in controlling volume of piezo transducers, I didn't see any reference to this technique. Yes, my starting point was an active beeper, but my solution could have been a piezo element, had I found a simple way to control volume - I did not. The only methods I found to control volume on a piezo element is to control the duty cycle of the driving square wave, which resulted in a modest volume change. I did quite a bit of research on this, and nowhere was a pot used to control volume of a piezo element.

Perhaps I am a crappy researcher and perhaps I know nothing above piezo transducers (only having used them for 30 years or so doing vibration analysis). My concerns here are somebody who thinks this is a piece of cake (but has never done this) who presents it as a fact to someone who has little knowledge of the subject.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
True, the device shown is a piezo element. These elements look like an entirely capacitive high impedence load to the driver circuit. I don't believe installing a pot in the circuit makes sense.

It might work. It might introduce some distortions that you can convince yourself are a change in volume. In my research in controlling volume of piezo transducers, I didn't see any reference to this technique. Yes, my starting point was an active beeper, but my solution could have been a piezo element, had I found a simple way to control volume - I did not. The only methods I found to control volume on a piezo element is to control the duty cycle of the driving square wave, which resulted in a modest volume change. I did quite a bit of research on this, and nowhere was a pot used to control volume of a piezo element.

Perhaps I am a crappy researcher and perhaps I know nothing above piezo transducers (only having used them for 30 years or so doing vibration analysis). My concerns here are somebody who thinks this is a piece of cake (but has never done this) who presents it as a fact to someone who has little knowledge of the subject.
Sorry, but you're making a big fuss over absolutely nothing, the volume from a piezo speaker is completely dependent on the voltage applied to it (exactly as a normal speaker), lowering the voltage lowers the volume exactly as normal.

The reason you're confused is that you were using an active beeper, where the electronics are built-in - thus you have no control over anything, other than the power supply feeding it.

It's a simple enough process, a piezo speaker (or any piezo element) bends in direct relation to the voltage applied to it, applying an AC voltage makes it bend back and forth, this produces audio. The higher the voltage the more it bends, and the higher the volume - apply too much and it cracks and is destroyed.

Have you never seen a crystal earpiece?, that's just a smaller piezo disk in a convenient plastic moulding - plug it in your radio and the volume control of the radio adjusts the volume in the earpiece perfectly.

Incidentally - a number of years ago now the UK magazine EPE published a freezer alarm using a PIC 12C508, a thermistor, and a piezo sounder. I had the capability of programming the OTP 12C508 series, so I built one as a matter of interest. I found the alarm wasn't really loud enough from 5 volts, so I modified the code and circuit (simply wiring the piezo across two I/O pins) to drive the piezo in bridge mode, This greatly increased the volume, as volume from a piezo is proportional to drive voltage, and my changes were published in the letters page of the magazine.
 
Status
Not open for further replies.

EE World Online Articles

Loading
Top