Need a recommendation for a volume control knob please

Thread Starter

bradleyheathhays

Joined Sep 23, 2015
7
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!
 

AlbertHall

Joined Jun 4, 2014
10,246
If you simply want to reduce the volume then the simplest way would be to put tape or blu-tac across the hole in front of the speaker.
As it is piezo disc some experimentation would be needed to discover what resistance to include to control the volume.
 

wayneh

Joined Sep 9, 2010
16,399
I'd start with low ohms value pots, such as 100 ohms or less. If that doesn't reduce volume enough, move to 1000 ohms.

You'll need a pot rated to the power used by the speaker. I have only a guess that it may by in the 1-10W range. Pots for that power are not cheap so you may prefer to just keep trying different fixed resistors. Lightbulbs can be handy for testing purposes.
 

Thread Starter

bradleyheathhays

Joined Sep 23, 2015
7
Thanks for the advice guys. I have a better idea of what I'm looking at now. Couple questions though.

1- What type of resistors should I be looking at? Not sure how they're measured or what values I should be looking for.

and

2- How is it that a light bulb could be used for testing? Sounds interesting.
 

AlbertHall

Joined Jun 4, 2014
10,246
You'll need a pot rated to the power used by the speaker. I have only a guess that it may by in the 1-10W range. Pots for that power are not cheap so you may prefer to just keep trying different fixed resistors. Lightbulbs can be handy for testing purposes.
It is a piezo disc not a moving coil speaker.
 

AlbertHall

Joined Jun 4, 2014
10,246
I have the same thing as TS. I have finally succumbed and have taken it apart and viciously attacked it with a soldering iron.
Shown below, on the left, is the original circuit and, on the right, the addition of a 22k pot which works nicely as a volume control.
[EDIT] If trying this modification, I recommend unsoldering the speaker wires from the circuit board not from the piezo disc.
upload_2017-3-30_15-35-18.png
 

wayneh

Joined Sep 9, 2010
16,399
2- How is it that a light bulb could be used for testing? Sounds interesting.
A lightbulb is a fancy resistor, it can emit light in proportion to the current flowing through it, and its resistance increases with current (temperature, actually) which makes it somewhat self-protecting. It's relatively low ohms (making it not such a good choice after we see @AlbertHall 's info) and is built to handle power dissipation.
 
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