"mapping voltage" on an analog potentiometer using a voltage divider

Question

I'm working on a simple project to learn electrical circuits. I built a little sound box that will play tones when you press buttons.

The battery provides 3volts and the "power boost" is a buck converter that increases the voltage to the 9v needed to power the speaker.

I wanted to include a potentiometer to adjust the volume so I used one I had on hand. The problem was that most of the range of the potentiometer provided so little voltage that no sound came out of the speaker and then right as you get towards the end the volume shoots up.

I read a bit online and it seemed like using an analog potentiometer would resolve the issue since the resistance changed exponentially instead of linearly.

I swapped out the potentiometers, but it seems like I'm running into the same problem: most of the range of the potentiometer's resistance the voltage is so low that no sound comes out of the speaker.

I was talking with a friend and mentioned the issue and he suggested using a voltage divider to map the desired voltage range along the potentiometer. This sounds sensible, but I have no idea how it should be implemented.

Does using a voltage divider to map the voltage range to the speaker make sense? If so, how would I do it? I've been searching around for things like "potentiometer with a voltage divider" and "mapping voltage on a potentiometer" and have found plenty of results, but not for the task I'm trying to accomplish.

Any suggestions? Helpful links?

Answer 1

It appears that you are using the potentiometer incorrectly for two reasons:

1. You are using it as a variable resistor instead of a potentiometer.
2. You have it on the speaker line. You should have it before the amplifier.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. (a) Rheostat. (b) Potentiometer. (c) Volume control.

Your diagram doesn't show the resistance value of the potentiometer or the speaker but let's say they are 1k and 8 Ω. 1k is a huge resistance to put in front of an 8 Ω speaker and only a small fraction of the power will get to the speaker. It's only when you decrease it to < 100 Ω that you can probably hear any change.

For a volume control we use a potentiometer. Note in Figure 1b that this has the bottom terminal connected to circuit ground. That means that as we slide the wiper up from the bottom the output voltage will vary from 0% to 100% of whatever is coming in on the IN terminal. (The output will actually be somewhat less if you have a load connected to the wiper. It will be very much less if you tried to connect your 8 Ω speaker to the wiper.)

What you need to do is get a proper amplifier circuit and hook it up as shown in (c). This way the volume control only has to deal with low powered signals and the amplifier boosts these to drive the speaker directly. That's how all amplification systems do it.

You need to draw proper schematics (component symbols, part numbers, designations - R1, R2, etc.) to help you and others understand your circuit. There are many online free tools and there is a CircuitLab button on the editor toolbar on this site (that I used for Figure 1). Have fun.

Answer 2

A volume control is generally wired as a voltage divider, like so:

^{simulate this circuit – Schematic created using CircuitLab}

It is hard to say how this should be done in your situation, without a proper schematic of the audio portion of the circuit.