I want to add a volume control to my project where I have a piezo on a 1K resistor, drawing 5mA at 5v.
This is the pizeo I'm using:
For my first attempt, I added a 10K linear potentiometer in series with the resistor, and connected to act as a variable resistor. But when I turn the knob all the way down, my piezo gets significantly quieter... but it's still quite audible.
Now obviously the problem here is my pot isn't big enough; but I don't know how big a pot I should use. I need a pot which is big enough that I can't hear the piezo when I have it turned all the way down, but small enough that it's not compeltely silent over half the knob's travel.
I tried calculating what size pot I'd need based on sound pressure levels and assuming that halving the current would halve the sound pressure, but I got nonsensical results like having to reduce the current by 5000x to get near silence, which would require a 5 million ohm pot.
So, any suggestions for what size pot I should go with? I intend to use an audio pot btw, I just used a linear one because that's what I had at hand.
Why don't you first try using your existing pot as a voltage divider and see if it controls the piezo better. Wire the fixed terminals of the pot to the Arduino output pin and ground, and the wiper terminal to the piezo and ground the other side of the piezo.
Huh. That works great! And it looks like I won't have to change my PCB layout too much to make those connections either. Thanks!
I left my 1K resistor on the pin and connected the center pin of the pot to that btw. I assume when the wiper is all the way at +5v that I still need to limit the current.
If I connect an audio pot up to this, is it gonna matter which one of the outer pins I connect to ground and which I connect to the pin on the Arduino? Or is using an audio pot with this setup not a good idea? I'm concerned about how cheap audio pots have tow discreete regions of resistance on them and whether flipping things around might produce weird volume curves.
The linear pot varies the volume okay, though most of the loudness is on the top end.
how cheap audio pots have tow discreete regions of resistance on them
No they don't they have a log law which can seem like two regions but it is continuous. Normally they are such that when the pot is turned fully anti clockwise the wiper will be at the ground end.
All this tapering proved a rather expensive exercise, so manufacturers economised ("they" won't notice the difference!), and worked out a method of using two resistance elements of differing resistivity, and joining them to create what I referred to as the "Commercial log" taper. In short, it doesn't work (not properly, anyway), and the discontinuity where the two sections join is almost always audible with cheap "log" pots.
Normally they are such that when the pot is turned fully anti clockwise the wiper will be at the ground end.
Hm... Makes sense.
Unfortunately my volume control will be on the left side of my prop. That means turning it clockwise to increase the volume would have the user turning the knob towards them. Bit counterintuitive. Guess I gotta decide if it's more important to have an audio taper or have the volume increase as you turn the knob towards the front of the prop.
(And yeah, I know it's possible to alter the law of a pot so I could make a custom one, but it's not worh the extra complexity.)
I'm not saying you're wrong, as I really have no clue how pots are made, but this page, which is what I was quoting, seems to disagree with you:
You're probably talking about what he is terming "commercial log" taper pots - I've never seen one; but I suppose they could exist. Stay away from them unless you need such a taper (I suppose there could be a use for such a strange taper).
Typically, though, you see logarithmic tapers and linear tapers (I've never seen an anti-log taper, either - but I suppose it could exist, too). Which one you use will depend on the application and how you want things to respond.
That means turning it clockwise to increase the volume would have the user turning the knob towards them. Bit counterintuitive.
I would say it would only "feel wrong", and probably from a right-hander's perspective at that; do left handers feel that knobs on their right side rotating clockwise for "increase" feel similar?
I have never seen a volume control operate "backwards" like you mention; probably the best thing would be to build a prototype and test it out on the people who would use it; they will tell you in a hurry whether they like it or not.
Grumpy_Mike, maybe I'm more naïve than you, but even I get suspicious when a site diss'es some audio components, and also sells its own audiophile kits.
But then I can't hear the difference between copper cables and oxygen-free copper cables
Last week my team and I was repairing my managers super custom built amplifier from the late 80s. We had to replace one capacitor with a ceramic, because it was all we had on hand. He was concerned that he would here the difference between the two channels. So we said "you tell us what channel it is in and we will change it". He can't.
I always found it odd that by the time you were rich enough to afford a decent amplifier and speaker set up, your ears were so shot you couldn't tell.
Guess I gotta decide if it's more important to have an audio taper or have the volume increase as you turn the knob towards the front of the prop.
