On car and home HiFi I have a knob to control the volume. It is not a variable resistor - it turns infinately. I guess is somehow creates a proportional and directional signal to the amplifier - but what is in the mechanism and how does it work?
An incremental rotary encoder and either digital control of the amp gain, or software scales the volume accordingly while amp runs at fixed gain.
on 30/11/2016, DerbyBorn supposed :
They now use an opto-coupler, basically they (two pairs, so they get a direction) shine a beam of light through a segmented disk. The output of which controls an IC to vary the volume. They are used on many things - volume controls, tuning controls, microwave ovens and etc.. Anything which needs a rotary control to change a value.
Not unlike a stepper motor but with the coils connected to a sensor that determines direction and rate of rotation from the clicks.
Prior to that there were absolute position encoders using Grey codes that would allow you to read the angle (but costly to do at high precision). Telescope drives and CNC tools use them for feedback.
When I built one back in the 70's the cheapest was a light source, a 50
50 slotted wheel., and two photo detectors, plus a bit of CMOS logicCoils and magnets are a no no as they don't detect *very slow* movement.
Not all. Before optical some used multiple sliding contacts, and become annoyingly noisy. I had a mini system and even a Sony walkman with issues like this where at a random point the contacts would become open circuit and assist in digitally creating a gain setting not too distant from the number 11.
Then you have tinnitus, lost teeth and sore joints for a few hours after the unscheduled urgent launch to explore the galaxy far far away beyond the ceiling in your room....
Some use hall effect sensors too. I'd say that easier than messing about with light beams.
A cheap and popular method is still used by mice, well not lots of mouses b ut optical mice still use an LED. They don't use a light chopper but 'take' a picture of teh surface table and use that and subsequent movments to wor k out it;s position. I;'m not sure if hall effect sensors are still used fo r this sort of thin unless in a specialsed area of use.
In a binary fashion.
IMHO it has only two settings - too quiet or too loud...
I'd guess you'd need a much finer resolution with a mouse, though.
My DAB radio does a full rotation in 20 clicks but volume goes from 0 to
32 so needs more than a full rotation, my car radio is probably similar.
Seems quite possible nowadays as tha's how the majoroty of mice costing mor e than £10 work. I belive you can stil buy mice with a trackball and a chopper circuit if you really want to.
Some are optical, some are just pulse generators. I think its a way to stop that nasty issue of crackling as they wear and get damp as often is the way in cars. Most simply then are driving the logic on one part of the control chip. How it works is rather academic as often you need the actual proper part these days. I personally do not like them as as a blind person nowadays, there seems in most cases to be no way to actually calibrate the knob as anywhere is anywhere as on switch on it might be as it was last time or set to some arbitrary point for the system. My first encounter with this was on a minidisc recorder. Not only did it have continuous clicks, but if you move it a short distance fast, it actually incremented faster than the normal amount, so some kind of speed of movement was programmed in just to add more confusion. add to that a mode where it looked at the digitally connected source for max levels if it was a dacd then confusion reigned supreme. Bring back the analogue pot.
Brian
Often they also have a push in action to fix the volume from getting moved or in some cases to set it so it comes on at that volume when turned off. Too much cleverness being built in to something that does not really need it in my view. I have one of these on a radio to move between preset stations, but the clickery bit is knackerd and now and again it has a mind of its own and moves between stations in a demented and anti social manner. Brian
Brian - bear in mind that this sopisticated changes are to benefit the manufacturer - not the user. Think how many potentiometers were saved by making remote control standard!
Many radios in cars have a setting to the switch on volume level - hidden in the settings.
I'd assumed that's why this sort of device came into use.
It also has to be a 'soft' control so a dofferent level can be used for traffic reports, etc.
Plus it allows the same knob (in conjunction with a mode button) to alter tone, balance etc.
There'e nothing quite like having multiple uses for your knob is there :-)
That is more than amusing. Its the truth.
A quality potentiometer wired into a board probably adds £1 to its final cost, and is a source of wear and short product life.
Trying to get rid of mechanical things has been a drive in electronics ever since valves went out of fashion.
I am working on a hobby project involving a piece of digital electronics that I want to control via loads of pots.
I COULD use a mouse or a touchscreen, but I like the old fashioned feel of pots...
Using that as control inputs will be the single most expensive feature in the design.
Mine just reverts to where it was when I switched off.
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