Controlling potentiometer volume with push buttons?

[dw2296]

Hi, I am working on a car project. Basically, I need to be able to control the volume of the radio (a knob/pentiometer system I think) with two push buttons: one for up, one for down. I am still relatively new to electronics and have no idea where to start, without causing the volume to be dependent upon both switch systems. They need to be independent, such that either one can be used to adjust the volume throughout the whole range. I'm not sure how to do this. How is this done on factory car sound systems equipped with things like steering wheel controls?

PS: the push button signals will be going through a microcontroller first to interpret the resistive mulitplexing, in case that opens up possibilities.

Any help is much appreciated. Thanks!

 

[BradtheRad]

knob/pentiometer

Can you state which of two types this is? Either (a) rotates endlessly, or (b) traditional type with stops at the max and minimum levels?

If it's the second type then you have a difficult job to make it cooperate with up/down buttons.

 

[dw2296]

It's the endlessly rotating kind.

I haven't taken it apart yet, so I apologize if I've given any wrong info.

 

[doraemon]

Hello!

One possible system would be to use an encoder. Not mechanical of course. Mechanical encoders
are very unreliable when they get old. For instance a magnetic encoder. From there, you can detect
the variation direction in order to set the level up or down. And you can do the same in parallel
with your buttons. Don't use mechanical buttons for the same reason as above. Use capacitive
sensors. If your volume controller can receive messages from both the knob and the buttons,
then you can increase with the knob, then increase with the buttons from the same level, everything
should run smoothly.
And I was about to forget: you can use SPI (or I2C) controllable analog potentiometer to actually
control the sound.

Pascal

 

[KlausST]

Hi,

Taking just the information of your headline gave me the idea of a motor-potentiometer, where with two pushbuttons you may run the motor forward or backwards.

Klaus

 

[FvM]

It's not clear to me which part of the "car project" you want to design. In case you are using off-the-shelf car audio components, which control interfaces you intend to use?

Be sure that recent car radios and car audio systems are using digital control for everything, e.g. the sound level. So it can be basically remote controlled through car busses. The sound level will be most likely represented by a digital number which can be read and written, an up/down button control would utilize a microcontroller for translation. Alternatively the control could be provided by incremental up and down commands. A microcontroller would be needed as well to talk to the bus.

 

[dw2296]

Thanks for all the help so far, everyone.

I guess I should give some background info on the project itself. I am trying to add steering wheel radio controls to the vehicle. It's a '95 Jeep Grand Cherokee. So far, I've pretty much figured out how to get the signals from the wheel to the dash (The '96 model uses resistive multiplexing to do this, which I am basically copying, thus the Arduino).

First, I have NO idea what a magnetic encoder is, so I will read about that. That sounded promising.

I thought about the motor, but didn't like the idea since the knob on the radio would be physically turning itself (right?), and that's besides the need to power the motor. The knob also makes audible clicks when turned.

About the digital stuff, I do think that's how it's controlled with the systems that came with steering wheel controls. I have a '95 model, which didn't have the option for the steering wheel controls. The '96 year models had very different electronics, and the steering wheel control info went through the data bus first. There is a two-pin plug on the back of the radio through which the bus communicated things such as the steering wheel commands among other info. I have no idea what kind of signals are sent through those two wires, or else I could probably just duplicate them. I was thinking it would be easier to just open up the radio, hard-wire the circuits to the individual buttons and add another plug behind the radio for all this. That way I could just use the Arduino and maybe some PCB relays to complete circuits as desired. Everything should be easy except for the volume knob.

 

[dw2296]

Alright, so there is my incremental rotary encoder, and I also found that coding chart. I'm still trying to understand how it works though. Using my multimeter, either NEITHER A and B are grounded, or BOTH A or B are grounded. It flip-flips between those two states every click of the knob. For clockwise rotation, this is phases 1 and 3 I think, respectively. Does this mean that there are momentary pulses in between the clicks that I'm just not picking up?

In terms of coding this in the Arduino, I feel like it's more complicated than simply following the chart. I am thinking that I might have to read the position of the physical switch first, then use that info to decide which pin gets momentarily pulsed, depending on the direction I want to go. But would that confuse the radio? For example, if the physical knob is in a position where NEITHER A and B are grounded, and I want to volume up using the push button. I guess then I would momentarily ground B (do I delay here?), then simultaneously ground both A and B. I don't know if that would actually increase volume at that point or not. But if it does, do I just leave them both grounded (which may or may not confuse the radio), or do I go straight back to the physical knob's state of both pins being ungrounded?

Please let me know if I have this all mixed up.