Prototype physical volume knob for Tesla-style PX6 Android headunit (1 Viewer)

[binaryaudax]

In the time I've had the PX6 Android unit installed in my GX470, I've been frustrated with the lack of a physical, rotating volume knob. The on-screen volume control is hard to locate while driving even for passengers.

I've seen a few posts in the PX6 Facebook group about using a Bluetooth media controller with a volume knob in the cup holder, but I didn't want to give up a cup holder. I also wanted something that could almost pass for being OE/factory.

Here's my work-in-progress to solve this problem.

I added a rotary knob to the left side of the unit which required disassembling the unit and drilling through the bezel.

In an early attempt, I connected the knob to an Arduino microcontroller that acted as a USB keyboard. The worked, but unfortunately, it would only control the media volume settings within Android, not the DSP/amplifier in the unit. The Android media volume range doesn't have many steps from minimum to maximum volume -- only about 15 steps if I remember correctly. I had to ditch that method.

The second (and current) attempt is an Arduino microcontroller that mimics the steering wheel buttons being pressed. This is working perfectly so far. The rotary knob I'm using also acts as a push-button, so I've wired it up to act as MUTE when the knob is pressed.

Here's a video in action: (sorry for the portrait mode, I was trying to fit everything in frame)




The next step is to turn my prototype schematic into a real printed circuit board.

 

[ArBrnSnpr]

That's so, so far outside of my capabilities!
Well done!

 

[jdevtac]

I’d totally buy one if you decide to sell. The lack of a physical knob drives me nuts.

 

[binaryaudax]

I’d totally buy one if you decide to sell. The lack of a physical knob drives me nuts.

I'm definitely open to selling to people that are comfortable with do-it-yourself solutions. The circuit board would be assembled but drilling and mounting the rotary knob would be up to you.

 

[jdevtac]

I'm definitely open to selling to people that are comfortable with do-it-yourself solutions. The circuit board would be assembled but drilling and mounting the rotary knob would be up to you.

Yeah thats no problem with me. I was toying with getting a knob to begin with but hadn’t seen one I liked. Most of the generic usb ones are larger diameter. This one looks perfect. My only question is last time I pulled my Tesla unit it looked like the android assembly metal casing was sitting over the plastic. Did you have to drill through that too or remove?

 

[binaryaudax]

Yeah thats no problem with me. I was toying with getting a knob to begin with but hadn’t seen one I liked. Most of the generic usb ones are larger diameter. This one looks perfect. My only question is last time I pulled my Tesla unit it looked like the android assembly metal casing was sitting over the plastic. Did you have to drill through that too or remove?

A USB device acting as an HID-compliant device like a multimedia keyboard won't control the "correct" volume. It'll control the media volume for Android, but that not the same as the amplifier volume control for these PX6 units (controlled via steering wheel and the bottom navigation panel).

Yes, there is metal casing there but it's easily removed... only a half dozen screws. It's just shielding over the back too, so when it's removed it doesn't pull any electronics with it -- just the metal shield.

Metal casing removed, hole drilled and knob test fitted:

Secured with a nut on the front, some Kapton tape on the back and connector secured:

 

[BillZ260]

In!

 

[binaryaudax]

PCB is wrapping up production now and should be in my hands early next week. Once I test it successfully, I'll have 3-4 spares for sale.

 

[BillZ260]

Can you post pics of where you plugged this into the. Wiring of the unit? I have a pre 03 and don't have steering wheel controls, wondering if this will work for me too.

 

[binaryaudax]

Can you post pics of where you plugged this into the. Wiring of the unit? I have a pre 03 and don't have steering wheel controls, wondering if this will work for me too.

Sure thing. I'll snap more pictures when the production boards arrive and I install the final product. I'd imagine the steering wheel wiring is probably there even if you don't have the buttons, but I'd need to look at a 03 wiring diagram to be sure.

 

[jdevtac]

A USB device acting as an HID-compliant device like a multimedia keyboard won't control the "correct" volume. It'll control the media volume for Android, but that not the same as the amplifier volume control for these PX6 units (controlled via steering wheel and the bottom navigation panel).

Yes, there is metal casing there but it's easily removed... only a half dozen screws. It's just shielding over the back too, so when it's removed it doesn't pull any electronics with it -- just the metal shield.

Metal casing removed, hole drilled and knob test fitted:
View attachment 2435932

Secured with a nut on the front, some Kapton tape on the back and connector secured:
View attachment 2435931

Right, that’s what stopped me from getting a knob also and in reading your original post too. I’d like to control the overall volume rather than the android media volume.

PCB is wrapping up production now and should be in my hands early next week. Once I test it successfully, I'll have 3-4 spares for sale.

View attachment 2436427

Definitely interested!

 

[BillZ260]

Basically I have a usb knob right now, but it only controls android functions on Volume, not the radio or BT functions

 

[binaryaudax]

Boards arrived today. I assembled one and tested it successfully. Need to find a project box to enclose it and mount it behind the headunit.

 

[jdevtac]

I’ve been wondering, if you can make a knob control the amp volume via interfacing with steering controls, is it possible to make a knob to control AC fan speed? Considering that the custom firmware by Sergey is able to make fan speed selections via steering controls, I’m guessing there has to be some sort of input to do this with a physical knob also. I just feel like that would be the ultimate setup, essentially having near full manual HVAC control.

 

[binaryaudax]

I’ve been wondering, if you can make a knob control the amp volume via interfacing with steering controls, is it possible to make a knob to control AC fan speed? Considering that the custom firmware by Sergey is able to make fan speed selections via steering controls, I’m guessing there has to be some sort of input to do this with a physical knob also. I just feel like that would be the ultimate setup, essentially having near full manual HVAC control.

Yes, I definitely think that is possible. The "brains" of the HVAC system is not part of the headunit or the factory nav display/radio -- it's elsewhere under the dash. The display in the center console just communicates with the A/C ECU to make fan speed, temp, blend door, etc changes.

I'm actually working on a separate project in parallel that would display the current A/C status in the "accessory meter" (the clock/mileage/altimeter/barometer unit above the center console.

I've never tried to control the fan speed from the steering wheel buttons like you mentioned but I'm aware its possible -- I usually leave my A/C in Auto mode. I think it may just be a matter of long-pressing the button. I'll look into that more...

 

[zml]

This is totally interesting!
I’m looking for a head unit for my Suzuki Vitara but they all don’t have a volume dial.
So I would love to add a dial like you did.

Do you connect your Arduino output in parallel with your steering wheel buttons? And if so, how do you do that? Do the SW1 & SW2 used as the button simulation output?
Can you share your Arduino code and PCB schematics?

 

[binaryaudax]

Do you connect your Arduino output in parallel with your steering wheel buttons? And if so, how do you do that? Do the SW1 & SW2 used as the button simulation output?
Can you share your Arduino code and PCB schematics?

Yes, I just tapped into the steering wheel button signal wires using t-tap quick connects.

The schematic and Arduino source are up on GitHub here: ryanmcdonnell/arduino-volume-control - https://github.com/ryanmcdonnell/arduino-volume-control

Good luck!

 

[zml]

Thanks!
I already have small Arduino and a rotary + click encoder, so I only need to order the MCP4231.

Can you explain how both volume down and mute use the same 3.2Kohms and what this left/right PadAddress?
To get the resistant values for the commands have you measured the resistant from the two steering wheel wires while pressing the corresponding buttons?
Why do you use the 74hc14 and the capacitors? Usually I see that they are connected directly to the Arduino.

I also found another nice example for adding buttons to the head unit here

 

[binaryaudax]

The capacitors and the 74hc14 are used to hardware denounce the input from the rotary encoder and its push button. The encoder and button can be noisy and trigger rising/falling multiple times. Software debouncing would be an option, but I prefer to handle it more reliably with hardware and keep the code clean.

I found the resistance values for the steering wheel buttons by looking at the electrical repair manual for the GX. The troubleshooting process for non-working buttons included a table of all the resistance values for each button.

The GX470 has buttons on the left and right side of the steering wheel, hence the left and right pad addresses in code. Each side is a separate input signal from the steering wheel to the headunit.

 

[koobz]

@binaryaudax reviving an old thread, but one of my climate buttons is broken. You reckon I can source something from e.g. digikey and replace it? I imagine you might have some insights given what you did with this mod.