Volume Control Knob for Your Android Automotive Touch Screen Radio

Want to be able to change the volume of your touch screen radio without pressing the screen.. This project will let you add a rotary knob to alter the volume with very few parts.

Parts used:

1 Arduino device. (U1) I'm using an ATMega 328, but you can use an Arduino UNO or Mini or the like.

1 74HC14 (U2), hex Schmitt trigger

1 CD4066 (U3), quad bilateral switch

sockets for dip IC's (optional)

perf PCB

few resistors

R1,R2, R4, R11, 10k ohm

R3, 2k ohm ( used for MUTE function )

R7, R8, R10, 1k ohm ( R10 used for VOLUME +, R7 and R8 for green leds D1, D2)

R9, 500R (ohm) (used for VOLUME -)

R12, 220R (ohm) ( used for red power led)

C1,C2,C3, C6, capacitors 104, or 0.04 uf

C4,C5, capacitor 220, ( used by the Xtal )

D1, D2, green leds ( Volume +, - indicators )

D3, red led ( power)

Xtl1, 16 Mhz crystal

SW1, EC-11 encoder switch

The circuit

Switch 1 is a 2 channel (mechanical) rotary encoder switch with a centre push button mom, N.O. part # EC-11.

Its outputs are buffered via U2 a SCHMITT trigger # 74HC14 or equivalent .

U2's outputs are fed into i/o pin 2 and 3 on the ATMega (U1) or (an Uno). or equivalent.

U1's Outputs i/o 7, 8 go to U3 the Quad Bi-lateral switch (U3). to control the 2 resistors (R9, R10) that act like steering wheel controls buttons. NOTE the resistor values for R9, R10 can be pretty much anything as the radio will learn that specific value when you do the settings programming on the radio. My R9 R10 values might conflict with yours, if so find a resistor value that works for you by trial and error.

Green leds D1, D2 are activated by 2 gates from the 7414 and i/o 7,8 as well. They light up for each "click" of the encoder switch. Gives you a visual of what the 4066 is doing.

Hooking up to the radio

On the back there is the connector "A", its a 16 pin with free ends or possibly connectorized , locate wires pin 1 and pin 4. It should be labelled "KEY 1" or "KEY 2", pick either one makes no difference.This is the wire that would normally go to the steering wheel buttons. Wire 1 is a ground , this is connected to J2 pin 2 in my circuit and pin 4 (key) goes to J2 pin 1.

If you are keeping your steering wheel buttons in play, as mentioned before my resistor values might conflict with your values. I would suggest you find your Vol+,- buttons resistor values for your specific car and match them to my circuit R9, R10.

This project acts like a remote relay pressing the Vol + and - on the steering wheel.

Activating the encoder functions to the radio

In the touch screen,

Find SETTING function button on the radio, navigate to FACTORY SETTING, enter the password ( mine was 1,2,3,4 ), then press PARTY CONTROLS again yours might be called something different, find the VOLUME - button, press it to activate it, it should indicate that its waiting for a response from you by changing colours , now SPIN ( turn) the encoder shaft CCW a few clicks and the radio should acknowledge that its confirmed, do this again for the VOL + spin the shaft CW, and again radio should OK that button, and lastly the MUTE , press the encoder PB and hold for a few seconds until radio OK's that button.

Your done, exit back to main screen, try your new Volume control. Green Leds should be blinking when shaft ( clicks ) are felt.

There is no led indicator for the Mute PB, you could add one, and use one of the spare gates on U2 to drive it.

My prototype PCB overlay is a laser printed page stuck to a blank board, drilled and mounted the components. Some might notice more parts than I describe / use in the schematic, this is because i had other features that im not using here. Such as secondary PB buttons and a reset sw.

PS This circuit works great, MAKE SURE that you connect to the proper KEY1, or KEY2 wires. Not responsible for you shorting out your outputs on the radio.

Enjoy

Dan