Intro

This is the opening salvo in my 4 project push. Rather than simply presenting a chronological documentary or a report format with objectives and dry design documents, I wanted to make it a bit more interactive, so I presented pictures of the system for viewers to creatively deduce what they were looking at. This added a lot of interesting ideas to the blog comments. This blog is now updated, including a new title (to make the blog more searchable) and information identifying what the project does. I would like to thank the commenters for making this simple project into a more interesting and entertaining blog. 

This project was a result of my need for volume control of the speakers on my PC. The speakers have a volume control, but it is in an awkward location. I wanted something more convenient. My keyboard actually has function keys that can control volume, but I also find that an awkward method of volume control. It requires 2 keys to be pressed multiple times to reach a desired volume. The device shown here is an intuitive volume knob that can be positioned very conveniently. And I use it every day.

These are the clue images

• this view does not show any cables....

Here is the second image - showing an additional surface with the usual feline photobomber...

The next image will show the PCBs inside...

Okay - here is the exploded view....some of it should be quite recognizable...

Note how the main PCB slides into a slot making the set screw in the knob the only fastener in the system.

I had to play hockey this evening, so I didn't get around to a more complete description of the system, but I will try again tomorrow.

In the mean time - here is another picture of the assembled system....

Project Description

This device is a simple volume control for PC speakers.

It uses a Raspberry Pi Pico to read a mechanical rotary encoder and convert the rotation into HID keyboard volume control commands sent to a host PC via USB.

The Pi Pico is mounted on a custom PCB which simply provides connections between the Pico and the encoder.

Here is a schematic of the relevant connections:

Schematic

Firmware

# Pi Pico Volume Contrroller by Doug Wong 2025
# Pi Pico HID volume firmware
# This program reads a mechanica rotary encoder that generates a quadrature signal on 2 pins
#  the up or down pulses are sent to the host computer via a HID USB driver that emulates a keyboard
#  the HID commands are volume controol instructions

# import libraries
import usb_hid
import board
import digitalio
from adafruit_hid.keyboard import Keyboard
from adafruit_hid.keycode import Keycode
from adafruit_hid.consumer_control import ConsumerControl
from adafruit_hid.consumer_control_code import ConsumerControlCode

# Define pin numbers for the rotary encoder 
CLK_PIN = board.GP16
DT_PIN = board.GP17
SW_PIN = board.GP18

# debouncing variables
clk_last = None
count = 0
 
keyboard = ConsumerControl(usb_hid.devices)

# Define Encoder pins
clk = digitalio.DigitalInOut(CLK_PIN)
clk.direction = digitalio.Direction.INPUT
 
dt = digitalio.DigitalInOut(DT_PIN)
dt.direction = digitalio.Direction.INPUT
 
sw = digitalio.DigitalInOut(SW_PIN)
sw.direction = digitalio.Direction.INPUT
 
# Define USB HID volume control commands
def ccw():
    print("CCW")
    keyboard.send(ConsumerControlCode.VOLUME_DECREMENT)
 
def cw():
    print("CW")
    keyboard.send(ConsumerControlCode.VOLUME_INCREMENT)

# Endless loop to read encoder and send volume commands 
while(1):
    clkState = clk.value
    if(clk_last !=  clkState):
        if(dt.value != clkState):
            cw()
        else:
            ccw()
    clk_last = clkState;

Discussion

This volume control device is a very simple build that uses parts I already had lying around. Normally I probably wouldn't design a PCB board just to connect an encoder, but I had a PCB that already included the right connections. I enjoyed the simplicity of the build and I really enjoy the convenience it provides for a function I use every day. One thing I may do to improve this device is to replace the knob with a more massive knob that would allow it to be spun and have its momentum continue spinning until it is stopped.

Again, I would like to say I enjoyed the interesting comments in response to the mystery images.