A Digispark/ATtiny85 DIY based IR (infra-red) remote control for a vintage Cambridge SoundWorks Digital CSW250 2.1 speaker system from 1999. This speaker system is connected to my TV and is responsible for the TV-audio.
The CambridgeSoundWorksDigitalIRRemote replaces the original speaker system "remote" control, which has some disadvantages:
- Cable bounded (Max. 2 meters distance)
- Without turning off the speaker system, the speaker system has an idle power consumption of about 7.5 W (even without audio input)1
- With turning off the speaker system, the system has a power consumption of about 3.1 W2
- To turn off the speaker system, the volume level has to be set to minimum volume level
- After turning on the speaker system the previous volume level has to restored manually
The CambridgeSoundWorksDigitalIRRemote allows me use the IR wireless controller from my TV to
- turn on/off the speaker system
- automatically restore the last used volume level after turning on
- change the volume level
- mute/unmute
My code and this page is licensed under the terms of the CC0 Copyright (c) 2025 codingABI.
- Board: ATTinyCore 1.5.2, LGPL version 2.1 by SpenceKonde
- Libraries:
- IRremote (4.4.1, MIT license)
- Initially coded 2009 Ken Shirriff http://www.righto.com
- Copyright (c) 2016-2017 Rafi Khan https://rafikhan.io
- Copyright (c) 2020-2024 Armin Joachimsmeyer
- IRremote (4.4.1, MIT license)
- Digispark ATtiny85 Microcontroller with reset pin configured as I/O pin
- Digital potentiometer X9C103
- IR-Receiver VS1838B
- Optocoupler 817A
- Cambridge SoundWorks Digital CSW250
- Sony KDL-40W4500 TV with Sony RM-ED011 remote controller
Warning
The CambridgeSoundWorksDigitalIRRemote was designed only for my combination: Cambridge SoundWorks Digital CSW250 and Sony KDL-40W4500/Sony RM-ED011. Other TVs/IR-Remote controls could also work, if you find the appropriate IR signals and adjust my code
Arduino IDE 1.8.19 (Without "real portable" support version 2.* makes no sense for me https://forum.arduino.cc/t/arduino-ide-2-0-portable/, arduino/arduino-ide#122 ...)
IDE-Board settings:
- ATtiny85 (Micronucleus / Digispark)
- Clock: "8 MHz (no USB)" (8 MHz reduces the power consumption)
Note
The schematic shows a female Mini-DIN-6 connector
The original remote control is cable bounded and connected by a Mini-DIN-6-Connector to the speaker system.
After analyzing the PCB I got the following schematic:
Note
The schematic shows a female Mini-DIN-6 connector
| SW1A | Reaction at the speaker system |
|---|---|
| Open | Turned off |
| Closed | Turned on (~1.3 mA between Mini-DIN-6 pin 6 and 3) |
The CambridgeSoundWorksDigitalIRRemote replaces the mechanical switch SW1A with an optocoupler.
| Mini-DIN-6 pin | Color | Connected to speaker system (my assumption) |
|---|---|---|
| 1 | Red | Ground |
| 2 | White | 5.6 V (seems to be regulated) |
| 3 | Green | Turns on/off the audio amplifier (Pin 6 and 3 connected=On, Pin 6 and 3 disconnected=Off) |
| 4 | Yellow | Audio volume level (0.76 V = Minimum volume, 5.14V = Maximum volume) |
| 5 | Blue | Not connected |
| 6 | Black | Vcc (15-18 V, when Pin 6 and 3 are not connected. Decreases to ~85%, when Pin 6 and 3 are connected) |
The original remote control uses a linear B50K potentiometer RV1. Resistor R201 changes the linear to a non linear behaviour (see the following red line).
The CambridgeSoundWorksDigitalIRRemote uses a digital, 100-steps, linear potentiometer with 10K (because I had no 50K). To get a similar non linear behaviour (Green line) and to ensures that my digital potentiometer did not get more then the allowed 5 V, I had to lower the resistors:
- R200 to 1K
- R201 to 5K1
- R202 to 2K
My Sony TV KDL-40W4500 has a "RM-ED011" IR remote control and the CambridgeSoundWorksDigitalIRRemote uses it to control the Cambridge SoundWorks Digital speaker system.
The IRremote example ReceiveDump shows me the following addresses and commands and I use some of them for the CambridgeSoundWorksDigitalIRRemote:
| Button | Address/Device Code | Command |
|---|---|---|
 | 0x01 | 0x3A |
 | 0xA4 | 0x3D |
 * | 0x01 | 0x15 |
 | 0x97 | 0x1B |
 | 0x97 | 0x1A |
 | 0x97 | 0x19 |
 | 0x97 | 0x1C |
 | 0x1A | 0x58 |
 | 0x97 | 0x18 |
 | 0x77 | 0x60 |
 * | 0x77 | 0x52 |
 * | 0x01 | 0x38 |
 | 0x97 | 0x28 |
 | 0x01 | 0x17 |
 | 0xA4 | 0x5B |
 | 0x01 | 0x25 |
 | 0x01 | 0x65 |
 | 0x01 | 0x74 |
 | 0x01 | 0x75 |
 | 0x01 | 0x34 |
 | 0x01 | 0x33 |
 | 0x97 | 0x23 |
 | 0x97 | 0x36 |
 | 0x01 | 0x60 |
 | 0x03 | 0x4C |
 | 0x03 | 0x4D |
 | 0x03 | 0x4E |
 | 0x03 | 0x4F |
 * | 0x01 | 0x00 |
 * | 0x01 | 0x01 |
 * | 0x01 | 0x02 |
 * | 0x01 | 0x03 |
 * | 0x01 | 0x04 |
 * | 0x01 | 0x05 |
 * | 0x01 | 0x06 |
 * | 0x01 | 0x07 |
 * | 0x01 | 0x08 |
 | 0x01 | 0x3F |
 * | 0x01 | 0x09 |
 | 0x77 | 0x76 |
 * | 0x01 | 0x12 |
 * | 0x01 | 0x13 |
 * | 0x01 | 0x10 |
 * | 0x01 | 0x11 |
 * | 0x01 | 0x14 |
 | 0x01 | 0x3B |
*TV can be turned on with this button
The CambridgeSoundWorksDigitalIRRemote gets its 5 V supply voltage from the USB port of my Sony-TV. When the Sony-TV is turned off about ~22 minutes later the USB port will be automatically disconnected.
Before disconnecting the 5 V supply voltage, the power consumption of the CambridgeSoundWorksDigitalIRRemote is dependent on the used voltage on the Digispark "5V"-pin, the clock speed and sleep mode:
| "5V"-pin voltage | Clock speed | Sleep mode | Power consumption | Comment |
|---|---|---|---|---|
| 5.0 V | 16.5 MHz, tuned of USB (USB) | none | 116 mW | 5 V from TV connected to "5V"-Pin of the Digispark |
| 5.0 V | 16.5 MHz, tuned of USB (USB) | SLEEP_MODE_IDLE | 93 mW | 5 V from TV connected to "5V"-Pin of the Digispark |
| 5.0 V | 8 MHz (no USB) | none | 96 mW | 5 V from TV connected to "5V"-Pin of the Digispark |
| 5.0 V | 8 MHz (no USB) | SLEEP_MODE_IDLE | 80 mW | 5 V from TV connected to "5V"-Pin of the Digispark |
| 4.7 V | 8 MHz (no USB) | SLEEP_MODE_IDLE | 70 mW | 5 V from TV connected to Digispark USB port (My Digispark uses a S4 Schottky diode with a forward voltage of ~0.3 V)3 |
| 4.3 V | 8 MHz (no USB) | SLEEP_MODE_IDLE | 65 mW | 5 V from TV connected via a 1N4007 diode to "5V"-Pin of the Digispark4 |
Below 8 MHz the ATtiny85 can not receive IR signals from my Sony RM-ED011 (At least with the used library IRremote).
As as result of this table the CambridgeSoundWorksDigitalIRRemote uses 4.3 V, "8 MHz (no USB)" and SLEEP_MODE_IDLE
=> 65 mW power consumption5.
My Digispark clone uses pin 5 as a reset pin. To use this pin as an I/O pin I had to change a fuse:
hardware\tools\avr\bin\avrdude.exe -P com4 -C hardware\tools\avr\etc\avrdude.conf -b 19200 -c avrisp -p attiny85 -n
hardware\tools\avr\bin\avrdude.exe -P com4 -C hardware\tools\avr\etc\avrdude.conf -b 19200 -c avrisp -p attiny85 -U hfuse:w:0x5F:m Warning
After that the Digispark can only be programmed by a USB-micronucleus-bootloader or a high voltage programmer!
Pin 5 is a "weak" pin and can not provide as much power as the other I/O pins, but can provide the needed ~1.5 mA to drive the used optocoupler.
Footnotes
Replacing the original power supply TEAD-66-153000V with a smaller/newer 15 V power supply (for example https://www.amazon.de/dp/B0D2K7L311?ref=ppx_yo2ov_dt_b_fed_asin_title) reduces the idle power consumption to 3.8 W ↩
Replacing the original power supply TEAD-66-153000V with a smaller/newer 15 V power supply (for example https://www.amazon.de/dp/B0D2K7L311?ref=ppx_yo2ov_dt_b_fed_asin_title) reduces turned off consumption to ~0 W ↩
"Pin high" voltage for pin 5=2.4 V, optocoupler If=1.6 mA, Ic=1.3 mA, Uceo=0.2 V ↩
"Pin high" voltage for Pin 5=2.2 V, optocoupler If=1.4 mA, Ic=1.1 mA, Uceo=1.8 V (not optimal, but working) ↩
Most of the power is not consumed by the ATtiny85. About 75% is consumed by the other used electronic components (Builtin LED, driving the optocoupler, digital potentiometer, USB data lines,...) ↩