The MacOS portion of this software is based on https://github.com/passatgt/imac-pwm-control and has been rewritten to communicate via USB-serial with an ESP32 microcontroller hooked up to your iMac.
The 2009–2011 iMacs are nicely upgradeable, thanks to many MacRumors members (especially Nick [D]vB) it is possible to even run rather recent graphics cards on these old iMacs. The problem is that iMacs run custom GPU vBIOS (video BIOS) software from Apple that, among other stuff, enables backlight control. So when you upgrade your graphics card, you lose backlight control, even with Nick [D]vB's custom vBIOS for many cards. You can regain backlight by running OpenCore but just doing it in hardware seemed like a safer longer term bet.
Install Micropythpon and use Adafruit's ampy to put the files in ./micropy/src/*.py onto the ESP32.
Restart the ESP32 and make sure the blue LED turns on as well. Possibly connect via Picocom or another terminal emulator to the ESP32's serial USB port and type in a number to adjust the LED (and PWM sigmal) brightness, 0 => 0%, 100 => 100% brightness.
Install the ESP32 inside your iMac, get a short 6-pin PCI-e male to female extension cable and cut the PWM line (looking at the back of female connector, it's the bottom right wire) and disconnect the original PCI-e cable to the LCD controller board, insert the extension cable and hook up original to extension. Run that cut wire to your ESP23 to GPIO23/D23 pin. Connect the ESP32 to an external USB port for testing, you can later wire it to your internal IR port (which is also a USB port).
Install the SiLabs USB VCP drivers for the ESP32 USB/serial port. Build the MacOS app or download from releases and run, configure the serial port in the settings and baud rate (usually "/dev/cu.SLAB_USBtoUART" and "115200") and click done. The app needs access to Accessibility to intercept the Mac keyboard brightness keys, you can also just use the slider
But don't just copy&paste this, read INSTRUCTIONS.md and adjust these steps as needed to your own system.
- Install/download the necessary software
- Homebrew
- Micropython esp32-idf4–20191220-v1.12.bin (version tested)
- SiLabs USB serial drivers
brew install pip3 esptool.py picocom- MacOS Brightness controller from releases in this repo
pip3 install adafruit-ampy
- Flash and program the ESP32
- Install SiLabs drivers and connect ESP32s
- Flash micropython:
/usr/local/bin/esptool.py --port /dev/cu.SLAB_USBtoUART erase_flashthen immediately on the ESP32-D1 dev kit, hold down “BOOT” first, then briefly press “EN”, then/usr/local/bin/esptool.py --chip esp32 --port /dev/cu.SLAB_USBtoUART --baud 460800 write_flash -z 0x1000 ~/Downloads/esp32-idf4-20191220-v1.12.binand repeat BOOT + EN as before - run
./micropy/install_mac.shfrom the GitHub repo local clone to put the files on the ESP32, reboot the ESP32 and check that the blue LED is on
- Wire up the 6-pin PCI-e extension cable to the LCD controller board, cut the PWM wire and route the PWM wire to your ESP32 pin D23/GPIO23.
- Wire up your ESP32 to the iMac's internal IR USB port or run a cable to the back of the iMacs normal USB ports.