fancontrol

This project aims at controlling a standard 4-PIN fan based on the surrounding temperature. It mainly relies on the GPIOs of the Raspberry Pi B+.

The main goal here is for me to discover the joy of low-level programming on an embedded ARM architecture.

I'll try to add a self-sufficient makefile to build a minimalist ramfs distro through Buildroot to to make it look like a real embedded system.

Setup

Toolchain requirements

This project requires the following points in order to work :

• A toolchain located in /opt/armv6-rpi-linux-gnueabihf/bin/arm-linux-gnueabihf- or the toolchain in your PATH
• A rootfs directory in /opt/armv6-rpi-linux-gnueabihf/ (lib and include)
• A kernel source code for linux 4.14 in /opt/kernel/linux-rpi-4.14.y
• You can build your own toolchain with the configuration file .config-cross in the tools/boot directory
• You may need to edit some path and some settings before compiling the toolchain.

On your Pi

• Use the version 4.14.70 for your kernel
• Install at least tmux on your Pi
• Copy the scripts in tool/scripts on your Pi
• Add the ltmux.sh script to your init sequence

Alternatively, you can use the buildroot .config file present in the tools/boot directory

• You need to edit the path to the .config-linux file in the buildroot configuration
• You need to edit the path to the overlay filesystem that include the script ran at startup
• You can mount the partitions on your SD card for persistent file storage. The first partition is automatically mounted.
• You need a fancontrol directory containing the software and the kernel drivers on your first partition (the one with the zImage file).

Security

• Do not forget to change the root password in the .config file for buildroot under "System configuration" or with the BR2_TARGET_GENERIC_ROOT_PASSWD variable
• You can generate the keys for dropbear to avoid generating random ones at each startup with the following commands :
  • dropbearkey -t ecdsa -f /path/to/your/rootfs/etc/dropbear/dropbear_ecdsa_host_key
  • dropbearkey -t rsa -f /path/to/your/rootfs/etc/dropbear/dropbear_rsa_host_key
• Git will ignore any keys you put in the directory for the dropbear keys to avoid pushing them online

About

Control the fan's speed

• Use of the PWM pins on the Raspberry Pi to control the 4-PIN fans
• Separation between command and power circuits.
• Reading of the actual speed of the fan through IRQ

Measure the temperature

• Configure an AD7705 ADC through SPI
• Measure the temperature using a thermistor

Drive the software via interrupts

• Use of custom drivers listening on GPIOs state to deliver interrupts to run the software

Schematics

Circuit layout

• Coming soon...

RPi's pins layout

• Coming soon...