Automatic temperature control for fans attached to a Raspberry Pi running FPP

• A stand-alone version of PID_Fan_Control (not dependent on FPP) can be found in the stand-alone branch
• The Wikipedia article on PID controllers <https://en.wikipedia.org/wiki/PID_controller>
• The temperature is actually coming from the GPU, but the GPU and CPU temps should be roughly the same
• The PiFace ULN2803A is only capable of driving 500mA max on each output, so if you need to drive a high power fan, appropriate drive circuitry must be added to the output
• If driving a two or three wire 12V fan directly from a PiFace output, you will need to remove jumper 4 (disables built-in snubber diodes connected to +5V) or you risk damaging your PiFace. You will also need to use a snubber diode across the fan motor's windings to prevent inductive kickback from causing problems. If driving a four wire (PWM) fan, the current source only needs to supply 5mA, can use 5V and does not require a snubber diode or the removal of jumper 4.

The adjustable parameters are:

• -l LOG, --log LOG The file to write the logs to. Default is /home/fpp/media/logs/pid_fan_control.log.
• -p PWM_PIN, --pwm_pin PWM_PIN This parameter sets the GPIO output to use for PWM. Default is 202 (PiFace output #3)
• -t TEMP, --temp TEMP This is the target temperature in Celsius. Default is 45.0
• -i, --invert This parameter is used to invert the duty cycle which is needed if using open collector outputs (like the PiFace) to drive a four wire (PWM) fan. Default is False.
• -m MIN_SPEED, --min_speed MIN_SPEED This parameter is used to set the minimum duty cycle. Some fans do not spin with the duty cycle below certain values, and this allows setting a minimum value to avoid this. Default is 0.
• -o, --min_turn_off This parameter works in conjunction with MIN_FAN_SPEED to turn off the fan when the target duty cycle reaches 0. Default is False.
• -d, --on_off Set to True to use dumb mode i.e. on or off when PWM is not supported by the selected GPIO. Default is False.
• -v, --verbose Verbose logging. When enabled, this parameter instructs the program to log additional details during run time which can be helpful when setting up new fans, or tuning parameters. Default is False.
• -T VERBOSE_TEMP_THRESHOLD, --verbose_temp_threshold VERBOSE_TEMP_THRESHOLD When using verbose logging, the amount the temperature must change (+-) to write to the logfile if the duty cycle has not changed. This can be helpful if using the logs to monitor the fan/temperature performance. Default is 1.0

FPP users: to make the script run as a daemon, follow the instructions below.

1. Upload the two python (.py) files and the init script (PID_fan_control.sh) to your FPP scripts directory (/home/fpp/media/scripts)
2. SSH in to your FPP.
3. Manually run the PID_fan_control.py script to ensure it works properly, and add/adjust any configurable parameters via command line options. It may be helpful to enable verbose logging (--verbose) to see more details while running. You can view the logs in the FPP log directory under the name PID_fan_control.log.
4. Only once you are satisfied with the settings, continue to the next step.
5. Make the init script executable with 'sudo chmod 755 /etc/init.d/PID_fan_control.sh'
6. Edit the init script and add any desired command line arguments to DAEMON_OPTS. e.g. DAEMON_OPTS="--min_speed 85 --min_turn_off"
7. Add the PID_fan_control.sh script as a preset for FPPD_STARTED with script arguments start and test (check PID_fan_control.log)
8. Add the PID_fan_control.sh script as a preset for FPPD_STOPPED with script arguments stop and test (check PID_fan_control.log)
9. Restart fppd and ensure the daemon is running by checking the latest log entries.

1. Upload the Perl script (read_fan_stats.pl) to your FPP scripts directory (/home/fpp/media/scripts)
2. While logged in via SSH, install the snmp and snmpd packages with sudo apt-get install snmpd snmp.
3. Use your favorite text editor to modify agentAddress in /etc/snmp/snmpd.conf from agentAddress udp:127.0.0.1:161 to AgentAddress 161
4. Set the read-only snmp community string to public by adding rocommunity public below the #rocommunity public localhost line.
5. Add the following line towards the bottom of the file: extend pidfan1 /usr/bin/perl /home/fpp/media/scripts/read_fan_stats.pl /home/fpp/media/logs/pid_fan_control.log
6. Restart the snmpd daemon with sudo service snmpd restart
7. The temperature setpoint, current temperature and fan speed are now available on the following OIDs:

• temperature setpoint: .1.3.6.1.4.1.8072.1.3.2.4.1.2.7.112.105.100.102.97.110.49.1
• current temperature: .1.3.6.1.4.1.8072.1.3.2.4.1.2.7.112.105.100.102.97.110.49.2
• fan duty cycle: .1.3.6.1.4.1.8072.1.3.2.4.1.2.7.112.105.100.102.97.110.49.3

• This application was initially based on pidfanpi: https://github.com/SimplyAutomationized/raspberrypi/tree/master/pidfanpi
• Extensive re-use of example code from http://blog.scphillips.com/posts/2013/07/getting-a-python-script-to-run-in-the-background-as-a-service-on-boot/