Raspberry Pi Notes

Raspberry Pi Notes.txt

 Setting up a SD card for a headless configuration
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 	To...                In "/boot" place:
	⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻     ⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻
 	Enable SSH       --> ssh.txt (empty)
 	Create User      --> userconf.txt (contents: pi:$6$c70VpvPsVNCG0YR5$l5vWWLsLko9Kj65gcQ8qvMkuOoRkEagI90qi3F/Y7rm8eNYZHW8CY6BOIKwMH7a3YYzZYL90zf304cAHLFaZE0) <-- pi:raspberry
 	configure wifi   --> wpa_supplicant.conf

	To generate a userconf.txt file
	⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻
	Paste this into a bash shell:
	   (read -p "Username: " username; read -p "Enter password:  " password; read -p "Verify password: " password2; [ "$password" = "$password2" ] || { echo "Passwords do not match!"; exit 1; }; printf "%s:%s" "$username" "$(openssl passwd -6 "$password")" > userconf.txt; )
 	

	To generate a wpa_supplicant.conf file
	⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻
	Use the following command on a linux machine (you will be prompted for a password):
	   wpa_passphrase 'network-ssid' > wpa_suplicant
	


 Running a script on startup without login
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    crontab -e
    @reboot <command> &

    see: https://www.raspberrypi.org/documentation/linux/usage/cron.md


 Overclocking (pi4)
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	In /boot/config.txt
	⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻
	# uncomment to overclock the arm. 700 MHz is the default.
	over_voltage=6
	arm_freq=2000


 Monitor cpu temp and throttling
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	watch -n 1 vcgencmd measure_clock arm
	watch -n 1 vcgencmd measure_temp
	watch -n 1 vcgencmd get_throttled
	--or--
	watch "vcgencmd measure_clock arm; vcgencmd measure_temp; vcgencmd get_throttled"




 Prevent Kernel Upgrades
 ‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
	sudo apt-mark hold libraspberrypi-bin libraspberrypi-dev libraspberrypi-doc libraspberrypi0
 	sudo apt-mark hold raspberrypi-bootloader raspberrypi-kernel raspberrypi-kernel-headers



 Create a compressed image from an SD card
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	to create an image:
 		sudo zstd /dev/mmcblk0 -f -o FILENAME.img.zstd

 	to restore image:
	 	sudo zstd -df FILENAME.img.zstd -o /dev/mmcblk0

	(replace /dev/mmcblk0 with your SD card's device)

	note: Use e2image to create sparse disk images


 Set status LED pattern
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	echo "<pattern>" | sudo tee /sys/class/leds/led0/trigger

	where <pattern> is one of:
		actpwr     (sold on)
		timer      (blinking)
		heartbeat  (heartbeat pattern)
		none       (off)

	a complete list of available patterns is available via:
		cat /sys/class/leds/led0/trigger
		
	NOTE: The pi0 uses a act instead of led0
	
 Manipulate PWM output via /sys (from a shell)
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 	Works for hardware PWM (gpio-18[pwm0], and probably 13[pwm1])
 	
	Setup:
		# Set these variables to configure PWM
		frequency=1000    # is 1000hz
		duty_cycle=25     # is 25%
		
		# Do some math and set
		period="$((1000000000/$frequency))"
 		echo "$period"                      | sudo tee /sys/class/pwm/pwmchip0/pwm0/period     > /dev/null
 		echo "$(($period*$duty_cycle/100))" | sudo tee /sys/class/pwm/pwmchip0/pwm0/duty_cycle > /dev/null

	Changing duty cycle:
		duty_cycle="30"
		
		period="$(cat /sys/class/pwm/pwmchip0/pwm0/period)"
		echo $(($period*$duty_cycle/100)) | sudo tee /sys/class/pwm/pwmchip0/pwm0/duty_cycle > /dev/null