SSH Lag on RPi...

On a new install, there was a strange lag in SSH, where it would repeatedly freeze...

The solution appears to be to update /etc/ssh/sshd_config to set:

   ClientAliveInterval 60
   ClientAliveCountMax 10

and or in /etc/ssh/ssh_config:

   ServerAliveInterval 60
   ServerAliveCountMax 10

The server is the host that receives the connection...

These are taken from here...

Pi4j Releases

Note that Pi4j v1.4 relies on Java 11, whcih will cause issues with older models of Raspberry Pis.

Therefore, mosly best to stick to v1.3, and disable the repo in /etc/apt/sources.list.d/pi4j.list

Pi4j v2.0 is next..

VS Code and Raspberry Pi Zero WH

VS Code Remote Development is fantastic, but it doesn't support the Raspberry Pi Zero as the armv6l isn't supported.

However, this it is possible to mount /home/pi as a Samba share and amend files locally, which will perform similarly (for Python development anyway).

This is described here. Install Samba with:

sudo apt install -y samba

Then add the following to /etc/samba/smb.conf as follows:

[PiShare]
 comment=Pi Share
 path=/home/pi
 browseable=yes
 writeable=yes
 only guest=no
 create mask=0740
 directory mask=0750
 public=no

Note that the Samba configuration file can be checked with the testparm command.

Finally, set a password with sudo smbpasswd -a pi. This will create the Samba user pi.

This can be accessed from another computer on the network as \\hostname\share

Raspberry Pi Package Management

APT (Advanced Packaging Tool) is a set of tools that was developed for Debian Linux platform as an easy command line interface for the dpkg utility

apt update
apt upgrade
apt install python3
apt install ./pi4j-1.3.deb # install local package
apt show python3
apt remove python3
apt list # lists all available packages
apt list --installed # lists installed packages
apt list python3 # also shows if package is installed
apt search python3

# list all files contained in the package
dpkg -L python3

# find which package contains a file
dpkg -S /usr/bin/python3

Configuring a Headless RPi

• Install the OS Using the Raspberry Pi Imager.
• Mount the SD card again in the Windows environment
• To enable SSH, create an empty file named 'ssh' in the root of the SD card
• To configure WiFi, create the wpa_supplicant.conf file in the root of the SD card

  ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
  update_config=1
  country=GB
  
  network={
          ssid="ssid"
          psk="psk"
  }
  

• Boot the RPi with the card and run raspi-config to set hostname, interfaces etc.
• Install Java with:

  sudo apt install default-jdk
    
  # or for older RPi mmodels
  sudo apt install openjdk-8-jdk liblog4j2-java wiringpi libmysql-java
  

Edit: turns out these can now be set up with the Raspberry Pi Imager v1.6, which is a lot easier...

Raspberry Pi USB to UART

Instructions on using it can be found here...

Putty is set up as a Serial Connection Type, with the speed set to 115200. The Serial Line can be identified from Device Manager in the ports tab, a the Prolific USB-To-Serial Comm Port.

Note that this doesn't appear to work with Windows 11...

SQL Joins (MySQL)

Rows from two tables can be combined using joins.

Inner Joins

Inner joins return only the rows that meet the specified condition in both tables.

# keyword INNER is optional
SELECT * FROM toys
INNER JOIN bricks
ON toy_id = brick_id;

# Oracle syntax
SELECT * FROM toys, bricks WHERE toy_id = brick_id;

Outer Joins

Outer joins return all the rows from one table, along with the matching rows from the other. Rows without a matching entry in the outer table return null for the outer table's columns.

An outer join can either be left or right, which determines which side of the join the table returns all rows for.

# keyword OUTER is optional
SELECT * FROM toys
LEFT OUTER JOIN bricks
ON toy_id = brick_id;

SELECT * from toys
RIGHT JOIN bricks
ON toy_id = brick_id;

Full Joins

A full join includes unmatched rows from both tables. This is not supported directly by MariaDB.

SELECT * FROM toys
FULL JOIN bricks
ON toy_id = brick_id;

Cross Joins

A cross join returns every row from the first table matched to every row in the second. This will always return the Cartesian product of the two table's rows: i.e. the number of rows in the first table times the number in the second.

SELECT * FROM toys
CROSS JOIN bricks;

See also here

RPi Auto Reconnect

This should reconnect a Raspberry Pi if it drops from the network due to router issues...

*/5 * * * * /bin/ping -q -c10 192.168.1.254 > /dev/null 2>&1 || (sudo /sbin/ifconfig wlan0 down ;sleep 5 ;sudo /sbin/ifconfig wlan0 up ;/usr/bin/logger wifi on wlan0 restarted via crontab)

Photo Sizes

Canon EOS 40D and EOS 77D are both 4x6...

New Raspberry Pi Set up

First, connect to the pi using the USB to UART cable, following the instructions at Adafruit, and enabling the connection in /boot/config.txt

Then set up wifi following the instructions at raspberrypi.org.

Then change the default password using:

sudo passwd pi

Then enable SSH, and update the hostname using:

sudo raspi-config
# Select Interfacing Options and enable SSH
# Select Network Options and change hostname 

Finally, update the software with:

sudo apt update
sudo apt upgrade