almost a technocrat

Turning off the HDMI output on the Raspberry Pi saves around 10 mA. If your applications does not need the HDMI output, you might as well turn it off to optimize power consumption. Below are the Linux commands to turn it off and on.

Turning off the USB and LAN can save around 200 mA of power. However, it is not possible to turn off individual USB or LAN separately as they are sharing the same I.C. Below are the Linux commands to turn off and on the USB and LAN.

Turning off the power (PWR) LED might save you a few mA but if you don't need it, below are the Linux commands to turn it off and on back again. Additionally, you can also change the Activity (ACT) LED behavior as well.

Turning off the WiFi and Bluetooth will save around 30 mA on the Raspberry Pi 3B+. Below are the commands to turn them off and on.

There are many write-ups about this topic. However, this guide is the best and easiest to set up. All you need to do is to enable SSH by adding a blank file with filename of SSH in the boot partition of the SD card. Then connect a LAN cable from your PC to the Raspberry Pi. Yes, direct LAN cable connection from PC to Raspberry Pi. Use any SSH client software you have and log in to raspberrypi.local Below is the video made by the author. Please leave him/her some token of appreciation. Thank you.

If you are working with Raspberry Pi or any other Linux systems and you want to protect how you set up the board, you can use this method to remove the record of custom packages that you have installed. It will make it harder for people to reverse engineer your setup.  They can still clone your SD card and use it on other RPi boards. For that, you can refer to  How to prevent Raspberry Pi SD card cloning  blog post.

A simple script to prevent Raspberry Pi micro SD card cloning. It uses the CPU serial number as the unique ID for authentication. Use this script during boot up to check if the Raspberry Pi CPU serial number matches with the number hardcoded in the script. If the number does not match, then it will shut down Raspberry Pi.