1. • WiringPi 2.52 - WiringPi
     Gordon doesn't mention it on his blog, but it's probably best to remove  the pre-installed WiringPi software package before  installing version 2.52.  As mentioned in his blog though, version 2.52 is required for Raspberry Pi 4B:

** Note:  MD5 checksum provided is for version 2.52.  

$ sudo apt remove wiringpi                                      

$ wget https://project-downloads.drogon.net/wiringpi-latest.deb 

$ md5sum wiringpi-latest.deb                                    

6fa89970f6e9e1590127d10bb0800c1b  wiringpi-latest.deb           

$ sudo dpkg -i wiringpi-latest.deb                              

1. • Log4Pi:  Logging Utility

   • PCA9685:  Servo Driver

   • PCA9635:  LED/Motor Driver

   • MCP23017:  Extended GPIO

   • ADS1115: Analogue to Digital 

   • LCD1602: LCD Display via pcf8574

   • Link to all schematics: [click here]