In the 80’s microprocessors had become mainstream and my curiosity moved from analog hardware solutions to digital ones. There were several local stores that I could buy 7400 series Integrated Circuits in DIP packages for pennies. I was fascinated with the ease of building an If/Then digital circuit and tie that to a discrete component to power the action desired. Darlington transistors, especially PNP ones were terribly easy to interface with an open collector Integrated circuit. When the Zilog Z80 Microprocessor came out, I moved onto writing machine code into EEPROMS to get the desired results into my If/Then digital circuits I already knew. (I built a firmware based recipe box and a homemade Inverter/Charger that is commonly called a UPS today.)