The first diagram shows how to interface an µC with an 7 segment display through an MC14513B. This little IC is an binary to BCD decoder and driver, that simplifies the interaction between digital circuits and 7 segment displays. Sure - it is a waste of parts and money, because the Atmega could deal with such a display without such an driver, but it was one of my first µC handicraft works.
Interestingly the driver IC was almost as expensive as the µC itself. ^.^°
The second diagram shows a voltage doubler circuit with AC input and 5V DC output.
I own an crosstrainer that need to be connected via a wall power supply to power the electronics (eddy current brake, LCD display, board computer, pulse measurement, etc).
I found it somehow annoying, that i was driving the piece of sports equipment with muscle power, "wasting" several hundred watts of power to get fit and loose weight and nevertheless needed to power the build in electronics with an external power source...
I wanted to use an old bicycle dynamo.
Unfortunately i found no way to mount the bike dynamo on the cross trainer. So i never used the circuit outside of my workbench.
Some interesting links: