Digital Coin Toss

(click for enlargement)

• When the switch is thrown, one LED lights randomly.
• BAvail is not checked because the bit rate is slow.
• The switch is wired to minimize bounce effects.
• No on/off switch is required because at 21mA, AAA cells will last 3 years, AA's more.

Parallel Port Dongle

(click for enlargement)

• 5V power should be obtained from a source external to the port. Suitable sources are a wire from inside the computer case, an isolated and regulated wall transformer, or 3 Alkaline cells. Some dongles obtain power from unused pins. This may work on some parallel ports, but it violates the port specification, and will likely fail on other machines.
• C code to read random data from the port and write it to a binary file is given in dongle.c. The compiled DOS program is dongle.exe.