Arduino "talking" to other device over serial link

The code is working. The tutorial... latter parts... needs work. But at...

... you will find an essay about an Arduino with an LED and a "doorbell" switch (momentary, connecting to ground. Input pulled up with Arudino's BRILLIANT internal pull ups).

The Arduino is connected, serial link, separate from the "programming" link to a PC. In that PC, an app running which can send messages which will turn the Arudino's LED on or off, and the app in the PC repeatedly consults the Arudino and reports, on the PCs screen, the state of the "doorbell".

Now... "what's it good for"? Not much, with LED and switch. But the work paves the way for all sorts of Fun Stuff.

A challenge you might find fun is given in the essay: Can you replace the PC described in the essay, the "master" device, and replace it with a second Arduino, doing what the PC does? "Rule" of the game: The "first" Arduino has to remain exactly as it is in the essay.

The task set in the challenge shouldn't be hard to accomplish, but I think you could have fun with it.

Something else which might amuse readers: Have a go at replacing the Delphi program I used to drive the PC side of things? A little harder than the first challenge, but maybe useful to less experienced Arduino fans?

I hope you enjoy what's in the essay.

Apologies to anyone who was unable to download the source-code for the PC. The link-checker was down, and my browser was making a good guess at where to find things.

The link is now repaired.

Hoping someone will take up the challenge in the tutorial: Replacing the PC side of the master/slave system. How about it, Linux types? Shouldn't be hard, and the Arduino side has been done for you. You do need to be able to write to/ read from your PC's serial port. Just pointing a PC running Hyperterminal or PuTTY at the Arduino "works", but misses the point of the exercise.

Enjoy.... ?