AVR Freaks

When you did this, did you use a microcontroller, or a bunch of switches and pushbuttons?  If a microcontroller, why not simply write a small program?

I built a retro clock with the 7219 and a Mega88 and it worked great.  The SPI engine in the AVR is perfectly suited for this type of thing.

JIm

TO each his own then......

All the best on your quest.

JIm

I do sort of see the charm of doing this by hand with a bunch of switches on a breadboard.

Unfortunately in this way you amplify human flaws (silly mistakes, forgetfullness) and in the end you have to start all over again.

Are you afraid of using a uC?

Libraries for chips such as (for example) max7219 do not appear out of nothing, nor are they written in a single typing session.

They often start very similar to what you do with your manual switches, but the switches are flipped by software and a uC instead of fingers.

You could begin for example by writing some very simple functions, which just flip a single output bit, and add a delay of a few us, just to make sure you have no problems with timing.In the next operation you change a few things in the order you think the switches should be flipped, and try again with the new sequence.

On each iteration you can verifie the result with an oscilloscope / logic analyser and compare it with the datasheet.

And then if you've got some sensible response out of your hardware for the first time, you are very happy.

After that follow a few iterations of cleaning up and extending the software library you've just written.

The first single character written (and visible) on a HD44780 I did in this way.

Timing was very conservative, probably 10x or more slower than was stated in the datasheet.

When that worked, I wrote some loops to iterate over a string and send a whole sentence to the display.

In the meantime the code gets reviewed multiple times, timing gets improved, horrible stuff gets rewritten, commended out code gets removed etc.

After you've gone through this process you have a thorough understanding of how to write to your hardware, and you have also a library to use in your projects for this hardware.

While doing this, also write some comments about the errors you've made, how you corrected them and why you did use particular software constructs to solve your problems.

When source code is properly written, and thus also readable by human beings, it is easy to read from the source code how things are done.

Repeating in comments what is being done is a mostly silly excersise, but I see it happening all the time.

Commenting why things are done in a particular way is much more usefull.

Write the comments as how you would explain things to someone who has never seen your code before and has no clue of what it is, what pieces it consists of, nor how those pieces fit together.

Start with explaining the big picture.

If you've gone through this process and have a nicely written and cleaned up library you can put it on github or your own site or share it with others.

When you have been using your library for some time (months or years), you'll forget more and more details, but that's ok.

You're just changing from a library writer to a user for this particular library.

It might even be usefull to yourself if you've changed some of the comments to be compatible with doxygen, so you can extract some html as a user manual for your library.