This Star with LEDs is one of my current hobby projects based on the Motorola 68HC908JL3. As of December 1999 I have received the finished boards and the Star is working beautifully! I hope to put a photograph of the finished unit on this page soon. There are 40 LED's around the border of the Star, each of which can be controlled individually with variable brightness. Two trim-pots attached to two of the JL3's ADC channels allow analogue control of the pattern being displayed.
The current firmware was written in a couple of hours in the middle of the night and as such it is in something of a mess, but it works. There is a simple programming language for programming the LED patterns. Currently the program is stored in the JL3's FLASH but later I want to write code to utilise the Star's serial EEPROM for program storage and the RS232 interface for downloading new programs from a PC.
There is a 7-pin header for programming the HC08 and debugging with the P&E software. To use this you need my HC08PGMR board or something similar to act as an interface between a PC serial port and the Star's 7-pin header.
The Star is just a hobby project and I did not spend much time to make it perfect. But so far (the EEPROM and MAX232 circuits are untested) it seems to be working very well.
There are resistors in series with each LED. To obtain maximum brightness I have used 0-ohms (wire links) in these locations. The JL3 seems to handle it ok (LED's are driven with a 1/5th duty cycle). The power consumption is about 40 milliamps for the pattern supplied in the current firmware (not many LEDs on at once). If you are not implementing a pattern with many LEDs on at once, the 7805 can be replaced with a more convenient 78L05.
The current firmware is not very good and not even all of the instructions have been tested. But it does work at least in some degree, with the default program showing a nice LED-chasing effect with gradual brightness and speed controlled with the right-hand trim pot. When I get time I will tidy up the firmware and implement some more instructions to make more complex patterns possible.
For programming, the switches on the HC08PGMR board should be ON-OFF-ON-ON.
Do you want to make your own Star? Here are all the files you need. The files are also available via the HC08 FTP archive . These files are available free for personal use (non-profit). If you make money out of the Star then I want some of the profit too :-)
Here is a diagram of the board as seen in the EAGLE PCB layout software (the current version of the board is slightly different).