A neat-looking device for DS homebrew development is natrium42’s DSerial. The features include

• 8051 microcontroller running at 24MHz
• Reprogrammable from DS, premade firmwares available
• Free development tools available
• 18 GPIO lines, 2 status LEDs
• UART with RS-232 level converter (can be disabled)
• Full-speed USB 2.0 device (does not support USB host)
• PWM and ADC available
• 2D tilt sensor

I’m hoping to make some cool stuff with it…my first plan is to build a portable heart monitor, that can also tell you how stressed-out you are, based on your ‘coherence’ (essentially you take the FFT of your heart rate over time, and you want most of the energy to fall near to 0.1Hz)

Here I am posting the schematic of the current design, and my proposed schematic for design revision 2. The main changes are:

• Directly drive the ROW inputs with transistors, instead of using shift register. I have enough I/O pins that there is no need for a shift register here, and the transistors will allow a decent amount of current through.
• Limit the current coming out of the COLUMNS with resistors. This is needed now that there will be more current flowing through. Before I got away without them, probably because each row was being driven by a single output pin of the shift registers
• Use shift registers on columns as before, but this time with a latch, so you wont see the data being shifted in. Thus the ‘off’ LEDs will really be off, instead of the faint flicker/glow

Schematic Rev. 1 (What I currently have built)

Schematic Rev. 2 (What I am planning to change next time)

I ported the code to C. Now it is easier for me to work with.

This makes it easy to scale things, so now I have 10 boucing lights instead of one:

bounce3.mpg - 3MB

I’m no ASM master, so I could probably be doing it the hard way, but this code in ASM:

(more…)

I finally got the code worked out for bouncing a little ball around. Here’s a short movie:

bounce.avi - 200KB
MPG1 format - 1.1MB
I think next, I am going to rewrite all this code in C. The ASM is getting too complex for me to manage efficiently, I spend too much time tracking down ASM bugs versus actually writing code.

I hardcoded this pattern to load into SRAM on bootup: