So I built a pretty good prototype of my LED matrix, AVR-based toy (as you can see in my previous post, as well as this video). Now I’ve decided to get a PCB made, using mostly surface mount components, which will make it nice and compact. You can see to the right a 3D render of approximately what it will look like, right now a company in Bulgaria is fabricating my PCB, hopefully I’ll get it within another week or two.

Whether or not it actually will work once I get it & assemble it, remains to be seen.

I used cadsoft’s Eagle tool to design the PCB, and I used this plugin along with povray in order to create the 3d render. Also I sort of edited in the image of the LED matrix…since they didn’t already have a 3d part built for it. But it looks reasonable enough I think.

I’ve had a little time to come back to working on my AVR ATMega-based project. First of all, I replaced a bunch of free wires with a ribbon cable, which makes things a lot easier to handle. I’ve also wired up the buttons, so now I can write little programs which can be controlled by user input. Right now you can just move the dot around and change its color, next I think I will make a 1 or 2 player pong game.

Download a short video of it in action (~700KB), or view it here:
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I have a prototype of the hardware side of my Nintendo DS-based heart rate monitor. I’m using the awesome DSerial to interface an IR LED & IR phototransistor to the DS.

It works ok, but the signal is not strong enough. Slight movements can make the data unusable. I think I need to work on either amplifying the signal, or increasing the sensitivity of the DSerial. Also I need to rig up some velcro to stick the sensor to your finger, so you don’t have to hold it in place.

Here you can see my “sensor”:

Here is the connection to the DS:

And finally, here is a screenshot of the DS’s lower screen, which is just graphing the data coming from the DSerial’s ADC:

Check out this movie of it in action: dserial_heart_monitor.avi (1.5MB)

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)