Over the weekend I found some time to solder together a kit that I'd picked up before getting stuck into the Arduino. It's the mini-scrolling LED sign kit from Hansen Hobbies and seems to be the only non-RC kit they make. It's a really nice kit that's fun to put together and at $40 it's not too expensive.
The finished kit produces an 24x8 red-LED display, using three 8x8 LED matrices. The LEDs are driven from the PIC16F628A microcontroller through three 74AC164 shift registers and eight PN2222A NPN transistors, with the transistors switching power to the rows of the matrices and the shift registers controlling the columns. The kit comes with comprehensive instructions and explanations of the circuit operation. Nicely done overall.
Here are some photos of the build process (click the image for a larger version):
1) The kit contents (I'd already started soldering when I realized I'd forgotten to take the initial photo)
2) Finished with passive components. One of the resistors broke so I substituted one I had lying around - can you guess which one? :-)
3) Finished with everything except the LED matrices. The components are packed in tight and the solder pads are very small - making for a few tricky soldering moments.
4) Everything in place. The LED matrices required some jiggling to get in - quite a few tiny movements to the pins with needle-nose pliers to get them to slot into the tiny through-holes. The PCB is very well put together with the shift register ICs on the underside from everything else to save space.
Everything worked on the first test! The four micro-tact switches control the editing of the message (all ASCII characters are there) and the message scrolling speed (8 speeds from stopped to blur). You can also connect the board up to a PC using RS232 or directly to another microcontroller - pretty neat.
The PIC is programmed with a 'well done' message that displays until you put in your own. Below is a video of the first one I entered (click to play).
Next up - using transistors with the Arduino to multiplex LED 10-bar arrays - eventually working up to designing and building my own scrolling sign using the Arduino, and beyond!