Larson Scanner project introduction

Okay, it’s time to make a realistic Larson Scanner. You may know it as a Cylon Eye from Battlestar Gallactica or the lights on the front of KITT, the car in Knight Rider. It’s a popular project because it looks cool, but I’ve seen (and built) a ton of lousy imitations. What makes the original so interesting is that the bright tracking light leaves a fading tale behind it. That’s a bit more work to implement, but I’m up for the challenge. Update: check out the complete project.

After the break I embedded a video of the Larson Scanner from Knight Rider. You can pause it to get an idea of what’s going on here. The brightest light is always on the leading edge, the rest fade with time.

So my implementation will happen in a couple of stages:

  • Write some code to drive a PWM signal on the pins of an AVR microcontroller
  • Write some code to automatically fade an LED once the focus has left it
  • Write some code to change where the focus is on a row of LEDs
This is just an introduction so check back soon! Continue reading

Light bulb microcontroller salvaged with HVSP

The ATtiny13 microcontroller from that LED light bulb is now waiting for new firmware. I used High Voltage Serial Programming to erase the chip, which clears the lock bits. I then reset the high fuse back to 0xFF. It was 0xFA before which disables the reset pin (and enables brownout detection) making In System Programming impossible.

I finished mapping out the PCB and it does use the example circuit from the buck converter's datasheet. Looks like it was outputting 12V and using a 7V zener diode to step down to the 5V source the tiny13 needed. I'm going to depopulate the PSU and patch in a 12V feed for further testing. I'm thinking my first project will be a red/green flasher for a Christmas porch light.

LED lightbulb schematic

I had a bit of time to test out the PCB from that LED light bulb. I've just been using continuity tester and ohm-meter for this. Here's the LED logic. High-side transistors but I haven't quite figured out how the resistors are wired. I've also established the A/C side of the switching regulator but I'm having trouble figuring out the output. Similar to the example in the datasheet but not quite the same.

Porting AVR code for MSP430 chips

I’ve just finished my first port of code from AVR over to MSP430. I used the garage door code button source because it’s fresh on my mind and I can reproduce the hardware on the TI Launchpad board. This provided a few sets of challenges, and showed me what I can do from the start to make my code more portable. I’ll get into both of those subjects and share the ported code after the break. Continue reading