Archive for August, 2009


RS-485 speed test rig


I just got started on a project all of the sudden that pretty much begins and ends at the speed I can squeeze out of various pieces of wire via RS-485.  To find out, I rigged up 2 Atmega48’s each with SN75176 RS-485 transceivers.  I happened to have those lying around (ok, stuck to various boards) because they ‘re what I use for DMX-512…

I had to start out by coercing a software UART into working, since the hardware UART is needed for the actual test channel.  The current challenge is to get the driver and repeater code to behave in the right sequence so I can actually start doing bulk testing at higher bit rates.  The obnoxious part is having to move around the AVR-ISP header.  My logic helper will fix that problem eventually, as I can just run 2 of the 8 ports to the AVRs, another couple as software-UART readout so I can watch both debug ports at once, and voila.

RS485 test


Toner-transfer prototype PCBs


There was a post today on Hackaday about using a dowel to help transfer toner as part of an etching process.  It reminded me about something my fiancee found, actually…  She was googling my name for pictures, and ran across images of a PCB I did during the development process of a product that’s now into its 3rd production run (granted, only 25 units per run, but it is part of a $10,000 tool…).  It just so happens though that these images are on PulsarFX’s website, used as the showcase project for the toner transfer paper and method they sell.  Pretty slick, eh?

So I was thinking, I should probably try to thoroughly document how I actually pulled off such a PCB.  I’ll start sketching out how I’m going to organize it, and hopefully get started writing it up sometime soon.  It may be text-only for now, as I’m not really in a position to do a whole picture sequence at the moment.  Getting married in 3 weeks is not the time to start trying to re-assemble my PCB pipeline…


First-generation LED project


I first built LED lighting hardware around 3 years ago, after first reading about the BAM technique from Artistic License.  I ended up building a kit from scratch consisting of a controller and 8 fixtures.  The controller has 2 boards with ATmega8515’s each driving 16x 2N2222’s grouped in 4’s, with RJ-45 connectors.  The fixtures are 4x4x2″ enclosures with PCBs holding a total of 96 LEDs each, 24 each of red, green, blue, and white, again with RJ-45’s.  The first round of 4 fixtures were strictly resistive-ballast, while the second round used LM317’s in constant-current mode.  This coupled with a slightly higher drive voltage allows the fixtures to be strung on anywhere from 3ft to 100ft of standard Ethernet cable.

Last Christmas I decided to go a little overboard on the first tree of my own…  4 of the fixtures are embedded in the tree, while 4 more are behind the curtains as uplights.  Control is via DMX-512 driven by an ENTTEC Open-DMX USB bridge, with a cable running to my computer running custom color-changing code written in Python.

2008 Christmas tree


My workspace


Here’s a shot of my workspace, just to the left of my desktop:


On the breadboard you’ve got an ATmega168 at the bottom for LED driver development, with space for an FT232R board, which is chilling on the row above.  Above that is the ATmega32 that took over its role because I can hook up the AVR Dragon (left) in JTAG mode so I could actually debug what was breaking…

Above that is the EDTP “Frame Thrower” ENC28J60 board, and Olimex’s PIC18F67J60 module with an ICSP adapter hanging off it.  At the far right is a rotating LED base I bought at the “Pirate Store” in the mall, disassembled for, um, upgrades.  At the top left is a stack of boards including an early PIC ICD2, and a Xilinx Spartan-3E dev board.


Getting started


I figured it’s time for me to start up a blog, as that’s going to be the easiest way of getting my projects visible to the world…  We’ll see how well it goes, eh?

At the moment I’m working on three main projects:

  • Multichannel LED driver capable of 3-85 channels depending on chip/package, with up to 16-bit resolution and crazy-fast refresh rates
  • “Logic helper” based on the FT4232 that acts like the inverse of the BusPirate, controlling up to 8 ports of 2-6 IO’s each, supporting common serial protocols as well as custom interfaces like AVR-ISP, etc.
  • Inexpensive Ethernet module with a somewhat innovative means of developing applications

They’re all at various stages of development, and it’ll be a bit of a race to see which is “ready” first, since especially the last two depend on each other to a fair degree.  Even testing of the LED chip “requires” the logic helper…

I plan on starting to post some development thoughts, pictures, and status on this blog… we’ll see if anybody cares ;-)