Author: dmcole | Date: September 4, 2011 | 5 Comments »

This was my last take on a circuit to drive the Sawyer Star, an 8×8 LED array that I have spent more than three years adapting from work from more than a dozen people — before I gave up on the project in Summer 2010.

Sawyer schematic

Sawyer v2 schematic drawn in DipTrace

This schematic is basically the one drawn by Mike Ardai (N1ist) for his Color Stick project. I changed only three major things:

  • He uses surface-mount components; I have changed this to a through-hole board.
  • I’ve added an on-board power supply.
  • Mike’s application requires three TLC5916 constant-current drivers, while in my project only one is needed. But the Star needs the addition of a 74HC595 and UDN2981 to source to the LEDs.

Through-hole vs. SMT: While I’m hoping to get some SMT experience in the coming months, I plan to build the first versions of this thing as through-hole because that’s where my comfort level is. From my readings in the DIY Christmas lights communities, it’s clear I’m not the only one who remains uncomfortable regarding SMT. I may redesign the PCB at some later point as SMT.

Power supply: I’ve been thinking about the power supply for the Sawyer Star for a long time. The originator, David Thorpe, uses a nine-volt battery, which he says runs his stars throughout the holiday season without needing a change; I think that with the RS485 chip and off-board PWM, a battery …

Author: dmcole | Date: | No Comments »

Hmm. Sixteen months. My how time flies when you aren’t posting to a blog.

Life happens and my involvement in designing things that flashed LEDs wavered with my inability to get a working prototype for the Sawyer Star, a 64-LED array/matrix that is to be driven by Arduino. I was more than familiar in a general sense with this Open Source microprocessor platform, based on the ATMega 8 family (168s and 328s of late) and it was clear there was a huge community behind it.

After a few …

Author: dmcole | Date: May 15, 2010 | 2 Comments »

Last July I wrote about using Adobe Illustrator to design the schematics I publish here and why I prefer it (you can read that post here). In recent weeks I’ve come to realize two things: despite a great deal of effort on my part, I can’t really design printed circuit boards with Illustrator, and I had completely missed that I wasn’t drawing schematics; I was drawing wiring diagrams.

Let us address the second point first: I had always wondered why, in a schematics application (such as Eagle), when you placed an integrated circuit, for example, the pins were not displayed in sequence. Pins 12-18 might be, for example, in the upper-left-hand corner, while pins 1, 2, 8 and 11 might be in the lower left-hand corner, with pins 3-7, 9 and 10, might be scattered to what seemed like the wind.

I have lost the actual link, but somewhere recently I read a forum posting where it was patiently explained to we non-electrical engineers, that the pins are grouped by internal logical function rather than arranged physically. Also, many integrated circuits are available in a variety of formats – through-hole and surface mount and sometimes in a variety of surface-mount formats as well, where the pin numbers are not the same.

So, what I have been drawing have been diagrams that make it easier for me to breadboard (or perf-board) circuits. While those are beneficial, rarely can they be used for anything else.

My other major gripe with schematics programs (aside …

Author: dmcole | Date: April 13, 2010 | 3 Comments »

It’s been a few months since I last posted here … I don’t think there are any constant visitors who’ve been bummed out about the lack of activity, but I apologize nonetheless.

Since we last spoke I threw the LED matrix project out to the Do It Yourself Christmas community to see if I could get some others interested and willing to help. I got a couple of bites and have spent the last few months working with them, trying to further my goal of building an LED star that has 60 lamps, three colors and can be driven by DMX-512. You can see the discussions.

The current circuit is based on the Atmel ATTiny2313, two 74HC595 shift registers and a ULN2803 Darlington array to handle sink current (plus an RS485 chip to handle DMX signals and associated resistors and capacitors).

Unfortunately, I haven’t been able to make as much progress as I would have liked. I have a breadboarded circuit that works, but unfortunately, it works backwards. That is, when the DMX application sends a signal to an LED to light, it is dark; when there is a DMX signal but sent to have the LED dark, it lights.

Big brains in the DIYC community haven’t been able to figure this one out, so for now I remain mired in my own ignorance.

That’s all I know right now. Stay tuned for more information.

Author: dmcole | Date: December 30, 2009 | No Comments »

For those of the opinion that I fell off the face of the earth, fear not: I merely got involved in non-electronics, such as dealing with a kitchen remodel and unwell pets.

That said, I also focused a bit in recent months on my Christmas lights show and have documented there a few of the DIY efforts not previously chronicled.

Take a gander at:

Have a happy new year and expect to hear more from the workshop later this winter.

Author: dmcole | Date: July 1, 2009 | 6 Comments »

So, I’m going to use Henne’s transceiver for an LED matrix. You coulda probably guessed, if you’d thought about it for a minute or three.

Henne’s DMX LED matrix schematic (click to download PDF).

Henne’s DMX LED matrix schematic (click to download PDF).

Anyway, I fell back on my – ahem – process: first, draw the circuit in Adobe Illustrator and then build it on a breadboard.

(I have been asked in the past why I use Illustrator and not a regular schematic-drawing application such as Eagle or McCad. My first line of defense is the same as when I’m asked why I use InDesign to make slides rather than use the ubiquitous Microsoft PowerPoint: I use the Adobe Creative Suite on a daily basis and am something of an expert with its components. I can create a schematic [or slideshow] faster with the Adobe product than with anything else. Secondarily, I think I get a much better, graphically pleasing, schematic from Illustrator.)

So, there are some changes in this version of the schematic that aren’t electronically or function-driven: instead of the 10-position DIP switch, I have substituted a 2×10 header. This will save only a few cents (around 50) on the bill of materials, but will save some space on the board as well.

These switches signal to the ATMega8515 the DMX start channel to use. They’re set infrequently …

Author: dmcole | Date: June 29, 2009 | 21 Comments »

If you’ve visited my automated Christmas lights page, the letters DMX won’t be unfamiliar to you. For those too lazy to click, it’s an electronic lighting protocol. Two wire. Used extensively in stage shows. And, in recent months, adopted by the DIY Christmas lighting community.

Henne’s DMX transceiver schematic (click to download PDF).

Henne’s DMX transceiver schematic (click to download PDF).

So, I’m working on an idea (I’ll post more when I get closer to the finish) that I want to add to my Christmas lights show, and it therefore needs to talk DMX. Numerous previous postings here will tell you that would mean I’d need to do this on an Atmel chip. Though there are a lot of DMX projects done on Microchips (PICs), fewer have been done on Atmels. And pretty much everyone who has done DMX on the Atmel has based some or all of their work on that of Hendrik Hölscher.

Fortunately for those monolinguists among us, Hendrik — who goes by “Henne” — writes in both German and English. He’s also moderately active on one of the Christmas lights forums.

My initial plans were to write my own code to get my idea off the ground; a few months(!) of fiddling around and I was never even able to pull off my main effect, no less receiving DMX.

During that fiddling, I ran across a web site in Germany that sold …

Author: dmcole | Date: May 7, 2009 | No Comments »

As can be seen from the dates between postings, I took an awful lot of time with this project – and yet, I never really accomplished my goal, which was to have five LEDs independently fading in and out like a candle, driven by an Atmel ATTiny13.

ATTiny13 drives 5 LEDs; programming/test circuit (click to download PDF)

ATTiny13 drives 5 LEDs; programming/test circuit (click to download PDF)

I spent a lot of time with some code that had been created for a Microchip PIC12F675 but it turned out that it was merely random on-off, not fading the way a flickering candle operates. I then spent some time with a second code set, also for a PIC12F675, that did fade nicely, but which had a problem with brightness that I was never able to rectify (it is a duty-cycle issue, I know; I just don’t know how to fix it).

But that second code set did point me in the direction of how to control individual LEDs while within a loop, using bitwise manipulation.

I decided on Sunday that I had a few hours to work on this project and I wanted it finally finished. While the result is not exactly what I wanted, it will suffice.

What I’ve built is a group of four LEDs that fade in and out in an inverse manner. While LED1 fades in, LED2 fades out and LED1 and LED3 work in synch, as …

Author: dmcole | Date: March 13, 2009 | 2 Comments »

If you’ve visited my web site on backyard railroad illumination, you know about my fixation with creating light that flickers as though it were a fire (either from candle or a fireplace).

Schematic of circuit to fade, flicker single LED (click to download PDF)

Schematic of circuit to fade, flicker single LED (click to download PDF)

The first solution to that problem was to modify LED tea candles — readily available at crafts stores and even Walgreens — so that they would work off of standard 12-volt garden lighting (aka: Malibu lighting).

The dirty little secret of that method is that all the tea candles flicker at the same time. I’m not quite sure why this is so — perhaps the proprietary microcontroller used in those devices is time based and since they all start at the same time, they seem to work in synch? In any event, it does make looking at all the “fires” on my layout pulse at the same time.

So, in the back of my mind, I knew I wanted something besides tea lights to make flickering light on the layout. I kept looking around the net, and in January a reader of the backyard illumination site pointed me to an Instructables that showed a circuit to increase the current that could pass through a tea light, allowing up to four LEDs to be driven in the circuit.

The Instructables …

Author: dmcole | Date: March 7, 2009 | No Comments »

In 2007 I played around with the PICAXE, a microprocessor sold by a non-profit in the United Kingdom that comes loaded with a BASIC-like interpreter (you can read more about it here and here). I built some lighthouse beacons and a railroad crossing light using the device. It had one drawback: I had to write the code and program the chip using, sigh, Windows.

Sample schematic to connect ATMega8 to 6-pin ISP (click to download PDF)

Sample schematic to connect ATMega8 to 6-pin ISP (click to download PDF)

In 2008 I learned a little about Microchip’s PIC series of microprocessors because that was the favored chip by most of the developers in the DIY Christmas lighting world. Though I didn’t actually program PICs, I did learn how to burn HEX code into them using an ADM programmer. These too, had a drawback: you had to write the code and program the chip using, ugh, Windows.

Along the way, though, I heard about the AVR series of chips from Atmel Corp., which had a distinct advantage over PICAXEn and PICs: there was a small community of people who used Macintoshes to make them go. There was a full tool-chain for programming in C (a language I had no experience in) and there were USB devices that allowed for burning the code. Well, hello, sweetheart.

So, somewhere along the line in 2008 I bought myself …