This was a bad week for electronics.  I bricked my Atmega 128 development board, and I also discovered that I had ordered the wrong low pass filter.  The IC was $10, and it was supposed to be a DIP8-easily accessible for development.  Oops.  I accidentally ordered an SOIC chip.

Last night I was in The Secret Laboratory, trying to get something done.  After some very fine soldering, I failed to thaw out my bricked development board.  Next I decided to try building an adapter board for the low pass filter.  I had already created the photo mask, but this would be the first time I tried to use the photo-lithography method of creating a board.

Velum makes a good printing medium (especially if you have a laser printer) because it resists crinkling and warping.  My first three attempts failed to produce useable boards, though.  At 10:30PM I gave up and went upstairs to see what Aimee was doing.  She was sleeping.

Since I've been having a difficult time sleeping lately, I did what any other bored...

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A good friend and I have had a long standing "contest" to see who could build a small robot to navigate a path first.  Now, my cohort could have beaten me to the punch on this any time he wished.  His technical expertise is far beyond my own.  He hasn't, though, and this has been a great opportunity (several years in the making) for me to learn about embedded electronics.  After all this time, I am pleased to announce the completion of a very imperfect path navigating robot.

The tracking algorithm is very simple.  The robot travels forward until it gets close to a barrier, then it "looks" around to find the best direction to turn.  It can choose to turn 45 degrees either direction, however I biased the code for 90 degree turns.  If the 45 is truly the best path, it can be utilized.

The bot appears a bit epileptic.  This is because it has a tendency to track ever so slightly to the left.  Every few clock cycles I have it track back the other direction. 



...

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Last week I received the Circuit Bridge silkscreen kit.  With great anticipation, I ripped into the packaging and proceeded to read absolutely no directions.  Ok, I read some.  The kit was $20 and came with a contact frame for exposing the mesh, instructions, a paint squeegee,  and two small pieces of high resolution material, already pre-sensitized. 

In the picture to the right, you can see the contact frame and the circuit design that I used to expose the mesh.  You might be observing that I was crazy enough to use regular paper instead of a transparency.  You are correct!  Even more surprising...it worked! 

Exposing the mesh was a simple matter of layering the paper, ink side down, on top of the mesh inside the magnetic contact...

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Special thanks to GC for pointing me in the right direction regarding AC motor control using triacs.  Rooting about on the web, I found an excellent Word document describing AC power control using a microcontroller.  Basically, the technique is the same as using PWM using DC motors, except that timing becomes more critical.  Power is turned off when the voltage crosses the origin, for whatever the PWM period is, and is turned back on for the remainder of the cycle.

Ok.  This was my second attempt.  Along the way, I discovered that printing on a color printer is a bad idea.  Why?  High end color laser printers put a waxy coating on top of their toner to protect the stuff they print out.  Now, reverse that coating when ironing on to a circuit board you can imagine that the protective coating prevents the toner from transferring to the board.  And, it makes it a pain in the ass to clean the board afterwards.

You may notice that this board isn't quite as pretty.  It looks like someone might have hand drawn some of the traces...Here is the thing, electronic circuits like big, round, fat traces (they make the rockin' world go round)! ...

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I just tried hooking both servos up to my prototype board, to no avail.  I had already been concerned about power problems, which is what prompted the design of the printed board.  Unfortunately, I made some serious errors on the board and will need to modify the plans.  Namely, the pads need to be larger, and I printed the circuit on the wrong side of the board (it was mirrored).  I'm not real pleased with the toner transfer method of printing boards, although I will try it again before I drop it altogether.  Next I'll try the screen printing method already noted, and after that I intend to try direct printing on the board.

On the plus side of things, I had suspected power and\or noise would become and issue for me-and it did!  Since I'm in a small holding pattern with printed PCBs, this will give me a chance to mod my original prototype and work through these issues.

I've been working on some AVR circuits lately, and of course I've run into some limitations with my prototype board.  Namely, it's enormous, and I prefer to work from a CAD design (thanks Eagle).  In order to shrink my design I decided to try the toner transfer PCB method.  It goes like this:

Print mirrored circuit design on transfer paper Prepare copper clad board (scuff and degrease) Iron toner sheet onto board Soak in water to remove paper This is a step I added-bake the board in the oven at 400 degrees for 10 minutes.  My initial attempts had problems with the toner lifting from the board. Touch up the traces with a marker\paint Etch After trying this out, I can tell you...it is not easy or free of frustration.  It is cheap, though, and it would be great for prototyping surface mount boards.  My board is a through-hole board...so I still have lots of drilling to do.  A more promising method might be to use high resolution screen printing to get the resist onto the board.  This way, one screen...

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My name is Gary Holbrook, and you can view my resume at www.garyholbrook.com, or you can email me at gholbrook at digitalintuition dot com.  By day I am a C# developer.  By evening, I like to work on electronics projects.  Since my background is in programming, I am naturally drawn to microcontrollers.  Atmel is my manufacturer of choice because I like the price of the Winavr suite of tools.

I build my own circuit boards from scratch, using a photo transfer process and ferric chloride etchant.  This is all part of my philosophy on electronics, which (in summary) dictates that the best electronics projects are the least expensive!