My nephew recently made an inquiry as to the possibility of creating a low cost non contact digital tachometer.  With my typical over-optimism, I nearly shrieked "No problem!  Piece of Cake!".  This didn't turn out to be entirely true, but the demonstration project I put together was pretty straight forward. The first thing I needed was an optical sensor.  Obviously ambient light can be a problem, so I wanted something tuned to infrared.  As fortune would have it, someone had the brilliant idea of putting an infrared emitter (LED) and a detector (a phototransistor) in the same case!  The sensor I ended up using is an Omron EE-SF5. For...

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It was pointless to even glance around before unleashing a rivulet of colorful language.  Nobody was near enough to hear my complaint.  Fortunately.  Another chip had been bricked by my careless use of PonyProg, and unlike the two recent DIP Atmega168s...this one was an Atmega128, mounted in my favorite development board from Olimex.  The madness had to end.  For the third time I had reset a chip to use its low speed internal oscillator, making it too slow for ICSP access.  These micro controllers are so small, they don't even make good paperweights.

It was time to buy a better programmer.  Something USB based that I could use directly from AVR studio.  After finding the AVR Dragon, I thought my problems were solved.  The Dragon does ICSP, JTAG, DebugWire, and Parallel\High Voltage programming.  All for $50.  What else could I possibly need?

Well...ICSP wires would have been nice.  As it turns out, the Dragon is the barest of the bare.  After several attempts to get the finicky Dragon to program...

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A while ago I bought the MG Chemicals budget etchant kit.  The kit comes with a sparging unit, five liter tank, and air pump.  It was about $30, which sounded reasonable at the time.  Having tried using the tank a couple of times, I'm not smitten.  The board holder would probably work really well for a 9" board...but since I work with small, simple circuits...the holder (integrated into the sparging unit) is worthless.  I ended up drilling holes in my board to hang the board from.

That brings me to the sparging unit.  This thing is supposed to circulate the etchant in the tank, and around the board by bubbling air into the tank.  Right.  First, the tubing is really stiff (think fish tank tubing), so the sparging unit never wants to sit straight.  Also...all the air came out of only one end of the unit, so the distribution was not uniform.  Could I have fixed this?  Maybe...except the thing is submerged in a vat of acid.

Alright.  I was pretty irritated when my boards didn't turn out well, so I went...

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Recently I wrote about my first experience with surface mount technology.  As part of that ongoing project, I needed a capable chip mounted on a development board.  That chip turned out to be an Atmega169 TQFP, which I will clock at 16Mhz.  To date, I'm still working only on single sided boards.  This would be my most ambitious project yet.

Like the last board that I made, I printed this one with a lithographic process.  The mask was printed on velum and then transferred to the positive sensitized board using a fluorescent lamp.



  Velum actually works surprisingly well.  It doesn't warp when printed, and holds toner quite well.  Even though this board is very basic, you can see that the routing is quite...

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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.