Since the object oriented "revolution", abstraction and code reuse are the bywords of modern software development even when programming in non-OO languages. But use of these techniques has lagged in highly embedded development due to perceived inefficiencies compared to C and assembler. Yet embedded development can be incredibly detail-oriented and time consuming. It took a bug report discussion and listserv conversation (you can read the originals by following the links, or just read my summary after the break) between a couple of highly experienced engineers to figure out the best solution for an 8 line chunk of code that on the surface is quite simple. It just enables the SPI bus.
This experience shows the power of FOSS and abstraction in microcosm. First, judging by the discussion, any one of these engineers (including myself) working alone would likely not have figured out the best solution. This would have meant revisiting the issue some time in the future. And second, once this time-consuming, detail-oriented problem was solved it never needs to be solved again. This (added to countless similar cases) creates tremendous efficiencies affecting (judging by hits to this blog) engineers across the entire world. Neither of these effects would have taken place in classic closed-source development.
Tuesday, June 5, 2012
Wednesday, May 30, 2012
TLC5940, TLC5941 and Arduino
The TI TLC59xx chip family are constant current LED drivers that have some pretty impressive stats. I'm experimenting with the TLC5941 which has 16 constant current channels, 80mA sink capability per channel, 17v maximum LED voltage and 4096 PWM intensity levels per channel. If you want to use it, here's an Eagle schematic and footprint to get you going: https://github.com/gandrewstone/tlc594x/blob/master/eagle/tlc594X.lbr
And here's a photo of 2 quad chip driver boards that I made.
Packing those features into such a small chip has created a device that has got some nasty traps that are not described in the datasheet (or hard to understand) and so it is easy for beginning hardware hackers to either fry a couple of chips or just give up in frustration. If you are looking into using this chip, check out my experiences after the break.
And here's a photo of 2 quad chip driver boards that I made.
Packing those features into such a small chip has created a device that has got some nasty traps that are not described in the datasheet (or hard to understand) and so it is easy for beginning hardware hackers to either fry a couple of chips or just give up in frustration. If you are looking into using this chip, check out my experiences after the break.
Friday, May 4, 2012
If you wish to make an apple pie from scratch you must first invent the universe
I recently googled this Carl Sagan quote using the search "if you wish to make an apple pie from scratch meaning" and was pretty dismayed that the top result not only misquotes him but comes from a yahoo Q&A site with the following "best" answer:
"Sagan was merely saying all the elements of an apple pie made from scratch [reduced to the lowest common denominator] are elemental to the universe and the universe had to be there before an apple pie could be made from them.
Hardly profound, though it's often quoted."
This result probably says more about the mental acuity of the analyzer then about what is being analyzed. Unfortunately answers are "closed" so nothing can be done about the yahoo page. So I shall give it a shot here and if you like my response please link/forward/facebook/google+ this posting so we can collectively knock Yahoo off of the top spot! So let me start over:
Quote
"If you wish to make an apple pie from scratch you must first invent the universe" Carl Sagan
You can hear a clip of him saying it straight here: http://www.youtube.com/watch?v=7s664NsLeFM, but you'll probably by a lot more entertained by this remix Symphony of Science: A Glorious Dawn
Literal Meaning
Just so we are all on the same page, the simplest level of interpretation is that the baker's fundamental ingredients are not fundamental at all. Apple trees produced the apples, wheat plants produced the flour in the crust, sugar cane produces the sugar. And of course this idea must be recursively applied. What made the chemicals and matter that these plants used? The big bang and stars made them out of more fundamental particles and energy. What made the energy the plants used to arrange the matter?
This is essentially as far as the original "answer" goes, But this is a trivial analysis.
Let's take a Bite out of this Pie
A great way to analyze a quote is to first make your analysis, and then modify the original quote with a different one that matches your analysis. Then compare the two and see what the original has that's missing from the new one & what the new one has that's missing from the original. So here's what Sagan might have said if he was as smart as the author of the "best" answer:
1. God made the universe, you just rearrange it.
Here I am clearly differing by introducing "God" into the quote. Its possible that Sagan's personal beliefs precluded this formulation (I don't know or care). But the important point is that the omission of "God" in his quote aims it directly at humanity, at us.
So let's leave God out of the quote:
2. You can't make stuff from scratch because you're always using other stuff that's already been made.
This formulation in the negative is limiting -- but is that what Sagan wanted to say? That you CANT make an apple pie from scratch? His formulation is in fact enabling; "if you wish to make...". He believes that someday we will truly make a pie from scratch and is seeking to define what that means. By formulating the sentence positively, the quote is infused with the hope and promise of humanity's potential.
So let's reformulate in the positive, but tweak the noun:
3. If you wish to make a particle accelerator from scratch you must first invent the universe
Who is the "you" in this quote? By choosing something as prosaic, as domestic as an apple pie he implies that the makers shall someday be, well, anybody and the making shall be an everyday occurrence. By choosing "particle accelerator" I pretty clearly point this at a small esoteric subgroup. He is also saying that the most common of thing are actually made up of complex ideas.
4. (and finally the misquotation) If you wish to make an apple pie from scratch you must first create the universe.
What's the difference between "creation" and "invention"? Well, a potter can "create" a clay pot (for example) by throwing clay on a wheel. But how can she "invent" one? She really cannot; its already been invented. But she can invent a new kind of pot. With the term "invent" Sagan is clearly suggesting not the mechanical act of creation but the mental act of invention. It is not enough for us to create the pie from fundamental particles; to truly make it "from scratch" we must invent (and therefore understand) the entire mathematical/informatic/computational underpinnings of the universe that either must have been before the first particle existed or that was forced to be by that particle's existence.
Actually, I'm still struggling with what he meant by invent. Since the universe already exists it cannot really be invented again. Was he suggesting the actual invention and subsequent creation of new universes by humankind? Or was he implying that inventing the universe would allow the controlled creation of space and matter within our existing framework? ...quantum mechanics predicts that particles and antiparticles are spontaneously created all the time...
Regardless, in this one sentence Sagan has left us with a large, tasty slice of his hopes and dreams for the future of science and humanity!
"Sagan was merely saying all the elements of an apple pie made from scratch [reduced to the lowest common denominator] are elemental to the universe and the universe had to be there before an apple pie could be made from them.
Hardly profound, though it's often quoted."
This result probably says more about the mental acuity of the analyzer then about what is being analyzed. Unfortunately answers are "closed" so nothing can be done about the yahoo page. So I shall give it a shot here and if you like my response please link/forward/facebook/google+ this posting so we can collectively knock Yahoo off of the top spot! So let me start over:
Quote
"If you wish to make an apple pie from scratch you must first invent the universe" Carl Sagan
You can hear a clip of him saying it straight here: http://www.youtube.com/watch?v=7s664NsLeFM, but you'll probably by a lot more entertained by this remix Symphony of Science: A Glorious Dawn
Literal Meaning
Just so we are all on the same page, the simplest level of interpretation is that the baker's fundamental ingredients are not fundamental at all. Apple trees produced the apples, wheat plants produced the flour in the crust, sugar cane produces the sugar. And of course this idea must be recursively applied. What made the chemicals and matter that these plants used? The big bang and stars made them out of more fundamental particles and energy. What made the energy the plants used to arrange the matter?
This is essentially as far as the original "answer" goes, But this is a trivial analysis.
Let's take a Bite out of this Pie
A great way to analyze a quote is to first make your analysis, and then modify the original quote with a different one that matches your analysis. Then compare the two and see what the original has that's missing from the new one & what the new one has that's missing from the original. So here's what Sagan might have said if he was as smart as the author of the "best" answer:
1. God made the universe, you just rearrange it.
Here I am clearly differing by introducing "God" into the quote. Its possible that Sagan's personal beliefs precluded this formulation (I don't know or care). But the important point is that the omission of "God" in his quote aims it directly at humanity, at us.
So let's leave God out of the quote:
2. You can't make stuff from scratch because you're always using other stuff that's already been made.
This formulation in the negative is limiting -- but is that what Sagan wanted to say? That you CANT make an apple pie from scratch? His formulation is in fact enabling; "if you wish to make...". He believes that someday we will truly make a pie from scratch and is seeking to define what that means. By formulating the sentence positively, the quote is infused with the hope and promise of humanity's potential.
So let's reformulate in the positive, but tweak the noun:
3. If you wish to make a particle accelerator from scratch you must first invent the universe
Who is the "you" in this quote? By choosing something as prosaic, as domestic as an apple pie he implies that the makers shall someday be, well, anybody and the making shall be an everyday occurrence. By choosing "particle accelerator" I pretty clearly point this at a small esoteric subgroup. He is also saying that the most common of thing are actually made up of complex ideas.
4. (and finally the misquotation) If you wish to make an apple pie from scratch you must first create the universe.
What's the difference between "creation" and "invention"? Well, a potter can "create" a clay pot (for example) by throwing clay on a wheel. But how can she "invent" one? She really cannot; its already been invented. But she can invent a new kind of pot. With the term "invent" Sagan is clearly suggesting not the mechanical act of creation but the mental act of invention. It is not enough for us to create the pie from fundamental particles; to truly make it "from scratch" we must invent (and therefore understand) the entire mathematical/informatic/computational underpinnings of the universe that either must have been before the first particle existed or that was forced to be by that particle's existence.
Actually, I'm still struggling with what he meant by invent. Since the universe already exists it cannot really be invented again. Was he suggesting the actual invention and subsequent creation of new universes by humankind? Or was he implying that inventing the universe would allow the controlled creation of space and matter within our existing framework? ...quantum mechanics predicts that particles and antiparticles are spontaneously created all the time...
Regardless, in this one sentence Sagan has left us with a large, tasty slice of his hopes and dreams for the future of science and humanity!
Friday, February 10, 2012
AVRez: A Simple Arduino API for other chips
The Arduino IS its software library. As I'm sure you've seen on the web, its pretty easy to breadboard an Arduino -- and to do it for about 10 bucks -- so Arduino is not really about the hardware. And the IDE is no Eclipse or Emacs. While this may actually be an advantage for complete beginners :-) it cannot be the IDE that sustains the Arduino's popularity.
The true secret to the Arduino is in its software library -- which AFAIK actually came from a project called Wiring. Here's a quick quiz to prove my point. What does this do:
Huh??? 99.9% of you will say (for .1% who get it right and don't get my drift, your next challenge is to write the equivalent of analogRead(11) without looking at the datasheet).
Well if you happen to have read the Atmel 328 processor spec, and pored through the avr-gcc io328xxx.h header file you'd know that this sets the bit corresponding to PB2 in the data direction register to high.
Make sense yet? No? Let me make it clearer.
pinMode(10, OUTPUT);
That's the Arduino/Wiring library version of the same code above. And pretty much anyone who understands that pins must be designated input or output can understand that line. You don't even have to be familiar with the Arduino/Wiring library! Its the magic of self-documenting code.
So when you go digging around in "AppNotes" and other example code, don't be fooled by the garbage you find. Its not "real" embedded programmers that directly use unreadable archana like "ADMUX |= 1; ASCSRA |= _BV(ADSC); while (ADSCRA&_BV(ADSC); result=ADCL | (((uint16_t)(ADCH))*256);" (that's how you read an analog pin PB2 by the way). Its actually just the "real bad" ones :-). Or institutions who have a vested interested in locking you into their platform.
In fact the only real confusion with "pinMode(10,OUTPUT)" is identifying what "10" means.
This is why I've decided to make a super simple library that I call "AVRez" that provides a similar API for other chips. You can look at it at here. This library is intended for use with chips that are not "Arduino" compatible so a few changes had to be made made, most especially in the pin out. However the basic API is instantly understandable to anyone whether they know the Arduino APIs or not.
With this library, for example, you can call "pinMode(pinB2, OUTPUT);". The only visual difference between this and the Arduino library is the constant "pinB2". Instead of making up separate names and numbers for each pin, I've chosen to use the pin names exactly as described in the datasheet. This will make code running on "barebones" processors more understandable.
Often performance is cited as the reason registers are directly bit-banged in "main" code. But this argument is better understood as simply a criticism of existing abstraction layers -- just because one abstraction layer is inefficient does not mean all must be!
In AVRez, for performance reasons a pin name actually expands to a complete list of all registers that are needed to manipulate the pin. Then the macros "pinMode", "digitialWrite", etc just use the registers that they needs and the rest get dropped by the C preprocessor. This allows the AVRez functions to be quite efficient; for example "pinMode" ultimately becomes just "DDRB |= _BV(PB2);" which is about the most efficient "C" implementation possible (but actually, technically not quite correct. It should be "cli(); DDRB |= _BV(PB2); sei();". Can you figure out why? In fact this issue is actually why the AVR processor has 2 special commands just for the job that are named "sbr" and "cbr". Compare this to the implementations you see in the Arduino core library...
But one issue with this approach is that the name "pinB2" does not have a type. So you can't store it into a variable like this:
int pin = pinB2;
But it would be quite possible to add a pin enumeration to the library and therefore fall back to something a bit less efficient. Then you could use something like:
int pin = pinIndex(pinB2); // Or maybe "= pinB2index;" is clearer...
pinMode(pin, OUTPUT);
One question for thought before I sign off: what is the MOST efficient way to translate a pin enumeration into code? What we see in the Arduino library ain't it! :-)
The true secret to the Arduino is in its software library -- which AFAIK actually came from a project called Wiring. Here's a quick quiz to prove my point. What does this do:
Huh??? 99.9% of you will say (for .1% who get it right and don't get my drift, your next challenge is to write the equivalent of analogRead(11) without looking at the datasheet).
Well if you happen to have read the Atmel 328 processor spec, and pored through the avr-gcc io328xxx.h header file you'd know that this sets the bit corresponding to PB2 in the data direction register to high.
Make sense yet? No? Let me make it clearer.
pinMode(10, OUTPUT);
That's the Arduino/Wiring library version of the same code above. And pretty much anyone who understands that pins must be designated input or output can understand that line. You don't even have to be familiar with the Arduino/Wiring library! Its the magic of self-documenting code.
So when you go digging around in "AppNotes" and other example code, don't be fooled by the garbage you find. Its not "real" embedded programmers that directly use unreadable archana like "ADMUX |= 1; ASCSRA |= _BV(ADSC); while (ADSCRA&_BV(ADSC); result=ADCL | (((uint16_t)(ADCH))*256);" (that's how you read an analog pin PB2 by the way). Its actually just the "real bad" ones :-). Or institutions who have a vested interested in locking you into their platform.
In fact the only real confusion with "pinMode(10,OUTPUT)" is identifying what "10" means.
This is why I've decided to make a super simple library that I call "AVRez" that provides a similar API for other chips. You can look at it at here. This library is intended for use with chips that are not "Arduino" compatible so a few changes had to be made made, most especially in the pin out. However the basic API is instantly understandable to anyone whether they know the Arduino APIs or not.
With this library, for example, you can call "pinMode(pinB2, OUTPUT);". The only visual difference between this and the Arduino library is the constant "pinB2". Instead of making up separate names and numbers for each pin, I've chosen to use the pin names exactly as described in the datasheet. This will make code running on "barebones" processors more understandable.
Often performance is cited as the reason registers are directly bit-banged in "main" code. But this argument is better understood as simply a criticism of existing abstraction layers -- just because one abstraction layer is inefficient does not mean all must be!
In AVRez, for performance reasons a pin name actually expands to a complete list of all registers that are needed to manipulate the pin. Then the macros "pinMode", "digitialWrite", etc just use the registers that they needs and the rest get dropped by the C preprocessor. This allows the AVRez functions to be quite efficient; for example "pinMode" ultimately becomes just "DDRB |= _BV(PB2);" which is about the most efficient "C" implementation possible (but actually, technically not quite correct. It should be "cli(); DDRB |= _BV(PB2); sei();". Can you figure out why? In fact this issue is actually why the AVR processor has 2 special commands just for the job that are named "sbr" and "cbr". Compare this to the implementations you see in the Arduino core library...
But one issue with this approach is that the name "pinB2" does not have a type. So you can't store it into a variable like this:
int pin = pinB2;
But it would be quite possible to add a pin enumeration to the library and therefore fall back to something a bit less efficient. Then you could use something like:
int pin = pinIndex(pinB2); // Or maybe "= pinB2index;" is clearer...
pinMode(pin, OUTPUT);
One question for thought before I sign off: what is the MOST efficient way to translate a pin enumeration into code? What we see in the Arduino library ain't it! :-)
Tuesday, January 31, 2012
Ubuntu 11.10/Gnome 3.0: Surviving the transition!
I've had significant issues with the new Ubuntu GUI and Gnome 3.0; ranging from irritations (difficulty to create launchers) to bugs (mouse stops responding). If you are googling around I'm sure you've seen the near universal cry of dismay. If there is one message to send Canonical (if any of you ever read this posting) it would be that while its a great idea to "dumb down" the interface so a single GUI will work between your desktop and touch machines, you can't disable the advantages available through a mouse interface!
Anyway, here is what I did to make it workable. These are mostly culled from various web sources; they are not my original work.
Friday, January 27, 2012
Transdescending Arduino: Going cheap and small
The Arduino is great; a microController you can actually do something with for 30 bucks! Ok, but your train layout needs 5 of them ($150), your home sensor network needs 10 + $40 xbee cards (clocking in at $700!). Or the mere fact that your want to KEEP your projects around means that you get nailed for 30 bucks over and over again.
But wait a second... the AVR328p is a 3 dollar chip! And the AVR ATMega48 (pin compatible but with a LOT less space) is 2 bucks (for 10)! And if your requirements are extremely minimal, there's the ATTINY13 which comes in as little as 60 cents -- but in an inconvenient package (you'll be better off spending another 4 dimes and getting one for 1 buck).
Let's hack up a bunch of these chips so next project we'll have lots of choices...
Note: If you've figured out the hardware part and just need some software help check out this posting: AVRez -- "arduino" style APIs for other chips
But wait a second... the AVR328p is a 3 dollar chip! And the AVR ATMega48 (pin compatible but with a LOT less space) is 2 bucks (for 10)! And if your requirements are extremely minimal, there's the ATTINY13 which comes in as little as 60 cents -- but in an inconvenient package (you'll be better off spending another 4 dimes and getting one for 1 buck).
Let's hack up a bunch of these chips so next project we'll have lots of choices...
Note: If you've figured out the hardware part and just need some software help check out this posting: AVRez -- "arduino" style APIs for other chips
Friday, January 20, 2012
DIY PCB SMT Breakout board fabrication: Results
In the last posting I described how I made a few PCBs to act as SMT breakouts. I've discovered that this seems to be a pretty ideal job for DIY PCB work! To mount thru-hole stuff, you need the hole -- and that means hand drilling... but a small breakout board can be done on a single side, and its possible to use .1" Right Angle headers soldered onto an oval thru-hole pad so you don't even need to drill the hole for the breakout header.
In my last posting I finished with the circuit board ironed onto the blank PCB. It turns out that the final steps are quite easy. First you get some etchant. I used ferric chloride from Radio Shack, but I wish I had used muriatic acid and hydrogen peroxide as it seems slightly better for the environment. I poured the etchant in a leftover food container (now forever dedicated to PCB etching) and left the boards in for about 30 minutes. I used a twisted wire hanger to keep my fingers out of the etchant:
Then rinse the board in lots of water, and leave the tap running to dilute any drips of etchant solution that go down your drain. When you're done, put the top on the container (make sure it seals!) and store for next time.
To remove the laser printer toner, I tried a few paint removers, liquid sanders, etc. Nothing really worked. It turns out that Acetone (nail polish remover) is required. Its available in the paint section of hardware stores, and is absolutely amazing at the job. 2 swipes with a rag daubed in Acetone cleans the toner like wiping milk off a table!
Next I soldered the parts on to the PCBs using a toaster oven. I was concerned that the lack of a solder mask might make the solder bridge across PCB pads because its impossible to keep the solder paste onto pads. In fact, I don't even bother, I just paint a thin line down across all the pads in a row (see my earlier post on DIY SMT soldering techniques here). But in fact, the solder balled up nicely as you can see here:
These are tiny SOIC-8 and SOT-23/5 parts. I left the chip off the rightmost SOT-23/5 to see how well the solder wicked onto the pads. Before putting it in the oven, the space between all the pads was completely covered with solder paste -- the wicking works great!
I cut some of these boards with a hobbiest bandsaw, like you can get for $200 at Home Depot. But its even easier to cut them by scoring the front an back with a ruler and then breaking them against the edge of table (preferably metal). Place something hard (like a metal or hardwood block) on top, grab the protruding board with pliers and then crack it by rotating the pliers downwards quickly.
One surprise was how fine a pitch may be possible. I had originally "designed" this board for professional fabrication and I accidentally left some tiny lettering on the board. Amazingly, it transferred to the PCB perfectly well! Here is a close up:
As you can see, by the ballpoint pen I put in for scale, the height of these letters is less then one millimeter! I will need to go back to the file to check, but I'll bet that the line width is just a few mils (thousandths of an inch) wide. Many professional PCB houses won't do less then 8mils! Of course, they require repeatability across hundreds of large boards -- my goal is to get a single small breakout board out of a panel with a half dozen attempts.
So basically, if the transfer works without smudging or distortion you can get amazingly fine detail. And from my limited experience it does tend to do so reliably across portions of the board that can be 2 square inches in size. This makes me believe that it may be possible to home fabricate chip-scale BGA breakout boards -- at least for small BGA packages. I have not discovered anyone who has tried it yet; so I think that will be my next experiment (as soon as I find a "fun" BGA chip)!
EDIT: Here's a photo of the SOIC8 installed on a PCB. I think that its better to put all the pins in a single row, rather then the DIP configuration because that gives you the other side of the breakout board to use to make your circuit!
Also note that no drilling is needed! Get right angle breakaway headers and then solder them to the (undrilled) thru hole pad.
EDIT 2: Here is a photo of a SOT-363 chip with a 2 mil circle indicating pin 1. To get an idea of the size, the circle is indicated by the lead of a standard 1/4 watt resistor. As you can see the 2 mil line width was etched perfectly!
In my last posting I finished with the circuit board ironed onto the blank PCB. It turns out that the final steps are quite easy. First you get some etchant. I used ferric chloride from Radio Shack, but I wish I had used muriatic acid and hydrogen peroxide as it seems slightly better for the environment. I poured the etchant in a leftover food container (now forever dedicated to PCB etching) and left the boards in for about 30 minutes. I used a twisted wire hanger to keep my fingers out of the etchant:
Then rinse the board in lots of water, and leave the tap running to dilute any drips of etchant solution that go down your drain. When you're done, put the top on the container (make sure it seals!) and store for next time.
To remove the laser printer toner, I tried a few paint removers, liquid sanders, etc. Nothing really worked. It turns out that Acetone (nail polish remover) is required. Its available in the paint section of hardware stores, and is absolutely amazing at the job. 2 swipes with a rag daubed in Acetone cleans the toner like wiping milk off a table!
Next I soldered the parts on to the PCBs using a toaster oven. I was concerned that the lack of a solder mask might make the solder bridge across PCB pads because its impossible to keep the solder paste onto pads. In fact, I don't even bother, I just paint a thin line down across all the pads in a row (see my earlier post on DIY SMT soldering techniques here). But in fact, the solder balled up nicely as you can see here:
These are tiny SOIC-8 and SOT-23/5 parts. I left the chip off the rightmost SOT-23/5 to see how well the solder wicked onto the pads. Before putting it in the oven, the space between all the pads was completely covered with solder paste -- the wicking works great!
I cut some of these boards with a hobbiest bandsaw, like you can get for $200 at Home Depot. But its even easier to cut them by scoring the front an back with a ruler and then breaking them against the edge of table (preferably metal). Place something hard (like a metal or hardwood block) on top, grab the protruding board with pliers and then crack it by rotating the pliers downwards quickly.
One surprise was how fine a pitch may be possible. I had originally "designed" this board for professional fabrication and I accidentally left some tiny lettering on the board. Amazingly, it transferred to the PCB perfectly well! Here is a close up:
As you can see, by the ballpoint pen I put in for scale, the height of these letters is less then one millimeter! I will need to go back to the file to check, but I'll bet that the line width is just a few mils (thousandths of an inch) wide. Many professional PCB houses won't do less then 8mils! Of course, they require repeatability across hundreds of large boards -- my goal is to get a single small breakout board out of a panel with a half dozen attempts.
So basically, if the transfer works without smudging or distortion you can get amazingly fine detail. And from my limited experience it does tend to do so reliably across portions of the board that can be 2 square inches in size. This makes me believe that it may be possible to home fabricate chip-scale BGA breakout boards -- at least for small BGA packages. I have not discovered anyone who has tried it yet; so I think that will be my next experiment (as soon as I find a "fun" BGA chip)!
EDIT: Here's a photo of the SOIC8 installed on a PCB. I think that its better to put all the pins in a single row, rather then the DIP configuration because that gives you the other side of the breakout board to use to make your circuit!
Also note that no drilling is needed! Get right angle breakaway headers and then solder them to the (undrilled) thru hole pad.
EDIT 2: Here is a photo of a SOT-363 chip with a 2 mil circle indicating pin 1. To get an idea of the size, the circle is indicated by the lead of a standard 1/4 watt resistor. As you can see the 2 mil line width was etched perfectly!
Friday, January 13, 2012
DIY PCB fabrication; Breakout Board Toner Transfer Experiments
Using modern components in PCB circuit board design essentially requires the use of small surface mount packages. Testing these components can be costly and time consuming if you need to have a break-out-board professionally fabricated for every component. It is possible to hand-solder extremely thin magnet wire to individual leads of a SMT package but that is a very painstaking process.
It would be much easier if individual PCBs could be hand-fabricated for the task. I dug around on the web and DIY PCB fabrication for very small parts seems quite tricky; most people use home PCBs to make larger circuits out of thru-hole parts.
However, even if multi-chip SMT designs are not feasible, it would be very valuable to be able to rapidly fabricate single chip breakout boards for SMT parts (for noobies: a breakout board is a PCB that simply brings all the pins in a SMT chip to a male header that can be plugged into a solderless breadboard). Especially small parts; if you are putting a TQFP-144 on you board there are places where you can buy breakouts. And there are fewer footprints so you could build up a "library" of breakouts. But there are tons of different packages for components ranging from 2 to 32 pins!
Making these small-pin count PCBs might be feasible (where large SMT designs are not) for several reasons. First, the PCB will be quite small, allowing you to panel multiples "tries" onto a single DIY board. You only need one success! Second, the routing will be pretty short and simple. If the pins are placed on either side of the chip the routes will be short and on a single side (so you can try the same circuit on both sides!). Finally, I think that right angle .1" headers could be used in place of straight pins, so the final board would not need to be drilled. This will save a lot of time (and painstaking work).
Here are my first attempts (ever) to use the toner transfer method to put a mask on copper PCBs. I panelized 6 SOIC-8 and 6 SOT-23/5 breakout boards onto a space about 2x3 inches:
And the back side attempts:
The basic methodology (for people who are reading this as an instructable) is to:
1. Remove all layers of your PCB except routes, pads and vias. Export it as an image (monochrome, 600 dpi). Load it up in a graphics editor (gimp), reverse the color, and horizontally mirror it.
2. Next, use a laser printer to print it onto some kind of paper. You want a paper with unique, generally undesirable properties; essentially the toner should just barely stick and it should dissolve readily in water. Four types are commonly suggested:
A) glossy paper ripped from a cheap magazine/catalog
B) glossy photo paper
C) sticker backing paper (pull the stickers off and print on the shiny side)
D) speciality PCB toner transfer paper.
3. "clean" a blank PCB with steel wool, and then iron the toner on by placing the iron at its highest setting on the paper (which is on the PCB) for about a minute. You can't move the paper relative to the PCB so some masking tape on the corners might help. Also don't push down hard, and don't move the iron around much.
4. Soak the PCB in water for about 5 minutes and then rub the paper off. You can rub quite hard; if it toner comes off then it did not transfer.
The PCB on the upper left of image 1 was made with glossy photo paper. This paper essentially did not work for me; it would glue itself to the iron and then separate from the PCB or pick it up as well. The toner was still melted at this point so most of it stayed with the paper.
The upper right image 1 board shows what happens when you push down too hard. Pressure on the melted toner caused it to spread out. So don't do that!! :-) The bottom left of image 1 was ironed on for several minutes. It got so hot it changed the copper color -- additionally the paper was extremely hard to remove. Oops! The last photo on image 1 was again done with glossy photo paper. The paper still lifted off with the iron but amazingly it left a perfect transfer in the middle! Unfortunately I doubt its repeatable.
I left board on photo 2 clean to show how the PCB should look after it has been rubbed by the steel wool. The other 3 boards on the bottom image show transfers with the sticker-backing paper with ironing times of 30seconds, 1 minute, and 1:30. I'm sure you can see which is which since they show more toner sticking. In fact, the last image has perfect transfers of 9 out of the 12 circuits! The only miss transfers are on the top of the PCB. Clearly I did not get that portion hot enough (in fact, I think that it may have been under the steam holes of the iron). Removal of the paper was pretty quick under hot water; about 5 minutes (so clearly the boards were not under the iron for too long). But the paper did not "pill" up like other web postings suggest; it mostly peeled off. After ironing, the paper it was a little browned in spots but not significantly.
Like any other craft there is clearly a bit of skill and practice required. And some experimentation is required to become familiar with your particular tools. However, so far this looks like a pretty feasible method for breakout board fabrication. In the next installment I will attempt to etch the boards and solder the parts on!
It would be much easier if individual PCBs could be hand-fabricated for the task. I dug around on the web and DIY PCB fabrication for very small parts seems quite tricky; most people use home PCBs to make larger circuits out of thru-hole parts.
However, even if multi-chip SMT designs are not feasible, it would be very valuable to be able to rapidly fabricate single chip breakout boards for SMT parts (for noobies: a breakout board is a PCB that simply brings all the pins in a SMT chip to a male header that can be plugged into a solderless breadboard). Especially small parts; if you are putting a TQFP-144 on you board there are places where you can buy breakouts. And there are fewer footprints so you could build up a "library" of breakouts. But there are tons of different packages for components ranging from 2 to 32 pins!
Making these small-pin count PCBs might be feasible (where large SMT designs are not) for several reasons. First, the PCB will be quite small, allowing you to panel multiples "tries" onto a single DIY board. You only need one success! Second, the routing will be pretty short and simple. If the pins are placed on either side of the chip the routes will be short and on a single side (so you can try the same circuit on both sides!). Finally, I think that right angle .1" headers could be used in place of straight pins, so the final board would not need to be drilled. This will save a lot of time (and painstaking work).
Here are my first attempts (ever) to use the toner transfer method to put a mask on copper PCBs. I panelized 6 SOIC-8 and 6 SOT-23/5 breakout boards onto a space about 2x3 inches:
And the back side attempts:
The basic methodology (for people who are reading this as an instructable) is to:
1. Remove all layers of your PCB except routes, pads and vias. Export it as an image (monochrome, 600 dpi). Load it up in a graphics editor (gimp), reverse the color, and horizontally mirror it.
2. Next, use a laser printer to print it onto some kind of paper. You want a paper with unique, generally undesirable properties; essentially the toner should just barely stick and it should dissolve readily in water. Four types are commonly suggested:
A) glossy paper ripped from a cheap magazine/catalog
B) glossy photo paper
C) sticker backing paper (pull the stickers off and print on the shiny side)
D) speciality PCB toner transfer paper.
3. "clean" a blank PCB with steel wool, and then iron the toner on by placing the iron at its highest setting on the paper (which is on the PCB) for about a minute. You can't move the paper relative to the PCB so some masking tape on the corners might help. Also don't push down hard, and don't move the iron around much.
4. Soak the PCB in water for about 5 minutes and then rub the paper off. You can rub quite hard; if it toner comes off then it did not transfer.
The PCB on the upper left of image 1 was made with glossy photo paper. This paper essentially did not work for me; it would glue itself to the iron and then separate from the PCB or pick it up as well. The toner was still melted at this point so most of it stayed with the paper.
The upper right image 1 board shows what happens when you push down too hard. Pressure on the melted toner caused it to spread out. So don't do that!! :-) The bottom left of image 1 was ironed on for several minutes. It got so hot it changed the copper color -- additionally the paper was extremely hard to remove. Oops! The last photo on image 1 was again done with glossy photo paper. The paper still lifted off with the iron but amazingly it left a perfect transfer in the middle! Unfortunately I doubt its repeatable.
I left board on photo 2 clean to show how the PCB should look after it has been rubbed by the steel wool. The other 3 boards on the bottom image show transfers with the sticker-backing paper with ironing times of 30seconds, 1 minute, and 1:30. I'm sure you can see which is which since they show more toner sticking. In fact, the last image has perfect transfers of 9 out of the 12 circuits! The only miss transfers are on the top of the PCB. Clearly I did not get that portion hot enough (in fact, I think that it may have been under the steam holes of the iron). Removal of the paper was pretty quick under hot water; about 5 minutes (so clearly the boards were not under the iron for too long). But the paper did not "pill" up like other web postings suggest; it mostly peeled off. After ironing, the paper it was a little browned in spots but not significantly.
Like any other craft there is clearly a bit of skill and practice required. And some experimentation is required to become familiar with your particular tools. However, so far this looks like a pretty feasible method for breakout board fabrication. In the next installment I will attempt to etch the boards and solder the parts on!
Tuesday, January 10, 2012
Ubuntu 11.10 64bit CadSoft Eagle 6.0.0 installation pain
I think Eagle 6 was rushed to market :-). It resists installation on the most popular Linux distros, and when you do finally get it working it pops up with an "I'm sorry, there's a nasty bug" dialog. But Kudos to Cadsoft for admitting it!!!
Here are my notes on the installation. I think I might be missing a step or two so if you follow these and run into issues, please post a comment!!!
These instructions should also mostly work in 32 bit Linux distros, but you won't need to install as much (remove the packages with "i386", or "32" in their names).
Step 1: Prep Ubuntu for 32 bit compilation
Next, get and install libpng14 from source:
http://sourceforge.net/projects/libpng/files/libpng14/1.4.8/libpng-1.4.8.tar.xz/download
32 bit distros should remove "CFLAGS=-m32" and just use this line instead:
./configure --prefix=/
[Troubleshooting] If you get the error: "configure: error: C compiler cannot create executables" check the config.log file. If the problem is: "/usr/bin/ld: cannot find crt1.o: No such file or directory" then you did not install g++-multilib gcc-multilib.
If you get: "configure: error: zlib not installed" you did not install lib32z1-dev
Now install Eagle:
chmod a+x eagle-lin*
sudo ./eagle-lin*
Good Luck and keep building OSHW!!!
Here are my notes on the installation. I think I might be missing a step or two so if you follow these and run into issues, please post a comment!!!
These instructions should also mostly work in 32 bit Linux distros, but you won't need to install as much (remove the packages with "i386", or "32" in their names).
Step 1: Prep Ubuntu for 32 bit compilation
sudo apt-get install build-essential lib32z1-dev g++-multilib gcc-multilib ia32-libs libssl1.0.0 libssl1.0.0:i386 libjpeg8 libjpeg8:i386
Next, get and install libpng14 from source:
http://sourceforge.net/projects/libpng/files/libpng14/1.4.8/libpng-1.4.8.tar.xz/download
tar xvf libpng-1.4.8* cd libpng-* ./configure CFLAGS=-m32 --prefix=/ make check sudo make install
32 bit distros should remove "CFLAGS=-m32" and just use this line instead:
./configure --prefix=/
[Troubleshooting] If you get the error: "configure: error: C compiler cannot create executables" check the config.log file. If the problem is: "/usr/bin/ld: cannot find crt1.o: No such file or directory" then you did not install g++-multilib gcc-multilib.
If you get: "configure: error: zlib not installed" you did not install lib32z1-dev
Now install Eagle:
chmod a+x eagle-lin*
sudo ./eagle-lin*
Good Luck and keep building OSHW!!!
Wednesday, November 2, 2011
Open Hardware Journal
Bruce Perens (who did Busybox and Debian as well as defining "Open Source") has created an Open Hardware Journal (http://openhardware.org/journal/). Check out the first issue, I've got two articles in it! Ok ok, probably he needed more submissions which is why my stuff made the cut :-). But hey I'll take it!
The first article "An Open Hardware Platform for USB Firmware Updates and
General USB Development" is about the USB interface on the Lightuino. I chose that topic because this interface is a cheap and tiny way to put USB in many of your projects. The interface will talk SPI to your uP or some SPI chip, or I2C (although I did not use that in the Lightuino). And it will do serial (USB CDC ACM if you need the formal acronym) or emulate an input device (USB HID). Read the article for more info, and check out my code on github here: https://github.com/gandrewstone/toastedCypressUsb
My second article "A Return To Open Devices" is about my ideas around the philosophy and driving forces behind the open hardware movement. I'm sure the people who come to open hardware do it for many different reasons; this is simply my perspective.
The first article "An Open Hardware Platform for USB Firmware Updates and
General USB Development" is about the USB interface on the Lightuino. I chose that topic because this interface is a cheap and tiny way to put USB in many of your projects. The interface will talk SPI to your uP or some SPI chip, or I2C (although I did not use that in the Lightuino). And it will do serial (USB CDC ACM if you need the formal acronym) or emulate an input device (USB HID). Read the article for more info, and check out my code on github here: https://github.com/gandrewstone/toastedCypressUsb
My second article "A Return To Open Devices" is about my ideas around the philosophy and driving forces behind the open hardware movement. I'm sure the people who come to open hardware do it for many different reasons; this is simply my perspective.
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