标签: microcontrollers

Much like Douglas Adams' fictional detective Dirk Gently, I'm a great believer in "the fundamental interconnectedness of all things" and how one thing so often leads to another.   Several days ago, for example, I received a bunch of emails requesting consideration for a free GPAK4 development board. The problem was that I'd written about it yonks ago.   So I asked one of the guys what had led him to that article, and he responded that he'd seen a reference to it on the DangerousPrototypes.com website. Well, this sounded like an intriguing destination, so I immediately bounced over there to take a look, and the first thing I saw was something called the DigiRule.     This little beauty was created by a guy called Brad. You can find out more about Brad and his creations at BradsProjects.com . In a nutshell, the DigiRule is a 6-inch (15 cm) ruler whose divisions are marked in binary rather than decimal.   On the rear of the ruler we find useful information like logic gate and flip flop truth tables, a binary conversion chart, a few select SMD component footprints, and some hole sizes. On the front -- as you can see in this video -- we find a bunch of buttons and LEDs and digital functions like primitive logic gates, different types of register elements, and a 4-bit binary up/down counter (all of these functions are actually implemented using one of Microchip Technology's PIC18F43K20 microcontrollers).   As I've said before on many occasions: "Show me a flashing LED and I'll show you a man drooling!" I want one. Brad isn’t selling them. I'm going to have to build my own. Even better, maybe I can persuade my chum Duane Benson to build some for us, because (a) he can whip out a new board design much faster than yours truly and (b) his designs usually work first time.   But if we're going to build our own, then you can bet we're going to add a few features of our own. For example, we could make the little rascal Arduino/chipKIT compatible and provide it with a USB port so folks can hack it if they wish (we'd make this an open source design, of course).   I do like the simple logic functions and registers on Brad's ruler, but -- in the case of the simple logic gates, for example -- he uses only one color of LED. Thus, in the case of the AND, function, the LED representing the output is only on (logic 1) if both of the inputs are on (logic 1). I'd prefer to use bi-colored LEDs, where green represents logic 0 and red represents logic 1, for example.   What else could we add? How about a real-time clock capability, possibly with a small OLED display to present the time? (I think we're going to need to use a rechargeable battery.) Maybe connection points for two flying lead probes and a piezoelectric sounder so we could use it as a continuity tester -- perhaps even a simple multimeter...   What say you? If you were going to do this, what would you include on the little scamp? Any suggestions will be gratefully received, but you'd better throw them into the mix quickly.

Ever-innovative Microchip has a couple of new families of 8 bit microcontrollers. The CPUs remain about the same as in the rest of the PIC16 family, but the peripherals offer some pretty interesting capabilities.   I find the company’s part numbers baffling and can no longer correlate feature sets to numeric designations without a cheat sheet. The latest PIC16F18877 family comprises quite a few variants with different memory sizes.   As an old embedded guy, I’m always fascinated by the boundary where digital hardware, firmware and analog intersect. In the early days of micros it was really hard to read analog signals. There were no monolithic A/D converters; you had to buy an epoxy-potted module to sample signals, and 12 bits was about the max resolution that was possible. These things cost hundreds of dollars back when inflation hadn’t hollowed out the greenback. Long defunct companies (like Analogic and Burr-Brown) made these, as well as some still with us (e.g., Analog Devices). Conversion speeds were typically in the tens of microseconds.   The following picture shows a typical 12 bit unit dating from the mid-70s. The MAS-1202 retailed for $270, or about $1100 in today’s dollars, and was an enormous 4 by 2 inches:   How things have changed! Can you imagine paying a kilobuck for an ADC of, by today’s standards, fairly uninspiring performance?   (Potted modules of all sorts were really common, especially for analog components with tough specs. Around 1973 I went overseas for a month to support our products. We used a 40J potted op amp from Analog Devices, which had a very high failure rate. I replaced a sickening number. Finally done, I left Japan to head home and was assigned seat number 40J. Of course, it was broken.)   Microchip’s new family has, as is typical with modern MCUs, an ADC on board. But this one is very different from that 1970s device, and is also unlike any 2015 A/D I’m familiar with. A couple of features stand out.   First, the ADC can do math on the sampled signal – with no intervention from the CPU! In fact, the processor can be asleep while the A/D reads and analyzes data. This is nice from a power-reduction standpoint, of course, but it also means that while the processor is awake it can manage other activities while the analog subsystem churns through data.   Math operations are controlled by a blizzard of registers and there are more modes than I care to describe here. But to paint a picture, the part can accumulate a specified number of values, right shifting each new result by any number of bits, average a number of samples (and, yes, a division is done without CPU intervention), or low-pass filter the signal.   But wait – there’s more.   After these operations the result can be differenced from the previous reading (a sort of first derivative), against a programmed setpoint, against a filtered value, etc.   And more: that result can create an interrupt based on a number of conditions, like it being outside of a set of thresholds, or between them, or a bunch of other, similar, conditions. All while the CPU tends to other matters or is off in dreamland.   It gets even better. Conversions can be initiated by one of about 30 different conditions. For instance, if a timer overflows, or by an external pin being asserted. Or the output of either of two analog comparators.   Conversions can also start when very complex external events occur. The signal measurement timer, a 24 bit counter that measures things like external pulse widths, frequencies and duty cycles, or even the time difference between two signals, can start acquisition.   Maybe you need a really exotic start-of-conversion, something no vendor would supply since your needs are unique. These MCUs, like some of other parts from Microchip, contain four identical configurable logic cells (CLC). These are poor-person’s FPGAs (they refer to them using the amusing phrase “puddle of gates” rather than the lofty “sea of gates” term used by FPGA vendors) that are completely programmable. Any CLC can trigger the ADC. Each CLC looks like this: The PIC16F18877’s ADC is only 10 bits. But outside of that it’s a hugely programmable and capable device. It would be fun to have a few beers with some developers to brainstorm some cool applications for it.   In quantity parts are a bit over a buck. A large number of packages are available, including prototyping-friendly DIP as well as an assortment of SMT. There’s more info here , but, alas, as of this writing no datasheet has been published. The information in this article comes from a pre-release datasheet Microchip provided. I’m told the spec documents will be out shortly.

Keeping a record of the design progress, measured results, decisions made, and calculations performed are all part of the job description for any engineer. There are many aspects to any project, and for a project involving microcontrollers and/or programmable logic, this is compounded by programs that are compiled down to object code. The reasons we need to keep the records include (but are not limited to):   Prove that the design works Obtain data for use in data sheets Determine approaches for testing the unit Patents Legal liability Accounting auditing (for tax credits or progress payments) ISO auditing. My current approach is very 20 th Century -- being completely paper driven. I have a 3-ring binder in which I keep requirements, data sheets, listings, schematics, sundry pieces of paper like POs as well as a notebook. In truth the notebook is more of a scrapbook. It contains hand written notes, drawings and calculations along with clippings pasted in like Excel worksheets, photos, ‘scope plots, design reviews and other details. It is all very clumsy and especially stressful when trying to follow a trail during an ISO audit.   The app I want would replicate the design binder (with improvements) as a single file. I imagine it would have to be distributed across a PC as well as a tablet. Of course it would start with the ability to enter text on a keyboard and have the ability to include MSWord and pdf files. It would be possible to add handwritten notes, preferably with a stylus since it works better than my finger for writing. Converting the handwritten text to machine readable format would be a plus when searching for something. The app would have the ability to add notation to the included pdf sheets. It would need a simple spreadsheet since I sometimes gather data at an environmental chamber away from my desk and then execute some simple calculations. But it would also need to be able to integrate more complex calculations from Excel or even Matlab although I would settle for screen shots with hyperlinks to the respective files.   I would like to see a feature to add bookmarks so that there could be cross linkages throughout the file. Cross linkages into source code would really be nice, since some data cannot be included in the source files.   Interfacing to instrumentation like DVMs or ‘scopes through USB or Wi-Fi is probably unrealistic in the short term, although if there was a script or programming language it could be customized.   Obviously there would be a central folder location where all the electronic files reside but synchronization should be as transparent as possible.   There are dozens of apps that address some aspects of my wish list, but so far I haven’t found any that allows any really cohesive approach. We have the technology, and I hope this blog nudges someone to produce this ultimate app. Sometimes I feel that a laptop may answer my hardware requirements and the Windows environment comes closest to the level of integration that I need, but the handwritten input is important and the clam-shell format is often inconvenient. The AceCAD Digimemo L2  also has potential as an input device, allowing the full pen and paper experience, but the approach lacks some of the other features I would like.   How do you document your projects? Do you know of any app that approaches my needs?   Aubrey Kagan

Max's recent blog ( I've been a naughty engineer ) sent me rummaging through my own notebooks for something I wrote a while back:    Keeping a record of the design progress, measured results, decisions made, and calculations performed are all part of the job description for any engineer. There are many aspects to any project, and for a project involving microcontrollers and/or programmable logic, this is compounded by programs that are compiled down to object code. The reasons we need to keep the records include (but are not limited to):   Prove that the design works Obtain data for use in data sheets Determine approaches for testing the unit Patents Legal liability Accounting auditing (for tax credits or progress payments) ISO auditing. My current approach is very 20 th Century -- being completely paper driven. I have a 3-ring binder in which I keep requirements, data sheets, listings, schematics, sundry pieces of paper like POs as well as a notebook. In truth the notebook is more of a scrapbook. It contains hand written notes, drawings and calculations along with clippings pasted in like Excel worksheets, photos, ‘scope plots, design reviews and other details. It is all very clumsy and especially stressful when trying to follow a trail during an ISO audit.   The app I want would replicate the design binder (with improvements) as a single file. I imagine it would have to be distributed across a PC as well as a tablet. Of course it would start with the ability to enter text on a keyboard and have the ability to include MSWord and pdf files. It would be possible to add handwritten notes, preferably with a stylus since it works better than my finger for writing. Converting the handwritten text to machine readable format would be a plus when searching for something. The app would have the ability to add notation to the included pdf sheets. It would need a simple spreadsheet since I sometimes gather data at an environmental chamber away from my desk and then execute some simple calculations. But it would also need to be able to integrate more complex calculations from Excel or even Matlab although I would settle for screen shots with hyperlinks to the respective files.   I would like to see a feature to add bookmarks so that there could be cross linkages throughout the file. Cross linkages into source code would really be nice, since some data cannot be included in the source files.   Interfacing to instrumentation like DVMs or ‘scopes through USB or Wi-Fi is probably unrealistic in the short term, although if there was a script or programming language it could be customized.   Obviously there would be a central folder location where all the electronic files reside but synchronization should be as transparent as possible.   There are dozens of apps that address some aspects of my wish list, but so far I haven’t found any that allows any really cohesive approach. We have the technology, and I hope this blog nudges someone to produce this ultimate app. Sometimes I feel that a laptop may answer my hardware requirements and the Windows environment comes closest to the level of integration that I need, but the handwritten input is important and the clam-shell format is often inconvenient. The AceCAD Digimemo L2  also has potential as an input device, allowing the full pen and paper experience, but the approach lacks some of the other features I would like.   How do you document your projects? Do you know of any app that approaches my needs?   Aubrey Kagan

I had an interesting discussion with Robert Cravotta regarding four-bit processors. He came up with the Embedded Processing Directory which lists a good number of CPUs, but tiny 4 bitters aren't included. Does that mean they're dead?   Apparently not. In a post about the subject, Robert identifies several areas where these microcontrollers are still steadily cranking away. One example is the Gillette Fusion ProGlide razor , a "manual" device that incorporates a four-bitter. "Manual" is in quotes since it is not electric, other than the circuitry included for running the CPU and powering whatever it is the software controls.   A gift pack that includes the razor and a number of other manly-grooming accessories costs a mere $8.50 in stores. The razor itself has got to run just a buck or two in manufacturing costs. Even an 8 bit CPU that costs a couple of dimes would eat too much of the BOM. I wonder what the microcontroller costs in the millions of units Gillette buys? It must be pennies.   Breathtaking volumes of low-end products scream for the cost advantages of a truly tiny processor.   It seems, though, that 4 bits has fallen off the radar. The processors are never covered in the press. It's hard to even find datasheets. Here's one for the EM6580 from EM Microelectronic. I'm unable to find a programming guide, but the datasheet claims this is a four bit controller with 72 instructions, suggesting it's a long cry from a RISC device.   Small isn't new. Motorola had a single-bit CPU in the 70s that assembled the bit stream into (internal) four bit instructions. Way cool, but hardly new even then. Data General's Nova 1200 minicomputer was a 16 bit machine with a four bit ALU. Logic sequenced operations through the ALU a nibble at a time. The result: Novas were cheap, at least for computers in the pre-microprocessor age.   They were "embedded" in all sorts of applications. We put them into instrumentation. Though we yearned for the much nicer architecture of DEC's PDP-11 units, the price difference made that impossible. Cost has always been an important engineering consideration, which surely is the motivation behind today's continued use of nibble-wide CPUs.   Do you use really low-end processors? Which ones and why?