Monday, July 24, 2017

A GPS adjusted clock



We recently got a new cable box.  The new box has a clock that is a little smaller than the old one, and my wife has a hard time seeing it. We had an LCD clock with huge letters but there just isn't enough light in the place we want it.

So, NE06 GPS modules are getting pretty cheap. Why not get some huge seven segment LEDs and build up a clock based on a GPS?  Turns out large LED displays are fairly hard to come by, and pretty expensive. Plus, all that wiring to all those pins is a pain.

Then it hit me: I have some TFT displays, not huge, but plenty adequate for inch or inch and a half high digits.  If I used the TFT, I wouldn't even have to build the board; I could use my serial graphics terminal board.

First step was to see if I could make huge letters without too much hassle (the largest font I have is only about 3/8" high).  The first whack isn't too bad. It will work, although I might yet do some prettying up of the font.



So, on to the GPS.

I started with my serial terminal code, which may have added more complexity than I needed, but it works.  This code fills a circular buffer with serial interrupts from the GPS and the mainline has to process the contents of the buffer. This makes missing characters less likely but it does mean the mainline is futzing with trying to understand whether there are characters in the buffer and identify the start and end of the GPS data.

Parsing the GPS data is tedious, but not especially difficult.  With the PIC32MX150F128B there is plenty of memory, so I can be pretty aggressive with my code.  Most of the code is the TFT library so the stuff I'm working on is pretty small anyway.

At this point I can get the time and coordinates (which I don't need).  I am displaying all sorts of values which eventually won't be used.



Next up is to get the date, and go through the tedious business of determining whether it is daylight savings or standard time. The correction is trivial but knowing when to apply it is a pain.

Following that I'll get after the PIC's real time clock calendar.  Supposedly the PIC can maintain the time to within a third of a second per month.  I'm not convinced can actually accomplish that, but adjusting it from time to time through the GPS should keep the time always correct.

Since even in the basement with overcast skies I can still see 8 to 11 satellites that might be overkill.  If I have too much trouble with the RTCC I might just skip that, but the next priority is the daylight savings time thing.

The code is currently partial, and pretty rough, but as always I keep everything in git and the current code is in gitlab:
    https://gitlab.com/PIC32MX/gpsTime.X

The board hardware is at
  https://gitlab.com/PIC32MX/tft-board-pcb

And the TFT library code at
   https://gitlab.com/PIC32MX/TFT.X

They will be updated as time goes on.

170807:
OK, so some code cleanup, and slightly larger digits, but still significant work to do:



The digits are actually a tan color, but it doesn't show in the picture.

Sunday, July 16, 2017

The dsPIC-EL-GM

It has been a long time since I wrote about the dsPIC-EL-GM. This thing has turned out to be a very successful tool for me.

Over the past couple of years, this has been the platform for dozens of projects.  In some cases the entire project was done on the board plus a shield. In others, it became the prototype for a purpose built board.

The choice of the dsPIC33EV was a good one.  Besides being 5 volts, meaning inexpensive displays work with it, it is fast, available in a variety of memory sizes (32-cheap, up to 256-huge), has a huge range of peripherals, and PPS.

The decision to put connectors for shields on the board turns out to be critical. Most projects need an LCD.  Hand wiring all those pins from the PIC to the display, plus power and programming (which I seemed to always get wrong) tended to present a barrier to starting new projects. With the shields I can just grab a shield and get started, and all the tedious stuff is behind me.

Plus, by having a standard part, standard display/LED/button pinouts, I have built up a number of libraries that make getting a project started easier and faster.

There are a couple of features that turn out not to have been so useful.  The jumper allowing me to use PIC24EV parts hasn't gotten used very much. I was attracted by the low price of some of those parts, but the 33EV32 isn't all that much more expensive, and it has more memory and way more speed.

Also, I had added a connector offset slightly from the shield connectors to allow me to plug in standard perfboards. But the extremely low cost of custom prototyping boards made that less useful. The demise of Radio Shack also shoved that feature into obscurity.  It was a significant advantage to be able to run down to the corner to get a perfboard. Now that it has to be mail order, I just keep an adequate supply of prototyping shields on hand.

I have been tempted to build another PIC-EL for one of the PIC32s. The PIC32MZ series offers blinding speed, crazy big memory, and even floating point. By having a flexible platform, the need for a DIP package is mitigated, and the price of the MZ, while not cheap, isn't really crazy. I had a lot of fun doing a graphics card with the PIC32MX250F128B, so I feel like the PIC32 isn't that alien of an animal.  But that is a project for another day.

I am not trying to sell dsPIC-ELs. However, needed information for building your own is available on gitlab:
  • Gerbers for the dsPIC-EL-GM are available here.
  • And for the proto shields here.
We did kit a few for the high school electronics club, which necessitated creating detailed construction instructions:
  • Build instructions here.
Should you build your own, let me know how you did in the comments below.


Saturday, January 14, 2017

Really ancient history

A long, long time ago, roughly around the time of the invention of the wheel, I did a series of lessons on 8-bit PICs. These lessons were very well received, downloaded thousands of times, and although aimed at hobbyists, many professionals also used them as an introduction to microcontrollers.

Craig Johnson made an experimenter's board to help with these lessons, which was originally kitted by the American QRP Club and later by Kanga U.S. Over the years this board underwent a couple of revisions, and is still available from Craig directly.

I have continued to get questions about these lessons, even though it is over a decade, and the target micro, the PIC16F84A, pretty long in the tooth.   Most of the more recent questions have to do with the development environment, which has changed pretty dramatically since MPLAB 6.

I finally broke down and decided to update a couple of the lessons, those that go into great detail about manipulating MPLAB.
Of course, I based them on MPLAB-X, rather than MPLAB 8.  MPLAB-X was pretty rough during the beta testing, but has evolved into quite a nice IDE. Reviewing these old MPLAB documents reminded me of just how much the environment has improved. I also updated the screenshots and some of the prose for Windows 10.  I don't use Windows much myself, but these days most people do, so it seemed to make sense.

The lessons are both available on gitlab in pdf; Lesson 3 which does some initial exploration of MPLAB-X which is available here, and Lesson 4 which explores the MPLAB-X simulator in some detail here.

 The only other lesson that is tempting is Lesson 11.  It goes into a lot of detail about manipulating a program called FPP, which is no longer available. The replacement, tho, hardly seems worth it.  On MPLAB-X with the PIC-EL III it reduces to "click this button".

So perhaps that will reduce the emails in the future.  In any event, it should make things easier for those who are finally getting around to doing Elmer 160.