An improved dsPIC-EL-GM

It was way back in 2012 when I first started thinking about a dsPIC-EL, but it was 2015 when I finally broke down and sent a PCB to production.  Since then the dsPIC-EL-GM has been the foundation for dozens, maybe hundreds of projects.

Recently I find I am dealing with many more 3 volt parts, and I often end up building a 3V3 supply on whatever shield I am making at the time.  The basic board has plenty of proto space which I never use, so why not sacrifice some of that for a 3 volt regulator?  The Arduino shield has a pin for 3 volts, so that wasn't a big deal.

3V3 supply

Turns out to have been a pretty simple change, and I was running out of boards and probably would need to order more anyway.  The one disappointment was that I paid extra for DHL shipping, and due to customs delays, Chinese holidays, etc. the board took almost as long as free shipping. Well, that and Maker Studio no longer makes custom boards so I had to search out other suppliers.

Things have changed over the past few years. The price of Chinese boards has come down a little, but the price for U.S. made boards has exploded. It used to cost less than three times as much for a U.S. board over a Chinese board. Now it is more than ten times. Plus, I can get Chinese boards just as quickly as U.S. boards, so even paying a premium for fast shipping, they are still a lot cheaper.

One minor annoyance in the old board was that the contrast pot for the LCD couldn't be adjusted when a shield was in place. I tried drilling a hole in the shield, and even laid out a new shield PCB (but never ordered it).  It occurred to me that I could fit a vertical pot under the LCD.

New contrast pot location

With that change, I could now adjust the LCD contrast without messing with the shield.  (Yes, I know, how often do you need to do that. Well, I play with various LCDs, kind of a fetish I have, so I probably twiddle that pot more than the average bear.)

While I was at it, I decided I would change the bypass caps out for SMT caps. Don't know why, I have hundreds of 0.1 and 0.01 monolithics in the parts drawer, but it seemed like the thing to do.  What I didn't do is change out the resistors, which I probably should have.

dsPIC-EL-GM full board

The other thing I really should have done is used SMT LEDs. The 5mm LEDs sometimes get in the way. On one instance I did tack SMT LEDs on to the through hole pads, and that worked quite well.

I'm pretty pleased with this board. Although there are a few things I would like to change, nothing is really pressing, so probably this will be the last change for a while.

As always, the PCB file, Gerbers, etc are all in gitlab. This version is in the Rev2 branch.

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.

More on the dsPIC-EL

OK, so a few months down the road we can give a progress report on the dsPIC-EL and the high school club.

Solderless Breadboard

First of all, the members of the high school Electronics and Wireless Communications Club are wicked smart.  These kids are just unbelievable.  Before building the dsPIC-EL boards we gave them a handful of parts, a solderless breadboard, a schematic, and asked them to make the LED blink.  Your standard first PIC project, but the guidance they got was very limited.  All of the students had little problem accomplishing the task (for that one we used the PIC24FV16KM202 because at the time we didn't have enough of an inventory of dsPICs for all the club members.)

We felt it was useful to start with a "from scratch" sort of build so the club members understood that they don't need to buy an Arduino or some prepared kit to do something interesting.  They are prefectly capable of doing whatever they want.

After they had the LED blinking we gave them a few more LEDs and resistors and told them to play.  Interesting results, and I think it is useful for them to go off with little guidance and explore on their own.

dsPIC-EL-GM

They then built the dsPIC-EL.  The provided dsPIC33EV32GM002 contained an acceptance test so they could see right away that they were successful. (Refer to the construction instructions link on the previous post.) A provided library for the LCD allowed the club members to experiment with the buttons and LEDs and display what they were doing.

Shield with DS1821 annotated

Next up was to add sensing. The ultimate goal is to do a high altitude balloon launch in the spring.  This balloon is to carry a payload containing sensors for those measurements of interest to the club members.  A shield was built for the dsPIC-EL containing a DS1821 digital thermostat.  Again, a library was provided to ease the handling of the Dallas One Wire protocol.

LDR voltage divider

For sensing, analog input will be a must, so next the students added a light dependent resistor to their shield and learned how to read voltage.

The final, sort of "directed" experiment was to add a serial EEPROM to the shield.  In the spring launch, this will be needed to store the measurements for analysis after the payload is recovered.

24FC128 SEEPROM

The club members then split into small teams of two or three members.  One team was responsible for the control processor, one for the storage processor, and the remainder for each sensor module.  The plan is for each sensor to take commands from the control processor, report the measurement, and then have the storage processor store the result.  K8VFO guided the teams in preparing functional specifications and then designs for each of the modules.  Students did Internet research to select sensors and are currently working on firmware for each module.

Initial testing and development is being done on the dsPIC-EL, but the launch payload will use a dsPIC-EL for the control processor, and purpose-built shields for the measurement modules.

K8VFO is also walking the club members through the process of converting their schematics to a PCB layout, sending the design out to manufacture, and testing the resulting board.

Of course, some of our stronger club members will be graduating about the time we do the launch.  We hope the remaining members will return in the fall when we plan to build on this year's progress and address telemetry from the balloon to an earth station.

As I said, these kids are wicked smart.

A working dsPIC-EL

After deciding a long time ago that I wouldn't do a dsPIC-EL, nor an Elmer 166, I decided to do a dsPIC-EL, but the Elmer 166 is only kind of.

When I broke down and did the club thermometer project (http://elmer166.blogspot.com/2015/08/club-project-thermometer.html) I realized how straightforward a PCB can be.  OK, I am clumsy at it and it takes a few cycles, but the result is very satisfying.

The PIC24FV16KM202 used in the thermometer, and it's sister the PIC24FV32KA302 were something of a revalation.  The peripheral complement is absolutely breathtaking, and the peripheral pin select allows for a lot more flexibility than the dsPIC30F family.

I ran into to project where I wanted a little more speed, and tripped across the dsPIC33EV256GM102.  Astonishing!  70 MIPS, gobs of memory, PPS like the 24FV, and the family of dsPIC33EVxxGMyzz lets you select memory size, pin count, and network from a family of otherwise identical parts.

I started working on a dsPIC-EL board based on this part, and realized that the pinout was virtually identical to the PIC24FV series.  I could choose between dsPIC33EVxxGMx02, PIC24FV16KM202, and PIC24FVxxKAy02 parts by the simple addition of a jumper.

dsPIC-EL

From the work on the dsPIC30F board I recognized that Arduino-style header connectors were a worthwhile addition.  With the thermometer project I had also recognized that I could get proto boards custom made for less money and higher quality than I could buy already made. It was a short step to realizing that if I bought the long pin headers used by Arduino shields in quantity, I could have shields for under three bucks.

dsPIC-EL with proto shield fitted

Somewhere around this time I got roped into working with the high school electronics club.  The students early on expressed a strong interest in building stuff they could program.  This, of course, pushed me into moving along much quicker on the dsPIC-EL, and I can pretty much call it soup now.

Of course, I want to share this development, so all the work is on GitLab, but I have no interest in kitting the thing.  The good news is that the boards can be had quite cheaply, and there are really no hard parts (although some parts are a lot cheaper in quantity).  If all the parts were purchased in quantity one, I suspect it could be had for around the cost of a PIC-EL.  Buying things like connectors in quantity cuts the cost to less than half.  The main disadvantage to some of the large quantity parts is lead time.

The dsPIC33EV256GM102 is kind of pricey, but the 32K version without the CAN (which is unlikely to be needed) can be had for less than the price of a PIC24FV, which itself makes 16F and 18F parts look expensive.

So, the main features:

• PIC with pins brought out to Arduino connectors for easy prototyping
• Extra connector to allow ordinary perfboard to be used as a shield
• LCD and buttons on the base board.  You always want these, and they have the annoying feature of needing to be on the "top" shield which really limits flexibility if they are on a shield.
• All used pins jumpered so they can be used for prototyping without interference from on-board parts
• A few LEDs thrown in for good measure
• Power from a cell phone charger with an XH connector for batteries or some other external supply
• PICkit connector for programming
• Jumper to allow PIC24FV to be used

Schematic

I don't plan to do another Elmer 160 type class, but I will be guiding the high school club's members through learning the dsPIC, and I will be putting my materials on GitLab, so they will be available to anyone who is interested.  Rather than PDF prose, most will be PowerPoint (well, actually LibreOffice).  Of course, high school kids pick up things a lot quicker than us old hams, so the material will be quite a bit different.

The key repositories are:

The PCB including Gerbers.  The README for this repository includes the schematic and a red/blue image of the board.  The BOM in this repository also contains information on sources.
https://gitlab.com/33E-simple/dsPIC-EL-GM

The ProtoShield gerbers
https://gitlab.com/33E-simple/ProtoShield

An LCD library
https://gitlab.com/33EV-GM1/LCD.X

An I2C library
https://gitlab.com/33EV-GM1/I2C.X

Presentations (under development)
https://gitlab.com/33EV-GM1/dsPIC-presentations

Construction instructions (under development)
https://gitlab.com/E-WCC/dsPIC-EL_Build_Instructions

If you want to get boards made, simply upload the zip file containing the Gerbers to
http://makerstudio.cc/index.php?main_page=product_info&cPath=8&products_id=14
The price is around $16 for 10 boards including shipping.  Shipping seems to vary a bit, I assume based on exchange rates.  It takes about three weeks for the boards to reach the U.S.  I have also used Accutrace in cases where I want boards a little sooner (8 days).  Their price of $40 for 10 is quite a bit higher than MakerStudio, but not crazy, and their customer service is tops.  Their boards are a little higher quality than the Chinese boards, but you need to look really close to tell the difference.