Dual-core development board

So a while ago, I discovered the dsPIC33CH family of dual core digital signal controllers (dsPIC33CH128MP505).  I did considerable tinkering with the proto board I was using, and it was becoming clear that this is a nice part. I took it being a 3V3 part as kind of a downside, but there are more and more 3V3 peripherals, which is one reason I kept hacking up that proto board to try yet another thing.

So my dsPIC-EL-GM solved that problem for the dsPIC33EVxxxGMy02 parts (and some PIC24 parts, too).  I've probably done hundreds of experiments with that board because the shield makes it so easy to start a new project. In spite of custom shields being a fraction of the price of commercial proto shields, I still tend to tack on project after project, and have found it necessary to label the shields so I don't get frustrated with the wrong connections.

Custom Proto Shield

So the idea of a experimenter's board for the dsPIC33CHxxxMPyzz was born.  Problem is, the 33CH isn't available in DIP. I'm not frightened by the prospect of soldering a TQFP, but laying out the PCB was another thing entirely.  My original thought was to design for the MP505 (48 pin) part. But I didn't have a TQFP48 footprint, and I wasn't real confident I could make one.  With the 64 pin part, I could populate all the Arduino headers without sharing pins with onboard peripherals.

But it isn't all sweetness and light. The dsPIC33CH512MP506-I/PT is in a 10 mm package, which means there are a whole lot of pins real close together. By itself that wouldn't be a real big deal, but you need to DO something with those pins. And that means you are going to need vias, and vias take space.

Vias

As I got the board laid out, I got lots of errors that the foils were too close, but in many cases, there didn't seem to be a lot I could do about it. Eventually, I got the first attempt at the board laid out.

PCB image from layout program

It had been a while since I had a PCB made, and in the interim, my favorite manufacturer quit making custom boards. And then another couple of surprises.  Many fabricators won't make boards with traces a tight as I had, and many of those that would charged a premium. Another surprise; it used to be that I could get a board made stateside for about twice what a Chinese board cost. I could have it in about a week, as opposed to three weeks for Chinese. Since then, Chinese prices dropped a little, Chinese fast shipping got more realistic, and U.S. prices exploded.  Stateside boards now cost more than ten times what a Chinese board cost.

I did find that JLCPCB would do my board without a premium, and I could get shipping for a sane price. I could get a board shipped from China in one day longer than it used to take for U.S. boards, and half the price that the U.S. boards used to cost. To add insult (to the U.S. fabricators) to injury, they have a nice web site that lets you watch the progress of your boards through the manufacturing process, and they have an apparently very thorough board checking before it goes to manufacture. It took me several cycles to get it right, and more than once they emailed me with questions; once I did something odd but meant to, another I had an error and was able to correct it before the board went to manufacturing.

Completed Dev Board (no shield installed)

Since much of the challenge was getting the traces routed, I actually laid out the board without a schematic. Yes, there were a couple places I shot myself in the foot, but all in all, it wasn't too bad.  I figured I should have a schematic too, and got to work on that. Turns out the schematic for something with all those legs is almost as fraught as the PCB.

Schematic

I don't know if I'll think of other things that need to be done to this board.  A version of my Serial Graphics Terminal that avoids the use of I/O expanders has been on my radar for some time, but that requires the use of a TQFP100 part. This board may well give me the confidence to go ahead and attack that.

For now I have some playing with 3 volt gesture sensors I want to do.

As always, the gore is in gitlab.