Divide and conquer

Welcome to the blog post I wish I had read two days ago.

From now on I will make it a rule to get one peripheral working at a time. Why? Because it turns out if you don’t; they might interfere with each other in a bad way.

This particular one saved us a PCB spin. If I did not get the devkit, this is one of the things I could not foresee. That’s why my new rule is to test one peripheral at the time, then together!

Maybe it is getting a screen working, reading from an SD card or simply getting I2C working. Get them working one at a time, then together. Oh, and did I say I2C is simple? Let me take you on my ~20 hour journey getting it to work in my setup!

Devkit has arrived!

Just a short update from me today: I received the devkit from WaveShare (only two days, wow) and it looks good! I like the layout and there’s excellent documentation. Of course the mechanical aspects are all on the cheaper side, but what do you expect for this price? Over all I’m super happy so far and would recommend anyone looking for a devkit, to search their site for something appropriate (not affiliated).

 

Design for Debug

I’m not formally educated as an electronics engineer, though I am a software engineer. One of the things that happens with engineering is that you make mistakes. Because of this, I always design my first revision of a PCB for debugging.

This means that is has to be easy to test voltages, configure boot states and isolate  the various functional blocs of the design. Things of particular interests could be; power supply, charge circuits, external peripherals (DAC, ADC, Shift registers, LCD, encoder etc) and whatever that’s new for you at the time.

Let’s dive into the few and simple techniques I use when I intentionally design for debug!

System Workbench for STM32

I love it when mCU manufacturers makes it easy to get started for free. Even more when they use technologies I know from before. No esoteric compiler, no weird debugging system I’d have to learn and research.

When I started this blog post I thought I’d have to document many steps in order to get to tool-chain and the IDE up and running, but I was wrong.

First pass parsing MIDI

Sample MIDI

So. What is this MIDI stuff anyways? I touched on it while I said specifications can be fun and it’s about time I dive further into this rather old technology.

A communications protocol for musical instruments

At the core the title says it all. It’s a serial protocol that can be driven by a UART at 31250 baud.

First pass layout

First pass PCB layout

I’ve just done a quick layout, as I usually do. Why so soon? To uncover potential problems down the line! Did I find one already? Yes.

Enclosure jungle

I’m going nuts with all the various enclosure sources, but none seem to really fit my bill!

There is a need to settle down on an enclosure before this project can go much further as it will dictate the various dimensions on all the rest of the parts.

I’ll give you a short list so you can see what I’m up against!

Development kit

I’s been my experience that when setting out to design a custom PCB on a new chip it pays to have some known board to debug off of. This can be useful even if there’s no relevant peripherals on there. Either add them, or simulate them, or maybe even double check that that pin actually is tristated when it’s supposed to!

MCU jungle

One of the many important choices when starting a hardware project is to choose the part that is going to be what everything else revolves around. Namely the Microcontroller.

I knew my minimum requirements were something like this:

• 1 SPI
• 2 I²S with master clock out
• 1 I²C
• 1 U(S)ART
• LCD 8080/6800 parallel peripheral
• MMC/SDIO
• USB FS (pref HS) Device

These all need to be accessible at the same time, so I don’t want to keep reconfiguring pins and all that jazz. I want a chip powerful enough to comfortably do what I want it to do. Comfortably for me, that is.

Specifications can be fun

Specifications I know. I usually get them from other people. At least I did. Just like those sentences, I can with this project – do whatever seems appropriate. Like ugly long sentences, that are hard to read because I make you look for that period until you mind is figuratively (and even make unnecessary asides just to let you know that “literally” would be entirely wrong in this context; and you already knew that) exhausted.

Specifications are easy!