James Munns

Chief Whiteboarding Engineer

OneVariable Newsletter - 2022-01-12

2022-01-12

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Abstract and Results

Happy new year! I took the last week off of the newsletter, as I found myself stuck and a little frustrated with the progress on getting the network stack up and running.

I did get the RS-485 network stack re-integrated with Anachro, at least enough to compile, but I haven't sat down to work through the integration bugs and get the full communications stack stable and running.

After a couple of tedious weeks troubleshooting some challenging driver problems, I needed some "easy gimmes" to get myself back excited to work on the Powerbus Mini stack.

Since I don't have a deadline, it was more fun to give myself a distraction for a week or two to recharge!

So this week, enjoy a small highlight reel of the one-off and conceptual projects I worked on instead!

Here's a quick list to get started:

Background Information

First off, I built three more Powerbus Mini boards. While assembling, I did have a couple of issues, where two of the boards refused to interface with the Flash chip over QSPI, and one board where the USB port did not have a reliable connection.

While trying to fix the USB port with a hot air station, I managed to break the board in some other way, so this board is unfortunately out of operation, at least for now. Rather than rework the other boards, I noticed that "regular SPI" mode still worked on the other two boards, so I'm using that as a workaround for now.

A whole family picture of the current batch of Powerbus Minis

A table containing four powerbus-mini circuit boards, and their assorted accessories

My first "distraction" project was to assemble and integrate an Adafruit Mini Pan/Tilt Servo Kit. I used a Powerbus Expansion card to break out the 5V rail in order to power the servos, and two PWM lines from the nRF52 to control them.

I haven't done much with this project yet, but it was fun to get the motors up and moving, as a change from my typical "all LEDs" output. You can see a short video of the servos in "party mode" here:

Powerbus x Pan/Tilt Servo Kit Collab

A powerbus mini with attached servo pan/tilt kit

I think in the future, I'll mount two or more of my 6x8 LED character displays acting as "eyes", to make a little emotive robot friend. You can check out Lixie Lab's Pixie Chroma Test Jig for the kind of things that are possible! I might even add a third servo for the "face", so the robot can do the cute "dog head tilt" emote.

6x8 LED character displays

Lixie Labs Test Jig

Next up, I wanted to try out some of the White/Warm White/Amber LED strips that I ordered a while back, to use as ambient lighting around my house.

You can see the full one meter light bar (in an aluminum housing with diffuser) above in the "family picture", but I also built two special accessories for this project: A power dongle, and a user-interface board.

Light Bar Controller Components

A powerbus mini, a control board with a potentiometer, button, and hook-probe cables, and a hand-made USB-C socket to Barrel Plug adapter

The first (shown at the bottom) "USB-C to Barrel Plug" adapter cable, which includes a "USB-C Decoy", which negotiates 20V3A power from a USB-PD supply, like you would use with a laptop or tablet charger.

The second (shown top right) is a simple board that contains a 10K potentiometer dial, as well as a single button. I designed this with hook probes, so I could tweak around the connections, but it is annoyingly easy to detach, so I'll probably remake the input board on an Expansion card.

One deployed Light Bar!

An LED bar mounted behind a couch, shining a bar of warm white light upwards

I can cycle between the different LED colors with the button, and change the level of each color with the potentiometer. This lets me tune the color temperature of the LED bar. In the future, this will also be controllable over the network.

I also used some wire-wrap wire to firmly attach the LED bar to the Powerbus Mini, which is currently hanging out behind my couch.

Activity Tracker Block Diagram and thread

As a larger, more directly usable project, I started working on an "activity tracker", which will let me log certain activities, like eating well, or going on a walk, or taking time to meditate or read a book, to give me a visible "health bar" of how well I'm taking care of myself.

For input, I'm using a Solder Party Keyboard FeatherWing, which has a Blackberry Q10 keyboard, and a 320x240 LCD display.

Activity Tracker Parts Connected

A powerbus mini, a 'USB-C pill' as a debugger, and a Keyboard FeatherWing

Since the Keyboard FeatherWing has an Adafruit Feather slot on the back for the main microcontroller, I needed an adapter to connect the LCD SPI and Keyboard I2C lines to the Powerbus Expansion card.

I built a wiring harness using an expansion card on one side, and a FeatherWing Proto board on the other side.

Wire Wrapped Board Connections

A close-up of a Powerbus Mini expansion card, with a wire wrapped connector, and hot glue strain relief A close-up of a FeatherWing Proto card, with a wire wrapped connector, and hot glue strain relief

I used wire wrapping to make the connections, with a bit of hot-glue to act as strain relief on each side. This should be reliable enough for now, and might even serve as the final "production" cable, if it ends up being long enough. I plan to mount the Keyboard FeatherWing on a flexible cable with a "holster", sort of like the Video Game Kiosks you'd see in stores.

Hackaday Wire Wrapping Introduction

PC-side UI mock-up

A mocked up user interface displaying a 'fuzzy search' behavior

I spent some time with the embedded-graphics crate to build a user interface for the tracker. Since embedded-graphics come with an excellent simulator, I was able to prototype and build this quickly on my PC, and transfer the code 1:1 to the Powerbus hardware.

I took some videos of the menu drawing on the Powerbus Mini assembly, as well as a recording of the desktop simulator showing the "fuzzy search" and selection interface.

Drawing on-target

Fuzzy search

Finally, I was able to write and publish the toml-cfg crate, which I plan to use to simplify some of the ubiquitous const-generic parameters I use across the Anachro network stack.

If you find yourself looking for configuration values that aren't binary flags like Cargo supports, it might be a useful way to move those from code into a config file!

Suggestions for Future Research

Phew! That was a lot of fun and small projects. But it's probably about time to get the network stack verified, so I can make sure the RS-485 hardware works, and make the next hardware revision fixing a couple of the known papercuts with the current Powerbus-Mini hardware.

I'll probably aim to keep that as my primary focus, with the activity tracker as my fun back-up project.

Stay tuned for more updates, and thanks for following along!

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