— Tanner Stokes (@TannerStokes) October 29, 2021
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Category: Projects
I saw flip dots (also called flip discs) last year for the first time and instantly knew I needed some in my life. If you’re not familiar with them, check out how they work!
The particular model I have is the ALFAZETA XY5, which may be the easiest way to get up and running, but certainly not the least expensive.
After getting the board, all you need is:
- 24V power supply
- Something that talks over RS485 (in my case I used an ESP8266 connected to a MAX3485 board)
- Their documentation that defines the controller data protocol
I plan to write in more detail how it all works, but for this demo the stack is:
- SwiftUI app that runs SwiftGFXWrapper (which is mainly Adafruit’s GFX Library under the hood)
- The app sends the entire pixel buffer over UDP to the ESP8266
- The ESP8266 sends data to the XY5 over RS485 using their controller’s protocol
For even easier prototyping, I’ve added Swift Playground support to my SwiftGFXWrapper project!
It felt good to complete this project that’s been on my list for quite some time. The main goal was to scrape the values from my modem’s status page and pipe them into InfluxDB, which feeds Grafana. Not only could I look at data trends, but I could receive alerts if certain values exceeded an acceptable threshold.
Overall this is a straightforward process:
- Pull in the HTML from the status page (which happens to not need any authentication, making it even easier)
- Parse the tables we care about (Downstream and Upstream) using XPaths
- Munge the data into something suitable for InfluxDB
- Insert the data into InfluxDB
- Query the InfluxDB data from Grafana
I knew I wanted to use Python for the project, so I first looked into Scrapy. After wrapping my mind around it (somewhat) I gave it a go and actually had a working solution… but it felt way over engineered and at times inflexible for what I wanted. I threw 90% of that solution away and went with a simpler script.
What I landed on was something that’s custom and lightweight, but extendable in case someone has a different status page or wants to use an alternative to InfluxDB.
Another fun project from a few weekends ago: Wrapping the Adafruit GFX in Objective C and bridging to Swift for some neat 8-bit effects!
The most interesting component of this project so far has been building a Swift closure that is executed in C as a const void *. This was new territory for me and a lot of fun to figure out!
Currently a work in progress, I’ve nerd sniped myself to get TCP/IP working over SLIP with a pair of Arduinos equipped with nRF24L01+ radios.
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Pi 1541 – it works!
After some initial struggles, we’re good to go!
At work we’re primarily using Zoom for meetings while we’re in remote mode. Due to the recent problems found in their desktop software, I run it only on my iPad to provide a little more security (thanks to iPadOS’ sandboxed environment), plus the front facing camera on my iPad Pro is superior to my iMac and MacBook Pro’s.
The first issue I found with this setup was that I wanted to get the iPad into a position more perpendicular like a web cam, rather than the angled up shot below my face. I don’t think anyone wants to look up my nose unless I’m on a telehealth call, so I ordered this flexible stand for about $25 from Amazon and got it mounted:
So far so good, until my first meeting. I wanted to follow conference call etiquette by muting myself when I wasn’t speaking, but it was a pain to reach and manually tap the mute button every time. Plus, although the flexible arm is super strong, it’s still going to wobble wildly if you touch the iPad and your video is going to show that.
Was there a way I could toggle muting myself without touching the iPad? After a quick Google search, the answer was YES!
The attached keyboard (Smart Keyboard Folio, Magic Keyboard) didn’t make any sense in this case, but a Bluetooth keyboard would be perfect!
Logical answer
The logical answer is to connect up a Bluetooth keyboard and hit Command + Shift + A when you want to toggle muting your mic, and you’re done. That’s it.
I’m not totally logical
Of course, the route I chose was different. I have enough keyboards on my desk, I really just want one button to do one thing.
Recently, I rigged a button to turn pages in the Books app over Bluetooth. We should be able to do the same thing here, right?
Figuring out the codes
The objective is clear: When we press a button, we send “command+shift+a” to the iPad.
Using Adafruit’s HID codes, we find:
- Left shift == 0x02
- a == 0x04
But what’s the “Command” button? Is that the “meta” or “GUI” key? If so, is it a modifier or just a regular key?
Lots o’ troubleshooting
I spent a lot of time troubleshooting over and over:
Compile a new sequence of commands, upload new firmware to the microcontroller, re-pair with the iPad, open Zoom and try to mute: No go.
From what I could tell, “shift + a” were working, but “shift + command + a” wasn’t. It wasn’t until I almost gave up that I had a breakthrough:
Let’s try remapping another key to “command” and see if we can press that key. How about Caps Lock?
It worked.
In my code I wrote:
// gold
ble.println("AT+BleKeyboardCode=02-00-39-00-00-00-00"); // shift + caps lock
ble.println("AT+BleKeyboardCode=02-00-04-00-00-00-00"); // shift + a
ble.println("AT+BleKeyboardCode=00-00");This is as if the user pressed “shift + caps lock”, and then “shift + a” at the same time, then released. Now the Zoom app was getting the proper command from a Bluetooth “keyboard”.
Hardware
This setup is virtually identical to what I have here, it’s just a different button.
The USB cable coming in is only for power, and if I had the Adafruit Feather version on hand I would’ve used that with a battery so the box would be totally wireless.
The button is no more complicated than this tutorial.
GitHub: https://github.com/twstokes/labs/tree/master/zoommuter
Improvements
A better version of this would be:
- A button to also toggle video
- Using the Adafruit Feather BLE version with a battery so the box would be entirely wireless
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Pi1541
After the fun and nostalgic experience of pulling our C64s out of storage, I wondered how someone could add new software in this day and age. It didn’t take me long to find Pi1541, which is:
a real-time, cycle exact, Commodore 1541 disk drive emulator that can run on a Raspberry Pi 3B, 3B+ or 3A+
https://cbm-pi1541.firebaseapp.com/
All I needed to do was provide an RPi 3, load some stuff to an SD card, make a cable, and I would magically have an emulated 1541!
Making a cable
I bought a high quality DIN 6 pin cable, some Dupont headers, and a crimping tool from Amazon to get it built. This guide (also linked from the Pi1541 page) set me on the right track.
The process to construct the cable was straightforward after teaching myself how in the world one crimps these tiny Dupont connectors. The trick is to line up and fasten the wire with some needle-nose pliers first, then carefully insert the connector in your crimp tool so you don’t destroy the “box end” where the male connector is received.
Connecting things up
I followed the “Option A” on the Pi1541 site for wiring since I wouldn’t be including any other peripherals. An important piece of this schematic is the bi-directional logic level converter. The RPi speaks 3.3V logic while the C64 speaks 5V.
I loaded up the SD card, connected everything, fired up the C64, and plugged in the RPi. Everything worked perfectly, right? Nope.
Trouble
At first the RPi didn’t boot at all – I had just a solid red light, so it was time to troubleshoot:
- Did I fry something on the Pi?
- Was the SD card bad?
- Did I load the software incorrectly to the card?
Good news: The Pi wasn’t dead. I confirmed this by booting from a spare SD card that had Raspbian loaded to it. Whew.
I then found the Pi would boot with the Pi1541 firmware, but only if the cables on the header pins were disconnected.
The culprit: The cheapo “bi-directional logic converter” I had lying around didn’t work at all like I assumed it did. Instead of supplying 3.3V and 5V to it (like it properly should), it only wants 5V. Turns out I was sending 3.3V to an output. Ouch.
Now we had a booting Pi with everything connected up, but still no disk drive:
Now we wait
After much troubleshooting I’ve come to the conclusion that I’ll just need to use a proper logic level shifter before proceeding. I’ve ordered some of these and will have to wait patiently as their expected arrival is the end of the month…