Blog

For it-seemed-like-a-good-idea-at-the-time reasons, I’ve ended up with a couple of tubes of the big dome LEDs. A tube is a lot; something over 20 pieces. Oh well, I’ll find uses for them eventually.

It seems these are LEDTronics 806 Series ‘Super Intensity 20mm Big Dome 6-Chip LEDs’. The datasheet shows they are configured as a DIP-12, with LED cathodes and anodes alternating around the pins:

The six LEDs are enough to use all of the available PWM pins on a regular Arduino. The green LEDs I have look like they’re supposed to take a current-limiting resistor of ≥ 75 Ω or so at 5 V. The 100 Ω resistors I used did pretty much max out the weedy regulator on the cheap Arduino Nano I was using, so you may want to use bigger resistors if you want to avoid having your USB disappear.

No Fritzing model of the part yet, but here’s a sketch that works, but quite fails to use any interesting PWM functions at all:

// do a whirly thing with the 6 LEDs inside a LEDTronics L806T_UG-LIME 20 mm Big Dome unit
// scruss - 2020-04
// https://www.ledtronics.com/Products/ProductsDetails.aspx?WP=281
// each thru 100R resistor - which might be rather small

#define MAXPINS 5
int pwmpins[] = { 3, 5, 6, 9, 10, 11 };
int i = 0;

void setup() {
  // pwm pins as output, all initially off
  for (i = 0; i <= MAXPINS; i++) {
    pinMode(pwmpins[i], OUTPUT);
    analogWrite(pwmpins[i], 0);
  }
}

void loop() {
  if (i > MAXPINS) {
    i = 0;
  }
  analogWrite(pwmpins[i], 255);
  analogWrite((i > 0) ? pwmpins[i - 1] : pwmpins[MAXPINS], 0);
  delay(30);
  i++;
}

or if you must: Ender-3 plays LG on YouTube.

I’ll admit that this version is strongly influenced by Washing Machine Sheet music for Percussion, which seems to have a couple of off notes.

Midi, MuseScore, gcode and PDF file:

But this is mostly about the discovery of I wrote a program that converts MIDI files to G-Code, enabling my printer to play music with its LCD buzzer on reddit, with the converter at: MIDI to M300

So here’s the gcode to play this:

M300 P632 S554
M300 P35 S0
M300 P222 S740
M300 P222 S698
M300 P222 S622
M300 P632 S554
M300 P35 S0
M300 P632 S466
M300 P35 S0
M300 P222 S494
M300 P222 S466
M300 P222 S494
M300 P222 S415
M300 P222 S466
M300 P222 S494
M300 P632 S466
M300 P35 S0
M300 P632 S554
M300 P35 S0
M300 P632 S554
M300 P35 S0
M300 P222 S740
M300 P222 S698
M300 P222 S622
M300 P632 S554
M300 P35 S0
M300 P632 S740
M300 P35 S0
M300 P222 S740
M300 P222 S831
M300 P222 S740
M300 P222 S698
M300 P222 S622
M300 P222 S698
M300 P2532 S740

One of the quirks of the SBC6120-RBC boards I just built is that its serial port talks a protocol that’s very rarely seen these days: 7 bits, mark parity, 1 stop bit. minicom supports it, but seemingly can’t set it from the command line.

Kermit, of course, can. Kermit (not the frog, but named after him) is the connect-to-anything, with-anything comms package. It’s been in constant development since 1981, and there’s hardly a computer system that exists that it won’t run on. The Unix/Linux variant, C-Kermit, has an incredibly intricate hand-crafted makefile that predates autoconf or cmake or any of those newfangled toys. Unfortunately, though, this means it may need a lot of reading and a little hand to compile.

There may be some additional dependencies, but to build a simple version of C-Kermit 9.0.304 Dev.23 on Ubuntu 19.10 and Raspbian Buster you need this patch, and do something like:

mkdir ckermit
cd ckermit
wget http://www.kermitproject.org/ftp/kermit/test/tar/cku304-dev23.tar.gz
tar xvzf cku304-dev23.tar.gz
wget https://src.fedoraproject.org/rpms/ckermit/raw/master/f/ckermit-9.0.302-fix_build_with_glibc_2_28_and_earlier.patch
patch < ckermit-9.0.302-fix_build_with_glibc_2_28_and_earlier.patch
make linux

and it should build correctly. There are many, many options: make linux+ssl gives some extra network security features; make install puts it in the system path.

The command line I use to connect to the SBC6120-RBC is:

kermit -l /dev/ttyUSB0 -p m -b 38400 -m none -c

That drops you straight into a connection. To get you back to Kermit’s command mode, type Ctrl + \ + C.