Author: scruss

The greatest common divisor (gcd) of two natural numbers is the largest number that evenly divides both. For instance gcd(8, 12) is 4. There are many clever and efficient ways to calculate the gcd of two numbers on a Linux machine. The method presented here is not among them.

#!/bin/bash
gcd(){ comm -12 --nocheck-order <(factor $1|sed 's/^[^ ]*/1/;s/ /\n/g') <(factor $2|sed 's/^[^ ]*/1/;s/ /\n/g')|tr '\n' \*|sed 's/.$/\n/'|bc;}
gcd $1 $2 

(Contrived) example:

gcd.sh 24691357802469135780246913578 61728394506172839450617283945
12345678901234567890123456789

Which breaks down as:

Multiply the factors common to both:

3 × 3 × 3 × 7 × 13 × 31 × 37 × 211 × 241 × 2161 × 3607 × 3803 × 2906161 = 12345678901234567890123456789

I’m sure someone else has used the output of factor and comm in this way before. The hard part was getting coprime numbers to output 1.

The greatest common divisor (gcd) of two natural numbers is the largest number that evenly divides both. For instance gcd(8, 12) is 4. There are many clever and efficient ways...

So I picked up this large boy from the MSU Surplus Store:

You get about 7 high-resolution pictures on a disk. And high resolution by 1998 standards means this:

1024×768 whole pixels: that’s huge! The camera is autofocus with image stabilization, so it was quite a nifty unit at the time.

Pre-dating EXIF, its image metadata is limited. There’s an external ‘411’ thumbnail file that looks a bit like this:

If you care to dig about in such an ancient file, I’ve got a matching image and its 411 file here: MVC-005X.zip. And manuals? Here: Sony_Mavica-FDC91-W0007229M.pdf

Most annoyingly, the camera really only likes real Sony batteries, or it shuts down with an “InfoLithium” battery error. As this battery format is now used in generate photo lighting systems and Sony don’t make it any more, this may be a camera that dies from DRM before anything else.

So I picked up this large boy from the MSU Surplus Store: Sony Digital Mavica MVC-FD91 (c. 1998 CE) — yes, that’s a 3½” floppy drive on there You get...

Simple things like fasteners don’t seem to be invented. It’s almost as if they’ve always been around. Like T-nuts — those hammer-in furniture nuts that also find use as 3D printable tripod mounts — someone invented those?

Sure enough, it seems that local company Sigma Tool & Machine have a lot to do with T-nut development. They’re now on Nantucket Blvd just north of me, and they used to be at 96 Crockford Blvd very close by.

from US Patent 3480061 ‘Fastener member’ by W. H. Leistner, granted 1969-11-25 Simple things like fasteners don’t seem to be invented. It’s almost as if they’ve always been around. Like...

This may not look much, but it’s a test build of Vik Olliver’s Quirkey USB chord keyboard. I didn’t quite build it to Vik’s specs, which are here:

• code: VikOlliver/Microwriter: A reboot of the 80’s Microwriter accessible chord keyboard done using an Arduino
• case: Quirkey Chord Keyboard Shell

The Microwriter was a late 1970s/early 1980s gadget that was essentially a portable word processor. Unusually, its keyboard was a single-hand 6 key layout — the thumb did double duty — that was operated by chording multiple keys at the same time. Later on in the Microwriter’s life it evolved into the Quinkey, a chording adaptive keyboard for computers of the time.

Technology has moved on a bit, and the ability to wire up a cheap USB-capable microcontroller and 3d print your own case is here. I used an Arduino Micro on a breadboard and six Omron momentary buttons.

I didn’t quite wire it the way that Vik intended:

The buttons are wired like this:

Pin      Button
=======  =======
 D8       Control
 D7       Thumb
 D6       Index
 D5       Middle
 D4       Ring
 D3       Pinkie

This requires changing line 22 of Vik’s code from:

const int keyPorts[] = {8, 7, 6, 5, 4, 9};

to

const int keyPorts[] = {8, 3, 4, 5, 6, 7};

While there are great tutorials on “microwriting” in the original manuals on Bill Buxton’s site, here are the basic alphabetic set derived from Vik’s code:

Thumb
|Index
||Middle
|||Ring
||||Pinkie
●○○○○ : Space
○●○○○ : e
●●○○○ : i
○○●○○ : o
●○●○○ : c
○●●○○ : a
●●●○○ : d
○○○●○ : s
●○○●○ : k
○●○●○ : t
●●○●○ : r
○○●●○ : n
●○●●○ : y
○●●●○ : .
●●●●○ : f
○○○○● : u
●○○○● : h
○●○○● : v
●●○○● : l
○○●○● : q
●○●○● : z
○●●○● : -
●●●○● : '
○○○●● : g
●○○●● : j
○●○●● : ,
●●○●● : w
○○●●● : b
●○●●● : x
○●●●● : m
●●●●● : p

The astute reader may note that these are binary values (low bit to high) of the character positions in Vik’s alphaTable variable. And yes, that’s supposed to be preformatted text.

Happy microwriting!

This may not look much, but it’s a test build of Vik Olliver’s Quirkey USB chord keyboard. I didn’t quite build it to Vik’s specs, which are here: code: VikOlliver/Microwriter:...

Buttons, Tactile switches, Momentaries, Clickies, SPST-NO; call ’em what you will, but my world seems to be full of them right now. Wiring them or breadboarding them may not be as simple as they look.

Whether they are the tiny 6 mm ones of the less-easily-lost 12 mm ones, both types typically have four pins or legs, two on the top and two on the bottom. If your appear to have the legs on the sides, flip ’em 90°: they won’t fit in breadboard sockets the wrong way.

The pins on the left and right side are common, so connecting top left to bottom left won’t ever change state if you press the button. So use either the pins both on the same side or those diagonally opposed if you want the switch to work.

You can use these buttons on a common breadboard rail. You must remember to have only one button pin connecting to the rail; lift the other pin so it won’t connect. You can then use just one wire connected diagonally across the the common rail pin and you’ve got a working button. This is especially useful when using a microcontroller with built-in pull up resistors (that’s most of them these days).

If you connect both pins to a common rail, you’ve just made a SPST-AO (single pole, single throw – always open) switch. Those aren’t much use at all.

The right and wrong ways to connect buttons Buttons, Tactile switches, Momentaries, Clickies, SPST-NO; call ’em what you will, but my world seems to be full of them right now....