This is a program that returns 3 as an example.

First, write the source code in C.

// three.c
#include <ruby.h>

static VALUE int_three(void){
   return INT2NUM(3);
}

void Init_three(void){
   rb_define_singleton_method(rb_cInteger, "three", int_three, 0);
}

Create a script to create a Makefile.

# extcof.rb
require 'mkmf'
create_makfile "three"

Make

$ make

Write a Ruby script to call the created program.

# main.rb
require "./three"
p Integer.three

Run

$ ruby main.rb
3

Notes on creating a DLL and compiling C​

Library​

Source file​

// gcd.c
int gcd(int a, int b){
   return !b ? a : gcd(b, a % b);
}

Header file​

// gcd.h
#ifndef TEST_H
#define TEST_H

int gcd(int a, int b);

#endif

Program​

#include <stdio.h>
#include "gcd.h"

int main(void){
   printf("%d\n", gcd(24, 36));
}

Compilation​

Creating the DLL​

gcc gcd.c -shared -o gcd.dll

Compile​

gcc main.c -lgcd -L.

I tried creating realistic terrain in Unity.

Created based on satellite imagery and elevation data from the Geospatial Information Authority of Japan.

Next, I'd like to create Kyushu.

Last time, I tried soldering the etched PCB.

However, the circuit was wrong, so I remade the board.

I made a printed circuit board for developing a homemade measuring instrument.

Acetone Transfer​

Print on plain paper with a laser printer, then place the printout on a copper board, wet it with water, and press the paper firmly. Next, apply a small amount of acetone and, from above a clear file, rub the toner onto the copper board with your fingernail to transfer it with acetone. The first time, I used too much acetone and failed. It's just right when it's soaked throughout. I used 100% acetone nail polish remover.

Wash and rub with water to remove the paper.

Etching​

Pour the etching solution into a suitable container and warm the solution to body temperature using a freezer bag filled with hot water for etching. Around 40 to 45℃ seems to be good, but I didn't use a thermometer as it would rust, so I just estimated. Visually confirm that the copper in the unmasked areas has dissolved, then stop etching.

Dissolving the Coated Parts​

Dissolve the parts masked with toner or permanent marker using acetone. This leaves only the copper in the masked areas, creating the circuit.

Making a Small Circuit​

I drilled holes and soldered to make a small circuit. It was easier to solder by applying it as if laying it on top of the copper.