// Diameter of the coin (mm)
diameter = 39;

// Height of the coin (mm)
height = 3.5;

// Engraving depth (mm)
depth = 0.4;

// Number of sides on your coin
sides = 360; // [3:360]

// How many spokes do you want?
spokes = 6; // [0:12]

// Text to display
text = "100";

// The font must be installed locally on your system
font = "Droid Sans:style=Bold";

fontScale = (
    sides == 3 ? 0.50
    : sides == 4 ? 0.80
    : sides == 5 ? 0.80
    : sides == 6 ? 0.90
    : 1.00
);

// Enough width to fit four digits
fontSize = diameter * 0.21 * fontScale;

// Rotate odd-numbers of sides to maximize width
rotation = (sides%2)?90:0;

module chip() {
    intersection() {
        cylinder(h=height, d=diameter, center=true, $fn=sides);
        union() {
            difference() {
                cube([diameter, diameter, height], center=true);
                difference() {
                    cylinder(h=height, d=diameter*0.8, center=true, $fn=sides);
                    cylinder(h=height, d=diameter*0.7, center=true, $fn=sides);
                }
            }

            spokeHeight = height - (2*depth);
            if (spokes == 0) {
                cube([diameter, diameter, spokeHeight], center=true);
            } else {
                spokeWidth = (diameter/spokes) * 0.8;
                rotate((sides+spokes)%2?90:0) {
                    for (i = [0 : 360/spokes : 360]) {
                        rotate(i) translate([diameter/2, 0, 0]) cube([diameter, spokeWidth, spokeHeight], center=true);
                    }
                }
            }
        }
    }
}

difference() {
    rotate(rotation) chip();
    translate([0, 0, height/2-depth])
        linear_extrude(height=depth+0.1, convexity = 10, twist = 0)
            text(text=text, font=font, size=fontSize, halign="center", valign="center");
}