Making The Pinhole
Cut out a piece of aluminium from the drinks can, about 15mm square. Place the aluminium onto some thick cardboard. Using the fine sewing needle or sharp pin, gently press into the centre of the aluminium. Twist the pin between your fingers while doing this so that it slowly "drills" a hole through the metal. Don't push down hard with the pin so that it goes straight through, the idea is to produce a very small hole with clean edges.
The ideal diameter of the pinhole is about 0.2mm, smaller is OK, larger and the images produced will be less sharp.
Colour the back of the pinhole black, again this should help reduce internal light reflections in the camera
Place the aluminium onto the box so that the pinhole is exactly in the centre of the square hole in the top of the box.
Tape the aluminium onto the box, securing all four sides