CIRCUITS

E

F

GH

Fig. E: Red paint undercoat. Fig. F: Black paint partially rubbed away along the edges, exposing the red undercoat for an antique effect.

Fig. G: Finished amp meter clock with the lid open to show the circuitry. Fig. H: Clock displaying the analog to a blinking 12:00.

To help line up the scales on the plates, I printed extra marks where the screw holes were. And so that the original scales would not show through the paper, I put the new scales on the backs of the plates, which were blank (and symmetrical).

Boxing It Up

This is the type of project that needs a good box, to display the meters and conceal the wires and such. My wife suggested that a nice wooden box would look good on the mantle, and we chose one at a local craft store.

Mounting the meters meant drilling a wide central hole for the back of the meter itself, surrounded evenly by 4 small holes for the mounting screws.

I made a paper template as a guide (Figure B, previous page) and drilled accordingly, but it was hard to get the mounting holes accurate enough, so I used a larger bit and a keyhole saw to clear out enough space for them to fit (Figure C). The meters all fit tightly in the central holes, so I didn’t bother putting nuts and washers on the mounting screws (Figure D).

For the power source, I considered putting batteries in the box, but the Arduino pulls 20mA–30mA, so even with D cells, they would need to be changed about every 5 weeks. Instead I decided to use a wall

168 Make: Volume 13

wart and ran the cord through a hole in the back of the box. The buttons for setting the clock and changing modes I left on the breadboard inside.

Finally, I wanted the box to be an aged black, to match our furniture. I accomplished this effect by first putting down a coat of red paint and allowing it to dry (Figure E). I then followed it with black and lightly wiped the wet paint off the edges, exposing small amounts of red underneath (Figure F).

The end result is a unique clock and a great conversation starter that can be displayed prominently in my home, and now in yours, too!

Gene Scogin is a computer programmer who enjoys a variety of hands-on projects.