PROJECTS: SPEED VEST
Time: 1-2 Weekends Complexity: Moderate
1. ASSEMBLE THE PROTOSHIELD
The ProtoShield lets you build circuits directly on top of the Arduino board. I assembled it following
Atomicsalad’s excellent ProtoShield tutorial, linked at makezine.com/19/speedvest.
If you’re really in a hurry, you can leave out all the female headers. But if you might use your ProtoShield for
other projects later, it’s better to assemble the whole thing (and you’ll still have to do a lot of desoldering.)
2. BUILD THE CONTROL CIRCUIT
For each display digit, an Arduino output pin connects through one resistor to one triac. The other 2 pins
of the triac connect to ground and the digit’s ribbon cable pin. It’s a simple circuit; the tricky part is fitting
12 of them onto the ProtoShield. (There are too many connections to use the ProtoShield’s mini solderless
breadboard.) Here’s how I did it. Refer to the schematic at makezine.com/19/speedvest for all connections.
2a. Plug the 2× 7 male header across the middle of the board, perpendicular to the rails and with one end
adjacent to the ground (GND) rail.
2b. Plug in the 100Ω resistors just below the 5V rail in 2 rows of 6,
grouped on either side of the male header. Underneath, connect
one end of each to one of the D0–D13 contacts, on the female
headers if present, or else on the board itself. Leave D3 empty for
the speedo interrupt. To save room, orient the resistors vertically.
2c. Arrange triacs at the intersection of each resistor and
header pin. For each triac, the gate lead (pin 2, the middle pin)
will connect through a resistor to one of the Arduino’s digital
outputs D0–D13. This pin controls the flow between the other
2, like the base of a transistor. Pin 1 of the triac, on the left as
you read the printing on its face, connects to ground, and pin 3
connects to the ribbon cable via the 2× 7 male header.
104 Make: Volume 19