sleeve pulleys, and rubber O-rings to turn them.
After piecing together some brackets, hex stand-offs, and various nuts and bolts on the floor of the
hardware store (they’re very patient with me) I had
the start of a conveyor belt. At home I mounted it on
a wooden tray meant for organizing cuff links and
pocket change (Figure 5). Sorry, Mom and Dad.
Using a perforated aluminum strip to form a
bracket (Figure 6), I mounted the RFID reader inside
the conveyor belt (Figures 7 and 8). Tiles dropped
on the middle of the belt would be read and then
conveyed off the end into a receptacle. I mounted a
DC motor to turn the conveyor belt pulley. The RFID
board has two 5V DC outputs, drawn from USB
power. There are Phidget library calls to turn them
on and off, so I figured I’d use one to light an orange
LED and one to turn the conveyor belt as each tile
was read. Problem was, my DC motor required 12V
at greater amperage than the board could supply.
I needed a switchable, external power supply. Time
to build a 5V relay circuit.
A relay is an electromagnetic switch that can use
low voltage to open or close a higher-voltage circuit.
I soldered a small 5V relay to a piece of perf board,
and added a protection diode across the relay coils
to prevent damage to the RFID board from the
collapsing magnetic field when the relay closes.
I added a resistor-and-LED circuit to the board as
well, which would act as a status light (Figure 9,
Once we got the board sending voltage to the
relay, and the relay switching power to my motor,
I realized that it was turning too fast. I couldn’t fit
any gear reduction into the space. My solution was
to loosen the tension of the motor on the pulley
belt and let the slippage turn the conveyor belt at a
slower speed. In the future I’d like to install a gear
head motor to slow it down further and add torque.
I cut a cardboard poster tube down to 2 lengths
that would fit between my pulley wheels (Figures 12
and 13). These were held in by tension at first, but
after they started to wobble I put a strip of double-sided foam tape inside each tube’s rim. I stretched
a piece of canvas around the tubes to form the
belt and then sewed the overlapping ends together
(Figure 14). I’m not much of a tailor, but I think it adds
a bit of Frankensteinian charm to the proceedings
On the software side, we chose to keep things
132 Make: Volume 15