11

TUTORIAL

Monkey skull treasure bowl

CAPACITIVE SENSING

The capacitive sensors on the Gemma work by

charging and discharging the output pins and

measuring the voltage. The pins have a small amount

of capacitance and the microcontroller is sensitive

enough to measure this. When a person is very

near to the sensor, they affect the circuit by acting

as a second capacitor. This means that when the

microcontroller charges and discharges the pin, it

will see a change in behaviour and know that it has

been touched.

Above

LEDs only work if the

current flows from

anode to cathode

Below

Schematic

LED. Make a note of which wire connects to the

anode of the LED.

Use a bradawl or skewer to make a hole in the

back of the eye sockets and into the cardboard box.

Pass the wires through the holes and out of the box.

Crimp a resistor to one of the LED wires.

YOU’VE GOT THE TOUCH

The sensor for the touch is formed from the

screening from the screened wire. Remove the

outer plastic cover of the screened wire and slide

the braided screen off the wires. Flatten the braid

and form into a loop to fit around the rim of the

bowl. Twist the ends together and crimp to a

wire. Make a hole from the bowl through to the

electronics box and pass the wire though. The braid

can then be attached to the bowl with hot glue.

Strip the ends of the wire and wrap around an

M2.5 bolt, and twist the end to form a loop. Form a

loop on the end of each resistor. Bolt one LED anode

wire to the D0 connection on the Gemma, and the

other anode wire to D2. The cathode wires should

be bolted to the 0 V connector. Bolt the sensor wire

to the A0 connection.

BRAIN POWER

The Gemma M0 uses an ATSAMD21E18 processor,

and this is powerful enough to run a subset of the

Python language called CircuitPython. Combined

with the provided libraries, this means we can build

this kind of project with just a few lines of code.

import time

import board

import touchio

from digitalio import DigitalInOut, Direction

We start with instructions to use the libraries for

time, board, and touchio. For the digitalio import

instruction, we’ve just picked the items we need.