PROJECTS: Arduino Fingerprint Sensor Lock
5. WIRE THE RELAY TERMINALS
The relay's middle screw terminal is the COM
(common contact) that will be connected to the
second terminal when the signal pin is set to
HIGH. Connect the positive wire from the solenoid
door lock to this COM terminal.
The second terminal used is NO (normally
open); this represents the status of the terminals
when there is no signal coming from D5. Attach a
relatively long wire to be routed later (Figure
F
).
6. ADD THE 9V BATTERY
Using the wires from Step 3, solder Arduino GND
to the battery connector’s negative terminal,
and solder the flip switch pin to the battery
connector’s positive terminal (Figure
G
).
7. ADD THE BARREL CONNECTOR
Connect the negative wire from the solenoid to
the negative terminal of the barrel connector.
Finally, connect the NO (normally open) wire
from Step 5 to the positive terminal of the barrel
connector (Figure
H
).
8. SET UP THE FINGERPRINT SENSOR
The Adafruit Fingerprint Sensor setup process
can be found at learn.adafruit.com/adafruit-
optical-fingerprint-sensor. After you’ve added
(“enrolled”) the desired fingerprints, you need to
add some lines to the Adafruit sample code.
2. SOLDER THE RELAY PINS
Following Figures
B
and
C
, solder three wires
to connect the relay control pins:
• Signal pin (S) on the relay to digital pin 5 (D5) on
the Arduino Nano
• Positive pin (+) on relay to 5V on Arduino Nano
• Negative pin (–) on relay to ground (GND) on
Arduino Nano
3. ADD THE FLIP SWITCH
Solder two lead wires to the micro switch pins as
shown (Figure
D
). Use appropriate heat-shrink
tubing where there may be wire exposure.
Solder one wire to voltage input (VIN) on the
Arduino Nano. Leave the second wire to be
connected to the battery later (in Step 6).
Also add a ground wire to any GND pin on the
Arduino Nano. (Keep this wire long, as it will go to
the battery too.)
4. CONNECT THE SENSOR
We only need to use four of the six available pins
on this fingerprint sensor (Figure
E
): 5V (red),
GND (black), Tx (green), and Rx (white). Solder
these as follows:
• 5V to the 5V pin on the Arduino Nano
• GND to any GND pin on Arduino Nano
• Tx to the D2 pin on Arduino Nano
• Rx to the D3 pin on Arduino Nano
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