A fingerprint-activated nightstand lock built on an Arduino Uno-compatible controller. A capacitive fingerprint sensor authenticates the user, and on a successful match the controller drives a relay that releases a locking solenoid.
This project was completed for Engineering Design and Project Management at the University of Houston-Clear Lake (UHCL) during Fall 2025.
The completed system was installed on a nightstand for the final demonstration and remains in use there without any reported issues.
Traditional safety boxes rely on keys or passcodes that are easy to lose, and off-the-shelf biometric boxes are expensive. This project is a low-cost alternative that demonstrates embedded control, sensor integration, and secure storage design.
Team: Abigail Duran, Ethan Wells, Alexis Perez
| Path | Description |
|---|---|
BiometricLockingBox/BiometricLockingBox.ino |
Arduino sketch: matching loop that unlocks the solenoid on a fingerprint match. Adapted from the Adafruit fingerprint example. |
partslist.md |
Complete from-scratch parts list, purchase details, and source links. |
docs/ |
Wiring diagram and project diagrams (see Wiring and Project documentation). |
docs/Fingerprint Sensor Box rework.SLDPRT |
SolidWorks source model for the 3D-printed fingerprint-sensor cover. |
BIOMETRIC SCANNER BOX (1).pptx |
Full project proposal deck. |
Project Analysis Paper.pdf |
Project analysis paper. |
LICENSE |
BSD 3-Clause license. |
- ELEGOO UNO R3-compatible controller
- Adafruit R503 3.3 V capacitive fingerprint sensor
- Relay module
- Locking solenoid
- 12 V DC power supply
- Breadboard and jumper wires
- Custom 3D-printed fingerprint-sensor cover
The system is mounted to an existing nightstand; a separate enclosure is not part of the completed installation or bill of materials.
The installed sensor emits light while it is idle and waiting for a fingerprint. A
custom 3D-printed cover shields that light during normal use. The editable SolidWorks
model is available at
docs/Fingerprint Sensor Box rework.SLDPRT.
The 12 V adapter powers both the Arduino and the solenoid. The solenoid is switched through the relay — never driven directly from an Arduino pin — and all grounds are common.
Fingerprint sensor → Arduino Uno
| Sensor pin | Arduino pin |
|---|---|
| GND | GND |
| RX | D3 |
| TX | D2 |
| 3V3 | 3.3 V |
| T-OUT | do not connect |
| T-3V3 | do not connect |
The sketch talks to the sensor over SoftwareSerial on D2/D3. On a board with a
spare hardware UART (Leonardo, M0, Mega, etc.) it automatically uses Serial1
instead.
Arduino outputs
| Arduino pin | Connection |
|---|---|
| D4 | Relay control for the locking solenoid (active LOW) |
| D8 | Spare output, driven HIGH at boot |
| D13 | Spare output / onboard LED, driven HIGH at boot |
- Arduino IDE
- Arduino Uno Rev3 using the Arduino AVR Boards core 1.8.8
- Adafruit Fingerprint Sensor Library 2.1.4 (install via Tools → Manage Libraries… → "Adafruit Fingerprint Sensor Library")
These pinned versions form the repository's reproducible compile baseline. The exact Arduino IDE and AVR core versions used for the Fall 2025 prototype were not recorded; the compile workflow installs Adafruit Fingerprint Sensor Library 2.1.4 explicitly.
| Port | Baud |
|---|---|
| USB serial monitor | 9600 |
| Fingerprint sensor | 57600 |
- Wire the hardware as described above.
- Install the Adafruit Fingerprint Sensor Library in the Arduino IDE.
- Enroll fingerprints first. This sketch only matches against templates already stored on the sensor; it does not enroll them. Open File → Examples → Adafruit Fingerprint Sensor Library → enroll, upload it, and follow the serial prompts to store each user's print. The design target is at least 5 enrolled fingerprints.
- Open
BiometricLockingBox/BiometricLockingBox.ino, select your board and port, and upload. - Open the Serial Monitor at 9600 baud. On boot the sketch prints the sensor parameters and the number of stored templates, then waits for a finger.
Adafruit finger detect test
Found fingerprint sensor!
Reading sensor parameters
Status: 0x0
...
Waiting for valid finger...
Sensor contains 5 templates
Image taken
Image converted
Found a print match!
Found ID #1 with confidence of 142
If the sensor is not detected the sketch prints
Did not find fingerprint sensor :( and halts — check wiring, the TX/RX swap,
and that the sensor is powered.
loop() calls getFingerprintID() every 50 ms:
finger.getImage()— capture an image. Returns immediately when no finger is present.finger.image2Tz()— convert the image into a feature template.finger.fingerSearch()— search the stored templates for a match.- On a match, pin 4 is pulled LOW for 3 seconds to energize the relay and release the solenoid, then returned HIGH to re-lock.
The unlock window was set to 3 seconds during integration.
Every failure path prints a human-readable reason to the serial monitor (imaging error, image too messy, communication error, no match, etc.).
getFingerprintIDez() is an unused helper from the Adafruit example that performs
the same lookup with fingerFastSearch() and no serial chatter.
- Easy to install
- Low cost
- Low power
- Fast
- Correctly identify an enrolled user with ≥95% accuracy
- Solenoid responds within 1 second of verification
- Powered by no more than 12 V DC
- Operates continuously for at least 8 hours
- Nightstand re-locks automatically after the 3-second unlock window
- Stores and checks at least 5 different fingerprints
Diagrams exported from the project proposal deck. The proposal and analysis paper are static historical documents and may describe earlier design values; the sketch, README, and parts list document the final maintained installation.
User requirements weighed against the engineering requirements that satisfy them.
The system broken into three branches — biometric input, system control and logic, and locking mechanism actuation.
Task dependencies across the 5-week schedule. Both A→B→D→F and A→C→E→F are critical paths, so there is no float time.
| Task | Description | Duration |
|---|---|---|
| A | Schematic and bill of materials | 1 week |
| B | Hardware setup, build prototype | 1 week |
| C | Software development, integrate fingerprint library, confirm identification and accuracy | 1 week |
| D | System integration, add timer to locking solenoid, and mount onto the nightstand | 1 week |
| E | Testing and optimization, run tests to meet all engineering requirements | 1 week |
| F | Finalization, full demo run, prepare final report and rehearse presentation | 1 week |
Total: 35 days (5 weeks).
BSD 3-Clause — see LICENSE.
Fingerprint handling is adapted from the Adafruit Fingerprint Sensor Library example by Limor Fried / Ladyada, Adafruit Industries, which is BSD licensed. The upstream attribution is retained in the sketch header.