Android Apps for Builds

Your old phone is already packed with accelerometers, gyroscopes, magnetometers, barometers, cameras, and microphones. These apps unlock them for builds.

A phone you already own (or a $30 used phone from eBay) has more sensors than most microcontroller setups. These apps turn a phone into a lab instrument, controller, camera system, or data logger — no soldering required.

Phyphox

What it does: The single best physics sensor app. Built by RWTH Aachen University. Gives you direct access to every sensor on your phone with real-time graphs, data export (CSV, Excel), and remote access via a built-in web server (control the phone from your laptop browser).

Sensors accessible: Accelerometer, gyroscope, magnetometer, barometer, light sensor, proximity sensor, GPS, microphone (with FFT, autocorrelation, and spectrum analysis).

Key features:

• Real-time graphing of all sensor data
• Data export to CSV for analysis in Python/Excel
• Remote access — control the phone from any device on the same WiFi network
• Custom experiments — chain multiple sensors and processing steps
• Acoustic stopwatch (measures time between sounds)
• Doppler effect measurement
• Pendulum period analysis

Used in builds:

• Phone Sensor Network — multi-phone sensor logging
• Earthquake Detector — accelerometer data capture
• Calibration and testing across many builds

Free/Paid: Completely free, no ads, open source.

Platform: Android and iOS. Google Play link

Spectroid

What it does: Real-time audio spectrum analyzer. Shows a scrolling spectrogram (frequency vs time) with color-coded intensity. Excellent for visualizing sound patterns, finding resonant frequencies, and diagnosing audio issues.

Key features:

• Real-time scrolling spectrogram
• Frequency range up to 22kHz (limited by phone microphone)
• Peak frequency display
• Adjustable FFT size and window function
• Waterfall display mode

Used in builds:

• Arduino Guitar Pedal — verifying audio effects
• MIDI Stepper Organ — tuning stepper frequencies
• Hard Drive Speaker — testing frequency response
• Any build that produces or modifies sound

Free/Paid: Free, with ads. No paid version needed — the free version is fully functional.

Platform: Android. Google Play link

Physics Toolbox Suite

What it does: Multi-sensor data logger that records and exports data from all phone sensors simultaneously. More focused on data logging and export than Phyphox's experiment-building approach.

Key features:

• Simultaneous recording from multiple sensors
• CSV data export
• Real-time multi-axis graphs
• GPS logger with altitude and speed
• Sound level meter (dB)
• Tone generator (for testing speakers and microphones)
• Stroboscope function

Used in builds:

• Phone Sensor Network — data logging
• Earthquake Detector — vibration recording
• Testing and calibration across builds

Free/Paid: Free version available. Pro version ($2.99) removes ads and adds multi-sensor simultaneous recording.

Platform: Android and iOS. Google Play link

FrequenSee

What it does: Audio frequency visualizer with a clean, readable interface. Shows real-time frequency spectrum as a bar graph or line graph. Simpler than Spectroid but easier to read at a glance.

Key features:

• Real-time frequency spectrum display
• Peak hold (shows the highest level reached at each frequency)
• Adjustable frequency range and resolution
• Clean, high-contrast display
• dB scale with adjustable range

Used in builds:

• Plasma Speaker — verifying audio reproduction quality
• Audio testing for any build with speakers or microphones
• Finding resonant frequencies of mechanical structures

Free/Paid: Free.

Platform: Android. Google Play link

IP Webcam

What it does: Turns your phone into a network-accessible IP camera. Streams video (and audio) over WiFi that can be captured by Python scripts (OpenCV), VLC, or any RTSP/MJPEG client. Effectively gives you a free wireless camera for any build.

Key features:

• MJPEG and RTSP video streaming over WiFi
• Accessible via browser (http://phone-ip:8080)
• OpenCV-compatible URL: http://phone-ip:8080/video
• Motion detection with recording
• Audio streaming
• Flash/torch control via API
• Autofocus control
• Sensor data overlay (accelerometer, GPS) on video

Used in builds:

• Face Tracking Laser — video source for OpenCV (alternative to USB webcam)
• AI Photo Booth — camera source
• AI Doorbell — camera feed
• ESP32-CAM Security — alternative/additional camera
• Any build needing a wireless camera feed

Free/Paid: Free version fully functional. Pro version ($3.99) adds features like cloud streaming and tasker integration.

Platform: Android. Google Play link

Python integration example:

import cv2
cap = cv2.VideoCapture("http://192.168.1.100:8080/video")
while True:
    ret, frame = cap.read()
    if ret:
        cv2.imshow("Phone Camera", frame)
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

Sensors Multitool

What it does: Raw sensor access with numerical readouts. Shows the exact values from every sensor on your phone in real time — no graphs, no processing, just raw numbers. Useful for verifying sensor functionality and reading precise values.

Key features:

• Lists every sensor on your phone with model numbers and specs
• Real-time numerical readout of all sensor axes
• Magnetic field strength in microtesla (useful for magnet testing)
• Barometric pressure in hPa
• Light level in lux
• Proximity sensor distance
• Sensor specifications (range, resolution, power draw)

Used in builds:

• EMF Ghost Detector — comparing phone magnetometer readings with Arduino EMF sensor
• Verifying sensor calibration and functionality
• Quick magnetic field measurements (testing salvaged magnets)

Free/Paid: Free, with ads.

Platform: Android. Google Play link

Arduino Bluetooth Controller

What it does: Sends commands to an Arduino or ESP32 via Bluetooth. Provides virtual buttons, joystick, slider, and terminal interfaces. The fastest way to add wireless control to a microcontroller build without writing a custom app.

Key features:

• Button mode — up to 6 customizable buttons, each sends a character or string
• Joystick mode — sends X/Y coordinates continuously
• Slider mode — sends a value from 0-255
• Terminal mode — send and receive text strings
• Accelerometer mode — sends phone tilt data
• Voice control mode — speech-to-text commands

Used in builds:

• ESP32 Mesh Walkie-Talkie — configuration interface
• Nerf Sentry Turret — manual override control
• Electric Skateboard — configuration and diagnostics
• Any Arduino/ESP32 build needing wireless control

Free/Paid: Free version supports basic modes. Pro version ($1.99) adds more buttons and features.

Platform: Android. Google Play link

Quick Reference Table

Tips for Using Phones in Builds

1. Use an old phone. Dedicate a used phone to your build rather than risking your daily driver. A used Android phone with working sensors costs $20-30 on eBay.

2. Keep the phone plugged in. For builds that run continuously (cameras, sensor networks), power the phone via USB to prevent battery drain. Disable battery optimization for the app.

3. Lock the screen on. Many apps stop streaming or logging when the screen turns off. Use a "Stay Alive" or "Caffeine" app, or enable Developer Options > Stay Awake (while charging).

4. Connect to local WiFi. For IP Webcam and Phyphox remote access, the phone and your computer/Pi must be on the same WiFi network. Use the phone's IP address (Settings > WiFi > tap your network > IP address).

5. Disable notifications. Notifications can interrupt apps and cause data gaps. Use Do Not Disturb mode during data collection.