Clock, Alarm, GPS, Noise Generator, and Everything Else: An All-in-One Arduino Device

Project Motivation

The project started with studying the effect of white and pink noise on falling asleep. I tested the effect and discovered that white noise makes it harder to concentrate. Instead of off-the-shelf solutions (mobile apps, children's devices), I decided to build my own device with a microcontroller for flexible volume and duration control.

Technical Implementation

Main components:

• Arduino Nano with ATmega328P microchip
• RTC (Real-Time Clock) PCA2129T for timekeeping
• LCD display 128x64 with green backlight
• Speaker for sound playback
• GPS module GeoS-5M
• Temperature sensor LM75
• Digital potentiometer AD5241BRZ10
• Level converter RS0302YH8
• Voltage regulator RT9193-18GB for GPS power supply

White Noise Generator

Initial attempts at simply outputting pseudorandom values proved unsuccessful. I found a working Stenzel algorithm using a Linear Feedback Shift Register (LFSR) and FIR filter for generating high-quality pink noise.

The code includes:

• A TIMER2_OVF interrupt handler
• A stenzel_pink_sample() function for sample generation
• Bit inversion lookup tables for optimization

The algorithm generates a pseudo-random sequence through an LFSR, then applies a FIR filter to shape the white noise spectrum into a pink noise (1/f) characteristic. The output is sent through a digital potentiometer (AD5241BRZ10) to control volume, then to a small speaker. The timer interrupt runs at a fixed sample rate, ensuring consistent audio output regardless of main loop activity.

Interface and Controls

Display functionality:

• Current time display (without seconds)
• Noise generator activity visualization via a progress bar
• Countdown timer
• Temperature reading in the lower left corner
• Alarm status in the lower right corner

Control with four buttons:

• Button 1: Turn noise generator on/off
• Button 2: Enter settings mode
• Buttons 3-4: Change selected parameters

Available settings:

• Date and time
• Noise playback duration
• Volume level (via digital potentiometer)
• Backlight mode (On/Off/Auto with photoresistor)
• Temperature reading correction
• Alarm configuration

GPS Functionality

I integrated the GeoS-5M module for automatic time setting. When you simultaneously press the power button and the generator button, a waiting screen appears showing it's expecting data from the GPS receiver. This feature is still under development.

Alarm Code

if((Alarm_EN == 1) && (now.hour() == Alarm_H) && (now.minute() == Alarm_M)){
  tone(NOISE_PIN, 1000, 50);
}

The alarm emits a 1000 Hz tone for 50 milliseconds at the set time.

Circuit Design Decisions

• All GPIO pins on the microcontroller are occupied; ADC inputs were used for additional buttons
• The built-in LDO regulator was desoldered from the Arduino Nano board
• All buttons are duplicated to a separate connector
• The display is mounted on pin headers; the Arduino is soldered directly

Hardware Testing

The ATmega328P's built-in temperature sensor proved inaccurate (deviation up to 15 degrees Celsius). The LM75 sensor was chosen as a more reliable solution.

After powering on, the device worked immediately — only contrast calibration was needed.

Future Plans

I plan to create a new compact board with USB-C power, better connector placement, complete the GPS implementation, and write about the enclosure and test results in the next article.