Voltmeter Clock Project

Overview

The Voltmeter Clock is an Arduino-based project that displays time and environmental data using analog voltmeters. The device uses three voltmeters to show either:

• Time Mode: Hours, minutes, and seconds
• PTH Mode: Pressure, Temperature, and Humidity

The voltmeters are controlled via PWM (Pulse Width Modulation) signals, where the voltage level corresponds to the displayed value. The device features a real-time clock (RTC) for accurate timekeeping and multiple sensors for environmental monitoring.

Hardware Components

Microcontroller

• Arduino (compatible board)

Sensors

1. BMP180 - Barometric pressure and temperature sensor
   • Pressure range: 950-1030 hPa
   • Temperature: Celsius readings

2. DHT22 - Humidity and temperature sensor

   • Humidity range: 0-100% RH
   • Temperature: Fahrenheit readings
3. DS1307 RTC (via uRTCLib) - Real-time clock module
   • Maintains accurate time even when power is off

Display Components

• 3 Analog Voltmeters - Used as display devices
  • Hour voltmeter (PWM pin 9)
  • Minute voltmeter (PWM pin 5)
  • Second voltmeter (PWM pin 6)

Input Components

• Rotary Encoder (Limit Switch) - For time adjustment
  • Pin A: Digital pin 2 (interrupt-enabled)
  • Pin B: Digital pin 3 (interrupt-enabled)
• Button - For mode switching and time adjustment
  • Digital pin 4 (with internal pull-up)

Indicator LEDs

• Hour LED (Pin 8) - Indicates hour display/adjustment
• Minute LED (Pin 10) - Indicates minute display/adjustment
• Second LED (Pin 11) - Indicates second display/adjustment
• PTH LED (Pin 12) - Indicates PTH mode active

Pin Configuration

Software Architecture

Libraries Used

• Arduino.h - Core Arduino functionality
• uRTCLib.h - Real-time clock library for DS1307
• Adafruit_Sensor.h - Sensor abstraction layer
• Adafruit_BMP085_U.h - BMP180 pressure sensor library
• DHT.h - DHT22 humidity sensor library

Key Variables

Display Values

• hrVal, minVal, secVal - PWM values (0-255) for each voltmeter
• displayMode - Current mode (0 = Time, 1 = PTH)

Time Variables

• quarterSecVal - Sub-second PWM adjustment for smooth second hand movement
• currentSec - Current second value for quarter-second tracking

Sensor Data

• pressure - Pressure in hPa (from BMP180)
• temperature - Temperature in °C (from BMP180)
• humidity - Humidity in % RH (from DHT22)
• dhtTemperature - Temperature in °F (from DHT22)

Adjustment Variables

• counter - Rotary encoder counter value
• isAdjustingTime - Flag indicating time adjustment mode
• currentAdjustmentStep - Current adjustment step (0=Hour, 1=Minute, 2=Second)

Functionality

Display Modes

Mode 0: Time Display

The voltmeters display the current time:

• Hour Voltmeter: Shows hours (0-12, 12-hour format)
  • Formula: (hour % 12 + minute / 60.0) * 255.0 / 12
  • Includes fractional hour based on minutes
• Minute Voltmeter: Shows minutes (0-60)
  • Formula: (minute + second / 60.0) * 255.0 / 60
  • Includes fractional minute based on seconds
• Second Voltmeter: Shows seconds (0-60)
  • Formula: map(second, 0, 60, 0, 255) + quarterSecVal
  • Includes quarter-second interpolation for smooth movement

Mode 1: PTH Display (Pressure, Temperature, Humidity)

The voltmeters display environmental data:

• Hour Voltmeter: Pressure (950-1030 hPa mapped to 0-255)
• Minute Voltmeter: Temperature (40-100°F mapped to 0-255)
• Second Voltmeter: Humidity (0-100% RH mapped to 0-255)

Time Adjustment Mode

To adjust the time:

1. Long Press the button (hold for >500ms) to enter adjustment mode
2. The device cycles through three adjustment steps:
   • Step 0: Adjust hours (0-11)
   • Step 1: Adjust minutes (0-59)
   • Step 2: Adjust seconds (0-59)
3. Use the rotary encoder to change values
4. Press the button to confirm and move to the next step
5. After setting seconds, adjustment mode exits automatically

LED Indicators

Normal Operation

• Time Mode (Mode 0):
  • Hour, Minute, Second LEDs: ON
  • PTH LED: OFF
• PTH Mode (Mode 1):
  • Hour, Minute, Second LEDs: OFF
  • PTH LED: ON

Time Adjustment Mode

• The LED corresponding to the current adjustment step blinks (500ms interval)
• Other LEDs are OFF

Rotary Encoder

The rotary encoder uses interrupt-driven quadrature decoding:

• Clockwise rotation: Increments counter
• Counter-clockwise rotation: Decrements counter
• Counter is constrained based on current adjustment step:
  • Hours: 0-11
  • Minutes: 0-59
  • Seconds: 0-59

Quarter-Second Interpolation

For smooth second hand movement, the code implements quarter-second interpolation:

• Divides each second into 4 quarters (0-250ms, 250-500ms, 500-750ms, 750-1000ms)
• Adds incremental PWM values during each quarter
• Provides smooth analog movement between second ticks

Operation Guide

Initial Setup

1. Upload the code to your Arduino board
2. Connect all components according to the pin configuration
3. Power on the device
4. The device will initialize sensors and start displaying time

Normal Operation

Viewing Time

• By default, the device displays time on the three voltmeters
• Hour, Minute, and Second LEDs are lit to indicate time mode
• The second hand moves smoothly with quarter-second interpolation

Viewing Environmental Data

1. Short press the button to switch to PTH mode
2. The PTH LED lights up
3. Voltmeters now display:
   • Pressure (left voltmeter)
   • Temperature (middle voltmeter)
   • Humidity (right voltmeter)
4. Short press again to return to time mode

Adjusting Time

1. Long press the button (hold for more than 0.5 seconds)
2. The Hour LED starts blinking, indicating hour adjustment mode
3. Rotate the encoder to set the desired hour (0-11)
4. Press the button to confirm and move to minute adjustment
5. The Minute LED blinks
6. Rotate the encoder to set minutes (0-59)
7. Press the button to confirm and move to second adjustment
8. The Second LED blinks
9. Rotate the encoder to set seconds (0-59)
10. Press the button to finish adjustment
11. The device returns to normal operation (starts in PTH mode, press button to return to time)

Serial Monitor (Optional)

If debug_println is enabled, the serial monitor (9600 baud) will display:

• Current time (in Time mode)
• Pressure, Temperature, Humidity (in PTH mode)
• Debug information about button presses, encoder movements, etc.

Technical Details

PWM Mapping

Time Display

• Hours: 12-hour format mapped to 0-255 PWM
  • 0 = 12:00 AM/PM
  • 127.5 = 6:00 AM/PM
  • 255 = 12:00 AM/PM (wrap-around)
• Minutes: 0-60 minutes mapped to 0-255 PWM
  • Linear mapping with fractional seconds included
• Seconds: 0-60 seconds mapped to 0-255 PWM
  • Includes quarter-second interpolation for smoothness

PTH Display

• Pressure: 950-1030 hPa → 0-255 PWM
  • Linear mapping
  • Values outside range are constrained
• Temperature: 40-100°F → 0-255 PWM
  • Linear mapping
  • Values outside range are constrained
• Humidity: 0-100% RH → 0-255 PWM
  • Linear mapping
  • Direct percentage to PWM conversion

Sensor Reading Intervals

• Sensors are read continuously in the main loop
• Serial output updates every 500ms (blink interval)
• RTC data is refreshed every loop iteration

Error Handling

• BMP180: Returns -1 for pressure/temperature if read fails
• DHT22: Returns -1 for humidity/temperature if read fails
• Sensor initialization failures halt execution with error message

Troubleshooting

Voltmeters Not Moving

• Check PWM pin connections (9, 5, 6)
• Verify voltmeters are properly calibrated
• Check power supply to voltmeters

Time Not Accurate

• Verify RTC module is connected and powered
• Check I2C connections (SDA/SCL)
• Ensure RTC has backup battery

Sensors Not Reading

• BMP180: Check I2C connections and power
• DHT22: Verify pin 7 connection and power
• Check sensor wiring and pull-up resistors

Button Not Responding

• Verify button is connected to pin 4
• Check internal pull-up is working
• Test button continuity

Rotary Encoder Not Working

• Verify pins 2 and 3 connections
• Check interrupt functionality
• Ensure encoder has proper power and ground

LEDs Not Indicating

• Check LED pin connections (8, 10, 11, 12)
• Verify LED polarity and current-limiting resistors
• Test LED pins individually

Future Enhancements

The code includes a placeholder for brightness adjustment (step 3 in adjustment mode), but this feature is not yet implemented. The maxCounter is set to 20 for this step, but the functionality is not active.

Code Structure

Main Functions

• setup() - Initializes pins, sensors, interrupts, and serial communication
• loop() - Main program loop handling button input, time adjustment, and display updates
• updateTimeDisplay() - Calculates and outputs PWM values for time display
• updatePTH() - Calculates and outputs PWM values for environmental data
• adjustTime() - Handles time adjustment mode logic
• displayAdjustment() - Shows current adjustment value on voltmeters
• updateEncoderA() / updateEncoderB() - Interrupt handlers for rotary encoder
• readPressure() - Reads BMP180 sensor data
• readHumidity() - Reads DHT22 sensor data
• toggleDisplayMode() - Switches between time and PTH modes
• controlLEDsBasedOnDisplayMode() - Controls LED indicators
• blinkPin() - Blinks LED at specified interval
• handleQuarterSec() - Implements quarter-second interpolation
• blinkDisplaySerial() - Outputs serial data at intervals

License

This project is provided as-is for educational and personal use.

Author Notes

This voltmeter clock project combines analog display aesthetics with modern sensor technology, creating a unique timepiece that also serves as an environmental monitoring station. The smooth analog movement of the voltmeters provides a classic watch-like experience while displaying both time and real-time environmental conditions.