Ultralow Power Battery Operated Data Logger
Introduction
Weather is a condition of the atmosphere. This condition includes Temperature, Humidity, Wind speed and direction, UV index, Solar radiation and so on. Designed Data Logging Device records Temperature and Humidity conditions in uniform interval while consuming lower battery power. Users can monitor recorded weather conditions from Data Logging device wirelessly.
Objective
The objective of this project was to design a Data Logger to log temperature and humidity data over time while the device is smaller in size, battery operated while consuming lower power and easier to retrieve logged data.
Features
- Measures Temperature and Humidity in predefined uniform interval.
- Access the device wirelessly with Wi-Fi and mDNS.
- Collected data can be display in table and graph view from web browser.
- Device system time can be adjusted wirelessly without internet connection.
- Download the collected data to the client device wirelessly.
- Collected data stored in SD card in the device locally.
- Wi-Fi settings, data collecting interval can be configured through a file in SD card.
- Firmware can be updated wirelessly.
- Battery operated low power device.
- Built-in overcharging and over discharging protection.
- Batteries can be charged without removing.
Specifications
Methodology
Measuring both Temperature and Humidity from single sensor is done to decrease battery consumption as it is a battery-operated device. Sensor with lower response time takes smaller time period to take measurements. By powering up the sensor when necessary to take the measurements decreases battery consumption. Sensor turned on and off using MOSFET with external signal from MCU. DHT22 was selected to measure Temperature and Humidity as it has lower response time compared to DHT 21 and DHT 11 sensors. Furthermore, Required Temperature and Humidity measuring range lying on the Measuring Range of DHT22 Sensor and has more accuracy compared to DHT 21 and DHT 11 sensors.
Temperature and Humidity Measurements over time was logged locally in SD Card as it is easier to increase the storage capacity by replacing the SD Card and retrieve the data simply removing the SD Card in device failures. SD Card Module was turned on and off using MOSFET with external signal from MCU to decrease the battery consumption.
ESP32 was selected as MCU as it is a SoC (System on Chip) with inbuilt Wi-Fi and sleep mode functions.
The device has two operating modes. Monitoring Mode and Logging Mode. The Mode can be selected with a toggle switch on the device.
The operation of the Logging Mode is as follows.
The device power on the DHT22 sensor, collects the humidity and temperature measurements and turns off the sensor. After that, the device powers on the SD Card Module and logs the sensor data into SD Card and turns off. Then ESP32 turns off all the Systems on the Chip itself except RTC (Real Time Clock) and ULP Coprocessor. In a predefined interval, ESP32 turns on itself and collects the sensor data and logs it into SD Card.
The operation of Monitoring Mode is as follows.
Logged data on SD Card can be visualized and retrieved easily with any smart device with Wi-Fi capability via Web Server hosted on ESP32 itself with the help of ESP32 Wi-Fi capability. Furthermore, device configurations like Temperature and Humidity measuring interval, device time and firmware update can be done via this Web Server hosted on ESP32.
Power Consumption
Current Consumption
Device in normal operation — 62.5mA
Device in deep sleep — 12mA
Device in deep sleep (After Removing LED) — 10.5mA
DHT11 Sensor 1.25mA
SD Card Module (Idle) — 7mA
SD Card Module (When saving data) — 13.5mA
Power Consumption
Device in normal operation
P = 62.5mA x 5V = 312.5mW
Device in deep sleep
P = 12mA x 5V = 60mW
Device in deep sleep (After Removing LED)
P = 10.5mA x 5V = 52.5mW
DHT11 Sensor 1.25mA
P = 1.25mA x 3.3V = 4.125mW
SD Card Module (Idle)
P = 7mA x 3.3V = 23.1mW
SD Card Module (When saving data) — 13.5mA
P = 13.5mA x 3.3V = 44.55mW
Results
