bolukan/low-energy-bme280-sensor

Low Energy BME280 Sensor using rtc memory and MQTT

Low Energy Sensor Logger - to MQTT broker

This project combines a bare ESP8266, a LiFePo4 battery and a BME280 sensor. It reads sensor data more frequently than connecting to WiFi and transmitting the data. Limiting WiFi connections, which takes 6 seconds and consumes more than 100mA, will save the battery. However the downside is the readings will become available on the server with delay.

Data is sent by mqtt messages to a Mqtt broker. It also sends data on the battery voltage and can be configured to send a special action message if the voltage passes a specific treshold.

This is a project with my rtcmem library, a wrapper for the ESP8266 RTC memory. The rtc library supports the strategy to temporary store sensor readings in the rtc memory which survives deepsleep. The rtcmem can work with variable structs, which will depend on which sensor is used.

This project uses a modified BME280 library to identify the used sensor. The modified library exposes the calibration data. The calibration data is used to calculate a crc32 checksum which is used as identifier.

Discussion

Please help me and contribute this development:

• Measuring energy use
• Suggesting improvements
• Suggesting use cases

Latest stable release: not yet available

Pins

ESP8266 ESP12F on a breakout board + BME280

ESP8266	BME280	LiFePo4
REST - GPIO16
ADC
CH_PD (10K VCC)
GPIO16 - REST
GPIO14
GPIO12
GPIO13
VCC	VCC	PLUS
TXD
RXD
GPIO5	SCL
GPIO4	SDA
GPIO0
GPIO2
GPIO15-10K-GND
GND	GND	MIN

low-energy-bme280-sensor's Issues

Reading spikes due to wifi connection

Of each set readings, the eldest reading is substantially lower for the temperature and pressure.

Further analysis showed a reading from the bme280 returns the last reading and initiates a new one, which will be returned the next time a reading is requested.
The eldest reading is initiated the same time as a set of readings was sent. The presumption is the wifi connection disturbes the reading through radiation or power consumption (capacitators are used).

The proposed solution is to initiate the reading next to closing the wifi connection and to have a little pause (50ms) between the end of the wifi connection and the start of the reading.