This is a micropython project for an ESP8266 which reads the temperature, then dumps it to an MQTT broker. It is designed to run off batteries - in my case, direct to some 18650 Li-ion cells. It uses a DS18B20 temperature sensor, connected VCC->Pin 13, GND->Pin 14, Data->Pin 12 (this is easy to change).
I'll upload a schematic and photos soon.
Features include:
- Reads temperature, dumps to MQTT, then deep sleeps for a defined amount of time.
- Tries to connect to network for a little while, but shuts back down to deep sleep if can't connect.
- When battery voltage drops below a certain amount, attempts to send a message, then deep sleeps indefinitely to prevent draining battery too low
- Checks for a stop signal on MQTT. If received, goes into webrepl mode to allow for remote maintenance/updates
Usage:
- Flash micropython onto the device
- create secrets.py, and define ESSID and PASSWD in that file for your network configuration
- edit config.py to suit (particularly MQTT_SERVER)
- copy all files across using your method of choice (webrepl is one option)
- in a REPL, run
import set_adc_vcc; set_adc_vcc.set_adc_vcc()- this configures the internal flash to use the ADC to measure the VCC voltage rather than from the external pin. - measure battery voltage using a voltmeter
- start the device - be ready to press Ctrl-C if connected by serial, or else push a retained MQTT message to your broker e.g.
mosquitto_pub -h localhost -r -t stop -m "esp-01"then connect via webrepl - determine correct VCC_CALIBRATION_OFFSET_MV, change this in the config.py file, and upload config.py again.