ESP_DeepSleepSensor

Code for an ESP32 based sensor using any kind of analog sensor. ESP is going to deep sleep between the sensor measurements. The measured data are transmitted to a MQTT broker and with MQTT the sleep interval can also be configured. The maximum sleep time is set to 3600 seconds, the default sleep time is configured to 300s. So if the broker sets invalid data (such as values that cannot be casted or invalid values), the default sleep time is applied. The sleep time is stored persistent in memory (NVS)

Required hardware / software

• ESP32.
• Some kind of sensor
• MQTT broker

Analog input of the sensor is currently hard coded to analog input 0 Digital output for triggering the sensor is currently hard coded to output 26

When the ESP runs longer than 30mins, it will automatically reboot. This resolves problems if the ESP is in an "unwanted" state, or the ESP accidentally started AP/WEBSERVER.

Required libraries

#include "PubSubClient.h" // tested with version 2.7
#include "ESPAsyncWebServer.h" //tested with version 1.2.3

MQTT message format publish

The topic can be selected freely in the configuration interface The topic for publishing will be extended by "/State". e.g. if you configure Home/MyGardenSensor the state message will be posted to Home/MyGardenSensor/State

The message payload is a JSON formatted string

{
    "state" : "ON|OFF|SLEEP|CONFIG", 
    "value" : "%d", 
    "SleepTime" : "%d",
    "SignalQuality": "%d"
}

state state of the ESP. ON --> running, OFF --> when performing a soft reset or within last will, SLEEP --> when in deep sleep mode value is the raw sensor value. Calibration (e.g. what is moist, what is dry) needs to be done on the other system that processes the sensor readings SleepTime is the amount of seconds that the ESP is currently going to sleep.

Changing the sleep time

The MQTT client automatically subscribes to <configured_topic>/SleepTime for changing the time in seconds for which the ESP should go into deep sleep. Maximum value is 3600s. Any value outside of 0...3600s will fallback to

/**
 * The default sleep time in [s]
 */ 
#define DEF_TIME_TO_SLEEP  5*60 

Change operation mode

The MQTT client automatically subscribes to <configured_topic>/Mode. The following modes are possible

Command	Description
AP	ESP starts as an access point with the IP 192.168.1.4 and starts the webserver for configuration
CONFIG	ESP starts only the webserver for configuration

Since during normal operation the ESP is in deep sleep quite often, those messages must be retained. After recieving an message, an empty payload is automatically sent to this topic in order to delete the retained messages. Otherwise the broker would still send the ESP into CONFIG or AP mode until something else changes the payload of the retained message.

Webserver

The configuration page of the webserver is being read from SPIFFS. Therefore the data folder from this repository must be uploaded to the ESPs file system. The Webserver listens to port 80. After applying the configuration in the webserver, the ESP is restarted When the webserver was started without AP mode (e.g. if the MQTT broker sporadically was offline) the MQTT connection is checked each 5 minutes. A successful MQTT connection will then restart the ESP.

Acces point mode

In AP mode, the ESP creates a WLAN with the SSID ESP32-DeepSleepSensor. No credentials are required. The IP of the ESP is 192.168.4.1

Statemachine

STATE	CONDITION	NEXT STATE	DESCRIPTION
START	(none)	READ_CONFIG	Boot state
READ_CONFIG	configuration OK	CONNECT_WIFI	If configuration parameter are OK, try to connect to WiFi
READ_CONFIG	WiFi parameter missing	START_AP	Starts the ESP in access point mode
READ_CONFIG	MQTT parameter missing	START_WEBSERVER	Start webserver for configuration
CONNECT_WIFI	connection successful	CONNECT_MQTT	Try to connect to MQTT if WiFi connection was successful
CONNECT_WIFI	connection failed	START_AP	Starts the ESP in access point mode if no WiFi connection could be established
CONNECT_MQTT	connection succesful	OPERATIONAL	After MQTT connection switch to normal operation
CONNECT_MQTT	connection failed	START_WEBSERVER	Start webserver for configuration
START_AP	(none)	START_WEBSERVER	after starting in AP mode, the webserver is started for configuration
START_WEBSERVER	(none)	WEBSERVER_RUNNING	Webserver is running
OPERATION	(none)	DEEP_SLEEP	A MQTT message with the status and the sensor readings is published in this state. Afterwards, ESP is being put into deep sleep
DEEP_SLEEP	(none)	(none)	sleeping. A state message is published before ESP goes to sleep

If the configuration is OK and connection to WiFi and MQTT is successful, a normal state transition looks like the following START → READ_CONFIG → CONNECT_WIFI → CONNECT_MQTT → OPERATION → DEEP_SLEEP