update influxdb domain name, tweak battery level thresholds

README.md

@@ -1,7 +1,16 @@
-# Readme
+# ESP32-based Environmental Sensor
 Author: Jannik Beyerstedt  
 **license:** GNU GPL v3
 
+A simple temperature and humidity sensor node using an ESP32 and a Si7021 sensor element running of a 18650 LiIon battery cell.
+The sensor outputs the data to an influxDB instance, which must be reachable via HTTP.
+
+To save energy, we use a lower CPU frequency.
+But this requires compiling the core framework again with the changed settings (see below).
+
+This repository contains the code running on the ESP32, as well as the PCB and case design.
+
+
 
 ## Dependencies
 Prepare toolchain (macOS):
@@ -43,7 +52,8 @@ git clone --recursive https://github.com/espressif/esp-idf.git
 ```
 
 
-## Checkout this project and configure arduino-es32 with esp-idf:
+
+## Checkout this project and configure arduino-esp32 with esp-idf:
 ```
 TODO!!
 
@@ -71,3 +81,17 @@ make all
 make flash
 ```
 You would probably have to adapt the `UPLOAD_PORT` in the `Makefile` or set it via an environment variable.
+
+
+
+## Battery Life
+The hardware was designed with two options to drop the battery voltage to a level, which can be fed to the ESP32: A voltage regulator or a simple diode.
+
+A test with increased data rate (for a shorter test duration) showed, that the voltage regulator leads to a slight battery life benefit.
+Using a measurement interval of 30 seconds and a WiFi connection interval of 3 minutes, the 2500mAh LiIon (3.7V) battery lasted 30 days with the diode and 36 days using the voltage regulator.
+
+The selected voltage regulator has a quite low drop-out voltage and more importantly a low leaking current during the deep-sleep phases, which have a very low current needed by the ESP32.
+In comparison a diode has no leaking current at all, but a more or less fixed voltage drop.
+
+The benefit of the voltage regulator is, that the battery voltage range can be exploited further than what can be done with the diode.
+The lowest operational battery level was 3.2 V using the diode and 2.8 V using the voltage regulator.

main/esp32-sensornode_main.cpp

@@ -31,11 +31,11 @@
 #define BOARD 4 /* IMPORTANT: select one of the BOARD_* types */
 #endif
 
-#define DB_HOSTNAME "ursaminor.fra80"
+#define DB_HOSTNAME "influx-iot.fra80"
 #define DB_PASSWD "c2Vuc29yczpTZW5zb3JzLXcuaW5mbHV4QGhvbWU"  // BasicAuth String
 
 #if BOARD == BOARD_ESP32
-#define BATT_FULL 3800    // 4.3V Battery
+#define BATT_FULL 3700    // 4.2V Battery
 #define BATT_CUTOFF 2500  // 2.8V Battery
 #else
 #error "unsupported board chosen"
@@ -68,9 +68,9 @@ String         serviceUri         = "/write?db=test";
 #endif
 
 /* GLOBAL VARIABLES */
-const uint16_t wlanConnectCheckInterval  = 250;    // milli seconds: poll wifi.state after wifi.begin()
-const uint16_t wlanConnectTimeout        = 15000;  // milli seconds
-RTC_DATA_ATTR uint8_t wlanConnectFailCnt = 0;
+const uint16_t        wlanConnectCheckInterval = 250;    // milli seconds: poll wifi.state after wifi.begin()
+const uint16_t        wlanConnectTimeout       = 15000;  // milli seconds
+RTC_DATA_ATTR uint8_t wlanConnectFailCnt       = 0;
 
 Si7021 si7021 = Si7021();
 float  temp   = 0.0;