[DOC] add real-life battery endurance

README.md

@@ -1,9 +1,24 @@
-# 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
+The [esp32-idf](https://docs.espressif.com/projects/esp-idf/en/latest/esp32/get-started/index.html#installation-step-by-step) is needed to compile software for the ESP32.
+The following sections will install to `~/Development/esp32` as an example.
+
 Prepare toolchain (macOS):
 ```
-cd ~/JBeyerstedt-Projekte/
+cd ~/Development/
 mkdir ./esp32
 cd esp32
 curl https://dl.espressif.com/dl/xtensa-esp32-elf-osx-1.22.0-80-g6c4433a-5.2.0.tar.gz -o xtensa-esp32-elf-osx-1.22.0-80-g6c4433a-5.2.0.tar.gz
@@ -11,7 +26,7 @@ tar -xzf xtensa-esp32-elf-osx-1.22.0-80-g6c4433a-5.2.0.tar.gz
 rm xtensa-esp32-elf-osx-1.22.0-80-g6c4433a-5.2.0.tar.gz
 ```
 
-Prepare toolchain (Debian, Ubuntu) (ubuntu devel vm):
+Prepare toolchain (Debian, Ubuntu):
 ```
 sudo apt-get install git wget make libncurses-dev flex bison gperf python python-serial
 
@@ -25,30 +40,23 @@ rm xtensa-esp32-elf-linux64-1.22.0-73-ge28a011-5.2.0.tar.gz
 
 Add to your bash profile, zshrc or other:
 ```
-export PATH=$PATH:$HOME/JBeyerstedt-Projekte/esp32/xtensa-esp32-elf/bin
-export IDF_PATH = $HOME/JBeyerstedt-Projekte/esp32/esp-idf
-```
-or for ubuntu devel vm:
-```
 export PATH=$PATH:$HOME/Development/esp32/xtensa-esp32-elf/bin
 export IDF_PATH = $HOME/Development/esp32/esp-idf
 ```
 
 Install esp-idf:
 ```
+cd ~/Development/esp32
 git clone --recursive https://github.com/espressif/esp-idf.git
 ```
 
 
-## Checkout this project and configure arduino-es32 with esp-idf:
-```
-TODO!!
 
-mkdir -p components && \
-cd components && \
-git clone https://github.com/espressif/arduino-esp32.git arduino && \
-cd arduino && \
-git submodule update --init --recursive && \
+## Checkout this project and configure arduino-esp32 with esp-idf:
+```
+mkdir -p components && cd components
+git clone https://github.com/espressif/arduino-esp32.git arduino && cd arduino
+git submodule update --init --recursive
 cd ../..
 ```
 
@@ -68,3 +76,18 @@ 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) resulted in a slightly better battery life using the voltage regulator.
+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.
+In real-world application, a battery life of about 9 months can be expected (with good WLAN reception).
+
+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;