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arduino/README.md

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+# Arduino IoT device
+
+A simple Arduino UNO sketch is provided in the `arduino/tempLightSensor` folder.
+The sketch reads temperature and light from sensors. 
+
+The simple schematic is:
+
+![tempLightSensor](./tempLightSensor/tempLightSensor.svg)
+
+The sketch does require an Ethernet shield and a bunch of libraries which are
+available as git submodules under `arduino/libraries`.
+
+```bash
+git submodule update --init
+```
+
+Be advised that some libraries (notably the `NTP` one) have been customized.
+
+An `ESP32` board (or similar Arduino) may be used, with some adaptions, too.
+
+## EEPROM
+
+Configuration parameters are stored and retrieved from the `EEPROM`.
+An helper sketch to update the `EEPROM` is available under
+`arduino/eeprom_prog`.
+
+The data stored in the `EEPROM` is:
+
+```c
+// Ethernet MAC address
+const byte mac[6];
+
+// Device serial number
+const char serial[];
+
+// IoT platform address and port
+struct netConfig {
+  IPAddress address;
+  unsigned int port;
+};
+
+```
+
+The `EEPROM` can be completely erased setting the `ERASE_FIRST` macro to `1`.
+
+```c
+#define ERASE_FIRST 0
+```
+
+## Firmware options
+
+The following macros are available in the firmware (to be set at compile time):
+
+```c
+#define DEBUG_TO_SERIAL 1  // debug on serial port
+#define USE_MQTT 1         // use mqtt protocol instead of http post
+#define USE_INTERNAL_NTP 0 // use default ntp server or the internal one
+```