added gatt service info

README.md

@@ -1,3 +1,41 @@
 # teng-arduino
-Measure teng output with an arduino
+Measure analog signal using an Arduino and Bluetooth communication.
+This program was written (and tested) for the **Arduino RP2040 Connect**.
+
+[https://github.com/MatthiasQuintern/m-teng] has a backend that can connect to the Arduino.
+
+## Configuration
+See `settings.hpp` for which pin needs to be connected.
+The program uses 3 leds for displaying device status, however these are optional.
+
+## Installation
+```
+git clone https://github.com/MatthiasQuintern/teng-arduino
+arduino-cli compile --profile nanorp
+arduino-cli upload --profile nanorp
+```
+
+## Communication via Bluetooth
+The Arduino will advertise a Bluetooth Low Energy service which can be used to interact with the device. 
+
+Service UUID: `00010000-9a74-4b30-9361-4a16ec09930f`
+0. status (`uint8_t`, `rn`): `00010001-9a74-4b30-9361-4a16ec09930f`
+    - `0`: **ERROR**: error occured: invalid command received, can not advertise Bluetooth service, etc.
+    - `1`: **BUSY**
+    - `2`: **WAIT_CONNECT**: waiting for Bluetooth connection
+    - `3`: **CONNECTED**: connected, waiting for command
+    - `4`: **MEASURING**: connected, measurement running
+1. command (`uint8_t`, `rw`): `00010002-9a74-4b30-9361-4a16ec09930f`
+    send a command to the arduino:
+    - `0` - **STOP**: stop active measurements
+    - `1` - **MEASURE_COUNT**: measure *count* measurements with *interval* *see `count` and `interva` below*
+    - `2` - **MEASURE**: measure with *interval* until interrupted *see `count` below*
+2. reading (`uint16_t` `rn`): `00010003-9a74-4b30-9361-4a16ec09930f`
+    the reading from the Arduinos analog pin
+3. count: (`uint16_t`, `rw`): `00010004-9a74-4b30-9361-4a16ec09930f`
+    set the number of measurements to take with `MEASURE_COUNT`
+4. inteval: (`uint16_t`, `rw`): `00010005-9a74-4b30-9361-4a16ec09930f`
+    set the interval between measurements in ms
+
+