doc: add brief project description

README.md

@@ -1,4 +1,4 @@
-This firmware template is designed for development boards based around [STM32 F4 series micro-controller](https://www.st.com/en/microcontrollers-microprocessors/stm32f4-series.html).
+firmware for the Bahn Uhr controller.
 
 project
 =======
@@ -6,17 +6,31 @@ project
 summary
 -------
 
-*describe project purpose*
+This is the controller for a salvaged and modded Bahnsteig Uhr:
+
+- the track is made of white translucent ceramic, and RGBW LED strips illuminate it
+- a motor uses the dial drive to turn the dials (in theory with settable time)
+- LED panels allow to show text on both sides
+- controllable over the network using Art-Net
 
 technology
 ----------
 
-*described electronic details*
+controller comprises:
+
+- a [STM32 F4 series micro-controller](https://www.st.com/en/microcontrollers-microprocessors/stm32f4-series.html)-based black pill
+- a DRV8825 stepper motor allows turning the dials (hour is linked to minute)
+- reed switch, to home dial
+- P1 RGB LED panel (128x64), to display text on front side
+- WS2812b panel (2x 32x8), to display text
+- nMOS transistors to control 12V LED strips, to illuminate the track
+- ESP8266-based ESP-01 to connect to network
+- power connectors (0,5,12V-4pin and 12V-barrel input, 5V outputs for LED panels, 12V for motor and LED strips)
 
 Art-Net
 -------
 
-The Bahn Clock controller gets data over the network using Art-Net.
+The Bahn Uhr controller gets data over the network using Art-Net.
 The mapping is as follows (universe without offset, channel, target).
 
 clock illumination color (RGBW LED strip):
@@ -92,9 +106,6 @@ The underlying template also supports following board:
 
 - [WeAct MiniF4](https://github.com/WeActTC/MiniF4-STM32F4x1), based on a STM32F401CCU6
 
-**Which board is used is defined in the Makefile**.
-This is required to map the user LED and button provided on the board
-
 connections
 ===========