doc: document project

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 crown counter.
 
 project
 =======
@@ -6,12 +6,14 @@ project
 summary
 -------
 
-*describe project purpose*
+The crow counter just counts how many (per day and in total) caps (e.g. crown cork) have entered the basket.
 
 technology
 ----------
 
-*described electronic details*
+An infra-red LED and photo-detector create a light barrier, broken when crossed by caps.
+An RTC keeps track of the days.
+2 TM1637 7-segment displays show how many caps passed in total and today.
 
 board
 =====
@@ -26,11 +28,24 @@ This is required to map the user LED and button provided on the board
 connections
 ===========
 
-Connect the peripherals the following way (STM32F4xx signal; STM32F4xx pin; peripheral pin; peripheral signal; comment):
+Connect the peripherals the following way:
 
-- *list board to peripheral pin connections*
+- IR LED: connected across 3.3V with potentiometer to adjust brightness
+- IR photo-detector: PB5
+- first TM1637 7-segment 4-digit display: CLK to PB6, DIO to PB7
+- second TM1637 7-segment 4-digit display: CLK to PB8, DIO to PB9
+- CR1220 to VBAT for the RTC
 
-All pins are configured using `define`s in the corresponding source code.
+note
+----
+
+at first I use a KY-032 infrared sensor detects when a cap passes through the basket.
+this modules the infra-red LED (set to 38 kHz), and has an IR demodulator (at 38 kHz).
+I though this would be less noise prone, particularly from external IR sources.
+turns out it is a lot more.
+I tested will the cap reflecting the IR, but this is sometimes to short, and the demodulator might not detect it.
+I tested with the cap breaking the barrier, but the IR demodulator doesn't allow continuous IR burst detection and has a hard time detecting when it is broken and restarted.
+in the end, a simple LED on and photo-detector to create a barrier is super simple and efficient.
 
 code
 ====