README: document project and connections

README.md

@@ -1,4 +1,5 @@
-This firmware template is designed for development boards based around [STM32 F1 series micro-controller](http://www.st.com/web/en/catalog/mmc/FM141/SC1169/SS1031).
+This is the firmware for the sound lever meter.
+It will read the measurements from a GM1351 sound level meter and send them over Bluetooth.
 
 project
 =======
@@ -6,48 +7,76 @@ project
 summary
 -------
 
-*describe project purpose*
+The GM1351 is a digital hand held sound level meter.
+It is available under multiple brands.
+There is no connector/interface to read the measurements.
+Instead I am using test point on the back of the PCB.
+This allows me to monitoring the interface to the LCD and read back the data displayed into measurements.
+
+The measurements are send transmitted over Bluetooth using a SPP module.
 
 technology
 ----------
 
-*described electronic details*
+The firmware runs on a [black pill](https://wiki.cuvoodoo.info/doku.php?id=stm32f1xx#black_pill) development board.
+It is based on a STM32F103C8T6 micro-controller.
+This will do all the processing and control the peripherals.
 
-board
-=====
+The Bluetooth module is a HC-05. 
+It should be configured to be a slave and offer a SPP profile.
+The measurement will be forwarded by the micro-controller over the UART part configured at 115200 bps 8N1.
+It will transmit the measurement in the format "123.4 dBa\n".
 
-The current implementation uses a [core board](https://wiki.cuvoodoo.info/doku.php?id=stm32f1xx#core_board).
-
-The underlying template also supports following board:
-
-- [Maple Mini](http://leaflabs.com/docs/hardware/maple-mini.html), based on a STM32F103CBT6
-- [System Board](https://wiki.cuvoodoo.info/doku.php?id=stm32f1xx#system_board), based on a STM32F103C8T6
-- [blue pill](https://wiki.cuvoodoo.info/doku.php?id=stm32f1xx#blue_pill), based on a STM32F103C8T6
-- [black pill](https://wiki.cuvoodoo.info/doku.php?id=stm32f1xx#black_pill), based on a STM32F103C8T6
-- [core board](https://wiki.cuvoodoo.info/doku.php?id=stm32f1xx#core_board), based on a STM32F103C8T6
-- [ST-LINK V2 mini](https://wiki.cuvoodoo.info/doku.php?id=jtag#mini_st-link_v2), a ST-LINK/V2 clone based on a STM32F101C8T6
-- [USB-Blaster](https://wiki.cuvoodoo.info/doku.php?id=jtag#armjishu_usb-blaster), an Altera USB-Blaster clone based on a STM32F101C8T6
-
-**Which board is used is defined in the Makefile**.
-This is required to map the user LED and button provided on the board
-
-The ST-LINK V2 mini clone has SWD test points on the board.
-Because read protection is enabled, you will first need to remove the protection to be able to flash the firmware.
-To remove the read protection (and erase flash), run `rake remove_protection` while a SWD adapter is connected.
-
-The Altera USB-Blaster clone has a pin header for SWD and UART1 on the board.
-SWD is disabled in the main firmware, and it has read protection.
-To be able to flash using SWD (or the serial port), the BOOT0 pin must be set to 1 to boot the system memory install of the flash memory.
-To set BOOT0 to 1, apply 3.3 V on R11, between the resistor and the reference designator, when powering the device.
-The red LED should stay off while the green LED is on.
-Now you can remove the read protection (and erase flash), run `rake remove_protection` while a SWD adapter is connected.
+This does not use a Bluetooth Low Energy (BLE) module because it does not fit the needs.
+There is no need to save energy since the device needs permanent power just for the display.
+There is a constant stream of data (not fitting BLE principles).
+The is a specified Classic Bluetooth profile for serial data: Serial Port Profile (SPP).
+BLE module use non-standard GATT characteristics for serial data transfer.
 
 connections
 ===========
 
-Connect the peripherals the following way (STM32F10X signal; STM32F10X pin; peripheral pin; peripheral signal; comment):
+Connect the peripherals as described below.
 
-- *list board to peripheral pin connections*
+MT3608 voltage regulator module:
+- IN-: ground
+- IN+: 5V
+- OUT-: ground
+- OUT+: IDC 2x3 pin 5 
+
+Set the MT3608 voltage output to 9V.
+This is meant to replace the GM1351 PP3 9V battery.
+It kind of also works with 5V, but the LCD is very dim.
+Since I don't know if the measurements remain accurate at 5V, I prefer to provide the voltage it was designed for.
+
+HC-05 Bluetooth SPP module:
+- STATE: no connect 
+- RX: USART3_TX/PB10
+- TX: no connect
+- GND: ground 
+- VCC: 5V
+- EN: no connect
+
+n-channel MOSFET 2N7000:
+- 1 source: ground
+- 2 gate: PB0, add pull down resistor
+- 3 drain: IDC 2x3 pin 2
+
+IDC 2x3 2.54 mm, micro-controller side:
+- 1: ground
+- 2: PB13, SPI2_SCK
+- 3: 2N7000 pin 3
+- 4: PB15, SPI2_MOSI
+- 5: MT3608 OUT+
+- 6: PA8
+
+IDC 2x3 2.54 mm, GM1351 side (solder wires on the PCB):
+- 1: B-
+- 2: LCD_WR
+- 3: D7/D8, on the text side, to control the ON/OFF button
+- 4: LCD_DATA
+- 5: B+
+- 6: LCD_CS
 
 All pins are configured using `define`s in the corresponding source code.
 
@@ -83,7 +112,7 @@ It is up to the application to advertise USB DFU support (i.e. as does the provi
 
 The `bootlaoder` image will be flashed using SWD (Serial Wire Debug).
 For that you need an SWD adapter.
-The `Makefile` uses a Black Magic Probe (per default), or a ST-Link V2 along OpenOCD software.
+The `Makefile` uses a ST-Link V2 along OpenOCD software.
 To flash the `booltoader` using SWD run `rake flash_booloader`.
 
 Once the `bootloader` is flashed it is possible to flash the `application` over USB using the DFU protocol by running `rake flash`.