Merge pull request #138 from kjmoore/cmjcu-docs

CMJCU documentation, many thanks @kjmoore

docs/Board - CMJCU.md

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+# Board - CMJCU
+
+The CMJCU is a tiny (80mm) board running a STM32F103, which contains a 3-Axis Compass (HMC5883L) 
+and an Accelerometer/Gyro (MPU6050).
+
+This board does not have an onboard USB-Serial converter, so an external adapter is needed.
+
+# Pins
+
+RX Connections
+ * PA0 - Channel 1
+ * PA1 - Channel 2
+ * PA2 - Channel 3
+ * PA3 - Channel 4
+ * VCC - +3.3v
+ * GND - Ground
+
+Serial Connections
+ * TX1 - Transmit
+ * RX1 - Receive
+ * GND - Ground
+ * 3V3 - 3.3v
+ * 5V  - +5v
+
+Power Connections
+ * Power +/- - 1 cell 3.7v
+
+Motor Connections
+In standard QUADX configuration, the motors are mapped:
+| Cleanflight | CMJCU  |
+| ----------- | ------ |
+| Motor 1     | Motor3 |
+| Motor 2     | Motor2 |
+| Motor 3     | Motor4 |
+| Motor 4     | Motor1 |
+
+It is therefore simplest to wire the motors:
+ * Motor 1 -> Clockwise
+ * Motor 2 -> Anti-Clockwise
+ * Motor 3 -> Clockwise
+ * Motor 4 -> Anti-Clockwise
+
+If you are using the Hubsan x4/Ladybird motors, clockwise are Blue(GND)/Red(VCC) wires, anticlockwise
+are Black(GND)/White(VCC)
+
+If you have wired as above, Motor1/Motor2 on the board will be forward.
+
+# Connecting a Serial-USB Adapter
+
+You will need a USB -> Serial UART adapter. Connect:
+| Adapter           | CMJCU                      |
+| ----------------- | -------------------------- |
+| Either 3.3v OR 5v | The correct 3.3v OR 5v pin |
+| RX                | TX                         |
+| TX                | RX                         |
+
+When first connected this should power up the board, and will be in bootloader mode. If this does not happen, check 
+the charge switch is set to POW.
+After the flashing process has been completed, this will allow access via the cleanflight configurator to change 
+settings or flash a new firmware.
+
+WARNING: If the motors are connected and the board boots into the bootloader, they will start 
+to spin after around 20 seconds, it is recommended not to connect the motors until the board
+is flashed.
+
+# Flashing
+
+To flash the board:
+ * Open Cleanflight Configurator
+ * Download the CMJCU firmware binary (https://github.com/cleanflight/cleanflight/tree/master/obj/cleanflight_CJMCU.hex)
+ * Select "Load Firmware [Local]" and choose the CMJCU binary
+ * Tick "No Reboot Sequence" and "Full Chip Erase"
+ * Connect the USB->Serial adapter to the board
+ * Select the USB-UART adapter from the top left box
+ * Click "Flash Firmware"
+ * You should see "Programming: SUCCESSFUL" in the log box
+ * Click "Connect" -> This should open the "Initial Setup" tab and you should see sensor data from the quad shown
+ * Unplug the quad and solder across the 2 "BOOT0" pins - This prevents the board from going into bootloader mode on next
+   boot, if anything goes wrong, simply unsolder these pins and the bootloader will start, allowing you to reflash. You cannot
+   overwrite the bootloader.
+
+# Helpful Hints
+
+ * If you are only using a 4 channel RX, in the auxilary configuration tab, you can add a "Horrizon" mode range around 1500 
+ for one of the the AUX channels which will result in it being always on
+ * Enabling the feature MOTOR_STOP helps with crashes so it doesn't try to keep spinning on its back
+ * When the power runs low, the quad will start jumping around a bit, if the flight behaviour seems strange, check your batteries charge
+