Control Board v2

= Status: Replaced =

= Description = Control Board v2 consists of a Base Board. MCU Board and Minicaps. The MCU Board is an exchangeable microcontroller board and the Base Board contains only traces from the MCU Board to the Minicaps (LED Minicap, LSM9DS0 Minicap, etc.).

Initial MCU Board will be STM32F4 based to allow as wide development as possible. Later on more focused MCU Boards with STM32F1/3, STM32W or STM32L can be made without the need of changing the Base Board or the Minicaps.

The MCU Board can be used independently of the Base Board as a standalone board. It is connected upside down to the Base Board to allow using male headers on top side of the board in both use cases.

Features of the MCU Board (at least STM32F4)

 * Power through USB or a 5V pin. Either one, not both.
 * Can be powered from the 3.3V pin which will leave the regulator disabled.
 * SWD for debugging and flashing. Must use 90 degree angle headers.
 * Boot-mode and reset through the extra pins in SWD header. Neither can be used together with a debugger.
 * Primary ways to flash a firmware is USB DFU (needs the boot-mode) or debugger.

Open questions for STM32F4 MCU Board

 * [CLOSED] Does the power line need a diode? No: MOSFET P-CH 20V 2.6A SOT23 is more efficient.
 * [CLOSED] Is the crystal series used in Radio Board suitable for this STM32F4 as well? Should be, ABM3C-25.000MHZ-D4Y-T
 * [CLOSED] What ESD/EMI IC for the USB? SN65220
 * [CLOSED] Is CONN USB MICRO B RECPT SMT R/A suitable Micro USB connector? Yes.
 * [CLOSED] Is TLV702xx suitable regulator? No, use TLV70133 TPS70933.
 * [CLOSED] How to enable no-boot-mode with pull-down resistors and boot-mode with a jumper in the SWD pins (between VDD and GND)? Boot-mode works only when debugger is not connected. Solution: MCU -> jumper to VDD -> 10k -> GND.
 * [CLOSED] Is it ok to enable reset only with a jumper wire on the SWD pins? Cannot be used when debugger is connected. Yes.

= Discarded topics =
 * Use a jumper to select powering either from USB or from PWR.
 * Placeholder for LSM333 (9DoF sensor from ST, not yet sampling)
 * That's why there are pins for a separate IMU board
 * Ability to power with LiPo when not using USB?
 * Regulator should support 3.7V - 14V?
 * Might be easier with 2.5V voltage instead of 3.3V but 3.3V might be more convenient for peripherals.
 * Reference regulator 3.3V voltage to STM32 analog unit.
 * No need to be that accurate (and that's too expensive) (and it makes it hard to bypass the actual 3.3V regulator and provide 3.3V directly to the board, if the reference regulator would need higher voltage).
 * FETs for GPIOS providing 3.3V from regulator

What if CBv2 is just an expansion board to STM32F3 Discovery?

 * Abandoned: Discovery too big, cannot proper attach "shields".
 * STM32F3 Discovery home page
 * 5V distribution point (1 in, multiple out)
 * Pair PWM power pins (4x2) (same as CBv1)
 * Jumper selection for connecting PWMs to board's 5V (same as CBv1)
 * expansion board should not cover user buttons nor the leds on the discovery

Functionality needed from the discovery

 * 3V (or 5V and a regulator?)
 * NRTS?
 * BOOT?
 * WKUP (PE6) to radio?
 * GND
 * 4x ADC; PC0-3
 * 8x PWM; PE2-5, PA0-3 (or for USART2?)
 * 4x GPIO (with FETs); PF0-1,9-10
 * 1x USART (GPS); PC4-5 no CTS/RTS
 * 1x USART (Radio); PB6-7 no CTS/RTS

Simplifications compared to V1 (2013-10-27: old plans)

 * Remove support for host side USB.
 * Power is provided from USB or 5V from PWR connector. Only one can be connected at any time.
 * Replace JTAG connector with plain SWD pins?
 * Put extra GPIO pins to IMU connector, possibly replacing 3.3V/GND pins

Changes/Fixes (2013-10-27: old plans)

 * V1 Errata
 * USB OTG FS (F3 doesn't even have HS).
 * Support only DFU over USB to and disregard the pull-down resistors on UARTs/CANs?
 * Check the RSSI line
 * STM32F3 for cheaper price?
 * Note that F1 and F3 are pin compatible and so is F2 and F4.
 * STM32F372RCT6/256k/32k 5.80€
 * STM32F303RCT6/256k/48k 6.72€
 * STM32F405RGT6/1M/192k 9.30€
 * Replace regulator with tps73733 and connect enable pin to 5V
 * Allows low-power use cases when providing 3.3V directly from some external source
 * Provides enough current for xbee and GPIOs
 * http://www.digikey.fi/product-detail/en/TPS73733DCQR/296-22681-1-ND/1698980
 * Two push buttons, one for reset and one for boot mode. Easier to get to boot mode.
 * Disconnect PWM 5V from other power rails. Keep two 5V pins for each PWM pair for chaining 5V from a PWM pair to the next one.
 * Allow disconnecting LEDs for low power use cases.
 * Put power led behind a jumper to allow easy disconnect? Or just remove the LED if not wanted?
 * GPIOs will be behind FETs so user led doesn't need a separate FET. Connect user led to GPIO1 via a jumper to allow easy disconnect?
 * What broke on CBv1 when the sonar was short circuited? Could it be prevented with something?