Like I wrote in this article, it is pretty easy to run the Carambola SoC stand alone. Today I finished the Carambola-MSP430 (for MSP430 stand-alone see this article) Piggyback I intend to use as a replacement for the current jumper wired brains of my Carambot.
The Carambola comes with 2mm pin connectors, I used a 2mm perf board to host the Carambola, and then piggybacked the MSP430 on a 2,54mm stripe board. The MSP430 communicates with the Carambola through UART1 with the help of uSherpa-Firmware and the uSherpa-Python-Client-API.
Since the Carambola on the Robot is powered from a 7.4V LiPo battery, two DC step-down converters from Pololu are used: one for 5V which goes to USB, and one for 3.3V which powers the logic of the Carambola as well as of the MSP430. The Carambola seams kind of picky regarding the 3.3V supply. I was not able reliably powering the Carambola by using standard LM7805/TS2940 regulators. The step-down converters are mounted in diagonal to the perf board, since the have a 2,54mm pin-out, and by placing them like so, I barely was able to solder them to some of the whole of the 2mm perf board.
An other thing a noticed about the Pololu Step-Down Voltage Regulator D24V6ALV was, that they do not come up reliably when SHDN pin is left open. The manual says, it could be left open, or connected to VIN to enable the board. Well leafing it open was no success, connecting it to VIN works well.
The following table shows, how pins of the Carambola are connected:
|From Carambola PIN||Connected to PIN|
|5V power supply for USB (21)||VOUT output of 5V D24V6ALV|
|3.3V power supply for Carambola (22)||VOUT output of 3.3V D24V6ALV|
|UART 1 TX uSherpa-communication (31)||RX of MSP430|
|UART 1 RX uSherpa-communication (32)||TX of MSP430|
|UART 2 TX for serial debug console (35)||RX of FTDI|
|UART 2 RX for serial debug console (36)||TX of FTDI|
|GND ground (37)||GND|
|UDP D+ for USB (38)||USB D+|
|UDP D- for USB (39)||USB D-|
|UPHY for USB (40)||3.3V to select USB master|