The objective of the Colorado project is developing a STEAM concentrator based on Raspberry PI accessing to a 802.15.4 network by using a Digi XBee module. To do that, it is necessary to connect the Raspberry with the Xbee module using a RS232 link, since both devices integrate at least one 232 serial port.
This document takes as base a Raspberry Pi board with a 40 pin connector (specifically RPi B+) and a Digi Xbee Pro S1 802.15.4 module. The description is suitable to be applied to any Digi Xbee module (S1, S2x, S3, standard or PRO) whenever the module specific power requirements were taken into account (see Powe Supply notes)
Serial connection
The modules connection can be simple, ie just by connecting the Tx-Rx lines, or can be more complex by connecting the hardware synchronization lines (RTS and CTS). In the first case a serial hardware control flow will NOT be feasible. Both wiring methods are covered in the next scheme, in which these connections can be seen:- Raspberry Tx output (pin 8) is connected to the Xbee DIN input (pin 3)
- Xbee DOUT output (pin 2) is connected to the Raspberry Rx input (pin 10)
- In order to provide hardware flow control support:
- Raspberry RTS output (pin 11) is connected to the Xbee CTS input (pin 12)
- XBee RTS output (pin 16) is connected to the Raspberry CTS input (pin 36)
If the hardware flow control option is being implemented, it will be necessary to allow Raspberry Pi to use its pins as RTS/CTS (disabled by default). To do that, follow the instructions defined in the VMW Productions site.
Power supply
Apart of the serial connection, it will be necessary to power the Xbee module from a supply generating, in case of using a Xbee S1 module, a voltage in the range 2,8V-3,4V and a max. current that will depend on the S1 module used, but that ranges from 50 to 340 mA (see power requirements on page 13 of the Xbee S1 User Manual) .The Raspberry Pi uses four of its pins as power outputs (check full Raspberry Pi pinout here):
- Pins 1 and 17 outputs 3,3V with a max current of 50mA. Though the voltage is in the Xbee voltage input range, the current is in the higher limit of the smallest module, so using this option is not recommended. Note, however, that in case of using a Xbee S2C (the standard version, NOT the pro version) the max current would be between 33 and 45 mA and therefore taking the power supply from these pins would be feasible.
- Pins 2 and 4 outputs 5V with a max current up to 1500mA (depending on the RPi power supply). This current is suitable to power the Xbee module, but requires a voltage regulation.
