I'm looking to setup a timing system for my Pedal Prix team (like car racing with drivers changing, only with "recumbent" (sort-of laying down) bicycles, and here is my current setup:

  • RFID Reader to ID the rider, connected to an XBee at 9600 Baud
  • GPS (to identify crossing the lap line) connected to another XBee at 115200 Baud (probably 115200).

I then obviously need 2 XBee receivers, and I'd like to connect both of these to one Raspberry Pi (both on GPIO pins if possible). (Arduinos and Pis draw too much current to be in the vehicle, and/or are superfluous to our needs.) Is this possible?

  • 2
    I will not answear your question, but I think that GPS is absolutely insufficient for race application. Even when using differential GPS, there is a precision in meters, so your lap line may float in +- 2 meters, for example. In race milliseconds and millimeters matters. Commented Aug 26, 2012 at 16:32
  • GPS is only accurate to 5-10 metres.
    – Jivings
    Commented Aug 27, 2012 at 8:23
  • I an aware of GPS accuracy issues. Honestly, at 30km/hr, that's 8.3m/s. So the difference is going to be at most 0.25 seconds (assuming 2 metres); that's a damn sight more accurate than hand-activated stopwatches. Commented Aug 27, 2012 at 10:06
  • Why use 2 XBees? If you get one RF channel running use that one to dump all the data you need.Set the GPS and RFID to TX on the one channel and the third(on the Pi) will listen to all data.(even at 9600) its fast enough! The Pi is more than capable of parsing and making sense of all the incoming data. Its using 2 Water connections, 1 for bath another for kitchen. There no need to do that at all
    – Piotr Kula
    Commented Aug 28, 2012 at 18:51
  • 1
    Fair enough. You might need a breakout board that can take more TTL inputs and multiplex them into one TTL that you can use on the Pi- I think re configuring the extra pins for another TTL input could be a bit of a mission.(possibly using TTL bit bang) I2C is an option but also the support is flakey for that now.
    – Piotr Kula
    Commented Aug 29, 2012 at 11:37

1 Answer 1


Per my comment on the reddit submission for this question:

I hope I am understanding the question, but as I understand it, this should be very easy.

All you need is:

  • an XBee breakout board (http://www.ladyada.net/make/xbee/),

  • an FTDI Serial-to-USB breakout board (https://www.sparkfun.com/products/9716),

  • and the XBee module itself (https://www.sparkfun.com/products/8742).

You can then communicate with the XBee via a virtual serial port opened by the FTDI driver, which is available on Mac/Linux/Windows. You can use Python and PySerial to open up a connection for each connected FTDI/XBee on your Raspberry Pi and have each channel send and receive data as desired.

Hope this helps!

  • I was trying to avoid using my USB ports, but if I want two serial ports, I can see this is the only option. I have replied to your Reddit post, my plan is to change the reader signal to i2c. Thank you! Commented Aug 30, 2012 at 0:41

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