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Tuesday, September 18, 2012

Wireless Serial on a Raspberry Pi

I don't have my Raspberry Pi yet.  RS has informed me of a delay - I guess the good news is I should be getting a Rev. 2 board.  In the mean time, a colleague of mine got his a while ago, but due to lack of time is letting me play with it.  I don't have time either, but I'm not letting me stop that!

So the first thing I did, not wanting to mess around with swapping monitors and keyboards etc..., was to hook up the Rπ to a bluetooth serial adapter I got off DX. ($8.60!, see also here)  It was trivial to hook up to the Rπ, but make sure to hook Vcc up to 3.3V! Otherwise, the TX line will probably output 5V TTL levels that could damage the Rπ input pin.  So, the hookup is, (adapter pin:Rπ pin) VCC: P1-01, GND: P1-06, TXD: P1-10, RXD: P1-08.

Software wise, there is not much to do either.  I left the adapter at 9600 baud; at some point I will send it the magic AT incantation to change that, but at the moment it was simple to just change numbers on the Rπ, all of which can be done on the SD card using another computer running Linux (in other words, the Rπ never needs to be hooked up to a monitor/keyboard).  In the boot partition, change the baudrates for ttyAMA0 to 9600, and in the actual real linux root partition, change the appropriate inittab line.  (details will follow - I don't have the board in front of me)

The biggest problem is the power.  As the Rπ (rev 1) does not have a halt or reset line, the bluetooth adapter will get power at the same time as the Rπ, so you cannot connect to it before the Rπ boots - on the Rev 2 board I think I could hold it in reset state until I've connected the bluetooth so I can monitor all bootup messages.  The other solution would be to give BT adapter its own 3.3V supply but that could also be dangerous for the serial input line of the Rπ.

1 comment:

  1. Also try Starman's Databridge wireless modules. They are easy to use and allow point to point or point to multipoint. They are a little pricier but well worth the quality and reliability.