Dr. Reddy's Guide to HP Palmtops

Bluetooth on a Palmtop

(it takes a little doing at present, but it can be done)

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The HP Palmtop Mailing List (on which I have been lurking for quite a while) has had several threads in the past on using Bluetooth on a Palmtop. Most of these threads haven't led to much, at least as far as I can tell -- which may indicate only that I haven't been lurking as well as I should have. I decided to try it myself, and actually got somewhere.

Part I: The Parts

The Bluetooth module I used is the Ezurio (formerly TDK's Bluetooth division) BISM-2 (Bluetooth Serial Module). It is small (22.8 x 33.8 x 7.6 mm), and draws a maximum of 65 mA with a 5V supply. (That's while waiting for a connection or when in "discoverable mode"; maximum draw with maximum-rate data transfer is 24.5 mA at 5V and 9600 baud, and 36 mA at 5V at 460,800 baud.) The underlying radio chip is from Cambridge Silicon Radio. You can buy the BISM individually, but the connector on the module is awfully tiny. I bought a Blu2i Development Kit from Tek Gear; it contains a BISM-2, a development board which has (among other things) a DB-9 male serial connector to access the BISM-2 with, a 120 VAC to 6VDC power supply for the board, a USB Bluetooth dongle in case your other computer needs a Bluetooth interface, a DB-9 male to DB-9 female cable, and two CD's with documentation and software (including a serial terminal program for Windows that's MUCH easier to use than HyperTerminal). The board also carries a codec and 2-way audio connector, and a parallel-port connector (DB-25 male) for reflashing the BISM firmware.

Rather than start out with custom connectors, I used the serial cable from the Connectivity Pack. Recall that the Connectivity Pack cable has a DB-9 female connector to plug into your desktop or laptop computer, and is therefore wired as a null modem so that your Palmtop appears to your computer as a modem. Since the BISM/development board is wired as a modem itself, I needed another null modem adapter (and a couple of gender changers, so that the extra null modem has DB-9 male connectors at both ends) to connect it to my Palmtop. The setup is shown below.

Palmtop-Bluetooth bench setup

The other equipment I used for my experiments was a laptop running Win XP, with the USB Bluetooth dongle plugged in. The dongle and the BISM-2 are configured to pair automatically when powered up. Dongle configuration is accomplished by the Win XP drivers; the BISM is configured with AT-style commands (see below).

Part II: Software Configuration

I already had WWW/LX installed on my Palmtop. I installed MochaPPP on my laptop and configured the two computers to talk to one another using Daniel Hertrich's suggested configuration; the only change I made was to set up WWW/LX to use the wired serial port. Initially I used 38400 baud as suggested by Daniel. (I later turned everything down to 9600 temporarily, but went back up to 38400 later with no problems -- I don't think this is the upper limit, but I'm still experimenting here.) Before proceeding further I ran the connection through the serial cable to verify that the WWW/LX-to-MochaPPP connection was functioning.

I then disconnected the serial cable from the laptop, connected it to the development board, shut down and restarted MochaPPP, and reconfigured it to talk through the Bluetooth dongle. (On my laptop I used COM6 for Bluetooth access. YSPMV.)

Configuring the BISM required two AT commands:

Once these commands are entered, the next Bluetooth device (the dongle on my laptop) that tries to connect to the BISM will be able to do so. I have tried to insert these commands into the "login script" in www.cfg, but so far I have not been able to make this work and have been forced to enter the commands manually through Datacomm -- which only has to be done once per session..

The Results So Far

With this setup I was able to view Web pages on the Palmtop using WWW/LX and HV.

200 LX screenshot

I have not yet been able to make Transfile work with this setup (I think it may be a problem with changing the laptop serial port in Transfile, but I'm not sure as yet).


(...from me -- but comments from you are welcome).

Yes, it's still in the kludge stage. Suggestions (especially for the hardware hackers in the audience):

Reduce the external bulk
I used the development kit and board for experimental simplicity. Tek Gear also offers an RS-232 mounting board which is a lot smaller than the development board.
Get rid of the external power supply.
The BISM-2 is supposed to draw at most 36 mA once a connection is established (65 mA while waiting for a connection or being discoverable). The actual draw is partly dependent on connection speed; 36 mA is the quoted draw during data transfer ar 460,800 baud, and at 115,000 baud it's 28 mA. We might safely draw that off DTR (I have to look more closely at the Palmtop hardware specs to see if that's possible).
Reduce the external bulk
The BISM-2 is 22.8 x 33.8 x 7.6mm -- about the size of a large postage stamp, although much thicker. Anyone think they could fit one inside a Palmtop?

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Copyright © 2006, 2007 Vinay N. Reddy, M.D. All rights reserved.
Written 08/27/06; last revised 10/30/07 counter