Minstrel hacking

I've hacked my Minstrel from Novatel Wireless to be used with a standard RS-232 serial port. The Minstrel is a CDPD (Cellular Packet Data) modem that very cleanly integrates with the Palm Pilot. It is shaped like the Pilot's cradle and includes the non-standard 10 pin male connector that mates to the Pilot's Hot-Sync connector.

It is really a standard RS-232 serial port, but it is difficult to find any connectors that will mate to this non-standard form. The only one that I could find was the The Bridge (scroll down to find it) from Pilot Gear. The price has dropped considerably since I purchased mine -- too bad for me.

The pinouts I snarfed from Ron Nicholson's Palm Pilot Information Page. I am reproducing his table here, with the modifications necessary to build the Minstrel cable:

Pinout (left to right, facing the front of the cradle) seems to be:

cradle  cable           Notes
------  -----           -----
pin 1   DE9.4, DB25.20  PC DTR -> Minstrel DSR
pin 2   N/C             Short to Pin 1
pin 3   DE9.2, DB25.3   Minstrel TxD <- PC RxD
pin 4   DE9.7, DB25.4   Minstrel CTS -> PC RTS 
pin 5   DE9.3, DB25.2   Minstrel Rxd -> PC TxD
pin 6   DE9.8, DB25.5   Minstrel RTS <- PC CTS 
pin 7   N/C             GPIO input pin for detecting hotsync, contacts
                        with pin 2 when the hotsync button is pressed.
pin 8   N/C             GPIO (input only, not connected in cable)
pin 9   N/C             N/C  (spare?)
pin 10  DE9.5, DB25.7   Signal Ground

N/C     DE9.4, DB25.20  (PC DSR not connected to PalmPilot)
N/C     DE9.1, DB25.8   (PC DCD unconnected to PalmPilot)

(Cradle uses single sided gold PCB edge connector with 2mm contact spacing.)

Ok, so you have the cable built and connected to the Minstrel. Now you need to configure the software. I have heard reports that it is possible to use Op Center software for the Sage modem (also from Novatel Wireless) to use the Minstrel with Windows, but I am running Microsoft free and so can't comment on this. Here are my two Linux PPP scripts to initialize the Minstrel:

#!/bin/sh
# /etc/ppp/minstrel

exec pppd			\
	/dev/ttyS0 19200	\
	debug			\
	crtscts			\
	defaultroute		\
	modem			\
	-vj			\
	connect /etc/ppp/minstrel-on

and

#!/bin/sh
# /etc/ppp/minstrel-on

exec chat -v 			\
	''	'\r\r'		\
	'0'	'ATE1V1\r'	\
	'OK'	'ATS57?\r'	\
	'OK'	'ATS202?\r'	\
	'OK'	'AT\APPP\r'	\
	'CONNECT'

So, what sort of performance can you expect? With my Minstrel, I usually see around 800ms round trip times for ping's ICMP packets. Very low packet loss, however, which means that even with that high of a latency the interactive performance is acceptable. On the good side, the CPDP machines are assigned static IP addresses, so you can set up an alias in your local DNS for your mobile unit. My recent tests with ftp showed about 600 bytes/sec for a single channel and 1000 bytes/sec with two channels.

Try to access my web server to see if my machine is online. Not likely, but hey, it is sort of fun anyway!

So it all works, right? Please send me mail if you get things working from this description. There are many weird problems that I have encountered with the Minstrel -- for example, my cable doesn't work on everyone's laptop and other machines have problems negotiating PPP addresses. For newer version of pppd, you must turn off VJ compression and sometimes assign it the IP address on the pppd command line. It is odd.

You may be interested in my comparison of the Palm VII, Ricochet and the Minstrel. This topic has been widely discussed on DejaNews.

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