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Disclaimer: AT YOUR OWN RISK! I AM NOT RESPONSIBLE FOR ANY DAMAGE THIS DIY WORK MAY HAVE DONE.
BACKGROUND
I recently got a used t21 and really love it. I wanted to have wireless and bluetooth, so I picked up a 3com XJACK wireless pc card to go internal wireless(well, sorta). As for bluetooth, I know 3com makes one with XJACK antenna too, but I am afraid the two year old product may not support all the current protocols like A2DP or AVRCP and the reviews are not that great either. Another option would be a usb bluetooth dongle, however, pluging and unpluging is really annoying, plus you have the thing sticking out. So I decided to DIY internal bluetooth for my t21.
IDEA
The idea is to squeeze a usb bluetooth dongle thing into the thinkpad and hook it up to the usb port on the subcard. In order to make the only usb port availabe when needed, a switch is added to turn the bluetooth on/off, and when it's off, the usb port is free for use. Sorry no Bluetooth and external usb device at the same time.
Material
A usb bluetooth dongle I picked up a year ago for use with my desktop, it has CSR chip.
A small two way switch got from my old walkman tape cassette.
Couples of thin wires etc. A long one is needed as the Bluetooth antenna.
Procedures
Since we need to access the subcard, you basically take the thinkpad completely apart except the LCD screen. Please refer to the manual for instructions on how to dissemble a t21.
Bluetooth module preparation
Even though the bluetooth dongle I have is already very small, it's still too big to fit into the t21, after discarding the housing and cutting unnecessary circuit, I ended up with a tiny functional bluetooth module(20mmx15mmx1.5mm). Wrap it with electrical tape completely to ensure absolute insulation.
Bluetooth module placement
After completely taking apart my t21, I found two possible locations for the module, one is in between the battery and hard drive, underneath the mouse buttons; the other one is in between the modem jack and VGA port. I chose the latter one because the former one would require excessive wiring (from battery to usb port). By placing the module vertically, it fit in the spacing between modem and VGA very well and didn’t cause any tension.
Switch placement
I had a hard time placing the tiny switch and eventually settled down just in between the usb port and ps2 port 'cause whenever you want to use the usb port the switch will be easily accessible. As you know, a usb port is basically two power wires and two signal wires. I chose to connect/disconnect one of the signal wire to control the bluetooth module, because if you use one of the power wire, sure you could turn on/off the bluetooth module, but you would have problem hooking up an external usb device as I found out. You need to drill a small hole in the casing to access the switch. Since the switch I used was very small, I only needed to make a 3mmx1.5mm hole.
Wire soldering
Since you are soldering wires directly onto the subcard, any overheating or short-circuit may kill it, please do this carefully. In order to have decent reception, we need to solder an extra wire to the Bluetooth module as an antenna which will be placed along the sub card. I am no way an expert in soldering stuff, but after about 10min work, all the soldering work was done.
Time to assemble the thinkpad together and now you can enjoy internal Bluetooth without sacrificing the only usb port.