I’ve got a 1998 HP 200LX palmtop. Wikipedia describes it as:
a personal digital assistant introduced by in 1994. It was often called a palmtop computer, and it was notable that it was, with some minor exceptions, a MS-DOS-compatible computer in a palmtop format, complete with a monochrome graphic display, qwerty keyboard, serial port, and PCMCIA expansion slot.
What I wanted was a single “dongle” that will allow me to connect to the palmtop over USB as well as power/charge it. Unfortunately it require 12V DC to charge or run the plamtop so I’m going to need to use a DC/DC boost converter.
Some links for those that want know more about the HP 200LX
The USB to Serial system is designed around a FTDI FT232RL USB to serial converter and a SIPEX SP213ECA RS232 Transceiver. All of the RS232 signals are converted, this allow you to do full hardware flow control.
The HP 200LX uses a proprietary serial plug.It’s a 10 pin 2mm spaced double row plug.
|1||DSR||Data Set Ready|
|2||DCD||Data Carrier Detect|
|3||RTS||Request To Send|
|4||RxD||Received Data (by DTE)|
|5||CTS||Clear To Send|
|6||TxD||Transmitted Data (by DTE)|
|8||DTR||Data Terminal Ready|
|9||Shield||Cable shield, not used in my design|
The DC/DC boost converter is designed using a National Semi LM2735XMF. The boos converter should be able to supply 12v@200mA to the palmtop, this is enough to run it and charge the batteries. If you have other devices plugged in, modems or CF cards, you might go over the specified max current. There is a polyfuse to protect the USB port from over current in the event of a short circuit.
The PCBs are quite densely packed and measure 30mm x 30mm. I’ve kept the design rules at 8mil tracks with 8mil spacing.
I will heat shrink the board to protect it. I just left it off so you could see what it looks like.
The final board is quite small and easy to use and now that I can charge off USB I can charge the palmtop almost anywhere. The serial connection has been tested up to 115200 baud and it seems to work fine. Overall I call it a quite successful project.
On a side, the answer to “Why the hell would you want to build this for a 1998 DOS computer with no network connection and mono screen?”
the answer is:
’cause I can and it’s fun to completely over engineer a solution plus I was looking for an excuse to test ITead Studio and finally I needed a USB to Serial connection, then why not throw in a charger too.
You can download the Schematics, PCB layout from the git repository.
git clone git://stewartallen.org/hp200lx_psu.git
or you can just browse the repository.
HP 200LX USB / Power Supply dongle schematics and PCB layouts are licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.