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Hacking a Modem for your HPLX

John McDonald

May, 1998

 When I recently returned to a HP 200lx (after a brief flirtation with a US Robotics PalmPilot), one of the first things I was interested in finding was a decent modem. I had noticed that a lot of nice Internet software has been developed for the HPLX (i.e. WWW/LX, POST/LX, GoinAE Postal, etc.), and I decided that I would be using mine to stay connected while traveling. I sat down and made a list of what I wanted in a modem:

I started doing some research and found that the only portable modem options available for the HPLX are the PC Card ones. I had two concerns with these:

The first concern was my biggest one. If IAEm using a modem and run low on battery power, I want to be able to still use my palmtop, even if I canAEt connect. Also, most PC Card modems are designed for notebook computers and, while theyAEve improved on power consumption in the last few years, they still consume power too quickly for my taste.

The second concern could be solved with a combo modem/FLASH card, but having 80MB at my beck and call has spoiled me, and the largest combo cards only offer about 20MB. They also tend to be a bit pricey, and I already had invested in my FLASH card.

When I first had a 200lx a few years ago, I used a small Megahertz Pocket Data/Fax modem, which was 9600 baud. I still had it, but I wanted something a little faster and with longer battery life. I checked around, and the only company that currently offers an external pocket modem is Addonics. The problem is that itAEs powered by the serial port, which means the palmtopAEs batteries. No luck there.

Not to be deterred, I started reviewing my options. While sitting in my office one night, my eyes fell upon now-unused PalmPilot (not literally, of course. That would have been really messy.) Before becoming disillusioned with pen-based PDAs, I had bought a modem for the PalmPilot. The modem was powered by 2 AA batteries, and would run for around 5 to 6 hours on a single set of alkalines. It ran at 14,000 baud, and had a serial interface for the Pilot. It didnAEt have a fax capability, but I donAEt send a fax more than once a month anyway, so that wasnAEt a big deal. I can always e-mail a document to my secretary and have her fax it.

I pulled out the PalmPilot modem and took a closer look at it. HereAEs what I found.

The Nuts & Bolts

First, a disclaimer. If you decide to buy a PalmPilot modem and try this yourself, I am not responsible for any problems you may have. What IAEm describing here worked fine for me. If you try this and canAEt get it to work, you will have voided your PalmPilot ModemAEs warranty (big time!), and you will not be able to return it.

Before you begin, youAEll need some tools. HereAEs what I recommend:

This project also requires a delicate touch and a lot of patience. YouAEll be working with small, surface mount soldering and tiny wires, so if your idea of working with electronics is a large hammer and some duct tape, forget it.

For supplies, youAEll need the following:

Most of these can be found at your local electronics shop, except for the palmtop serial cable. YouAEll have to get that from Thaddeus or some other HPLX supplier, unless you have a spare one lying around.

The battery case you use depends on which type of batteries you want to use. The PalmPilot modem can handle either 2 AAAEs or 2 AAAAEs. 2AAAEs give you longer battery life, especially if you use the Energizer Lithium ones (10-12 hours versus 5-6 hours for 2 AAA alkaline). The AAAAEs allow you to use a smaller case. The battery case I used is an AA one, RadioShack part #270-382A. This case requires a 9-volt battery style connector, which you can also find at RadioShack.

The project case you use depends on how you want to layout the board and batteries. If you do them side-by-side, you can use a flatter, wider case. If you want to stack the batteries on top of the board (which I did), you need a taller, narrower one. The case I used is by PacTec, Model #K-FLX-2535, which is 2.5" X 3.5" X 1.275" (outside dimensions). Mouser Electronics (http://www.mouser.com) carries PacTec cases if you want to order one by mail, or you can check out your local electronics supply store. (If youAEre in the greater Boston area, check out Active Electronics on Washington St. in Woburn). You may have to buy several and try them out to figure out which one gives you the best fit (theyAEre pretty cheap - $3.00 - $4.00 each).

Now on to the real nitty-gritty.

The Real Nitty-Gritty

The first (and hopefully obvious) step is to open up the PalmPilot modem. The case is held together by 4 small Phillips screws. Remove those, turn the modem over and gently lift the front of the modem casing off. CAUTION: The ICAEs on the modem board are static sensitive, so use some static precautions (i.e. donAEt pet your cat before you start this).

When you lift off the case, youAEll notice that the battery is molded into the front of the case, and makes contact with the board via 2 small copper contacts (more on this later). What youAEll see looks something like the following:

The four screws you removed held the board in place, so itAEs loose now. However, youAEll notice if you try to lift the board up, there are two wires (one red, one black) that are attached to a small metal disc on the bottom case. ThatAEs the speaker. We need to remove that to get it all the way out. Gently set the circuit board aside (donAEt pull the wires) and get your X-acto knife out. CAREFULLY cut around the outside of the metal disc to remove the glue holding it down. YouAEll need to make several cuts around the perimeter of the disc to cut all the way through the glue. Be careful not to cut the two wires.

Once youAEre through the glue, you need to pry the speaker disc up. ItAEs got some more sticky glue underneath, holding it to the casing. Gently pry around the disc a little at a time until it comes up. DonAEt bend the disc. Once youAEve got it off, put a small piece of wax paper over the sticky side to protect the adhesive. YouAEll be using it again.

Now youAEve got the circuit board free (at this point, your warranty is good for starting a fire with, and nothing else). Now pop off the black plastic casing thatAEs over the 10 edge connectors at the top of the board (labeled 1-10 in the diagram above). Underneath is another black plastic casing ^u pop it off, too. Now, snip off the 10 copper spring connectors at their base. You should end up with 10 flat copper strips.

Next you need to trim back the 10 edge connectors and the PC board underneath them. How much depends on the case youAEll be putting this thing into. The following figure shows where to snip: (for the case I used, I left about 1/8" of the connectors)

 I used a PC board snipper (available at RadioShack or other electronics supply stores). You could also use a fine saw to cut it.

OK, now for the last desacration. You need to decide what you want to do with the phone line connector. You can either use a female one, which means youAEll need a phone cable to connect, or you can directly wire in a male one with a short cable that runs out of the box and connect to the phone. I chose to use a female one, since I have one of those portable roll-up phone cables.

I decided to use the phone line connector thatAEs on the board. To remove it, snip the two metal tabs on the sides and the four metal connectors in the back. Once youAEve done that you can lift it right off the board. Even if you decide to use a male connector and a cable, you should go ahead and take the female connector off the board, as it takes up a lot of space. You can solder your wires to your choice of connector later on.

Enough Destruction

Now youAEve done all of the disassembly you should need to do. ItAEs time to start putting things together. First, get your cable ready. If youAEve got a whole cable (i.e. palmtop connector on one end, DB9 serial on the other), youAEre going to need to cut it. How much cable you leave is up to you. It should be long enough to comfortably reach the palmtop from the modem box, plus about 2". I cut mine about 10" long.

Strip off about 2" of the outer black cover and the metal shield. That should leave you with 10 different colored wires. Strip about ¼" of insulator off the end of each wire, twist the strands together, and tin the ends of the wires (coat them with solder). I could make this easy and tell you which colors you need to connect to which connector on the modem, but experience has shown me that not all of the cables use the same color wires. This is where the VOM comes in. You need to figure out which color wire goes with which pin on the palmtop. The easiest way is to stick a wire into each hole in the connector and see which wire it correlates to. Be careful to associate the right palmtop pin with the right wire. Remember, the connector is backwards from the pin layout. To illustrate, the following diagram shows which hole in the connector on the cable goes to which pin on the palmtop. It is the view looking at the connector at the end of the cable ^u the numbers represent which pin on the palmtop that hole connects to:

Use the following table to write down which color wire goes to which pin:

Pin #

    Color
1
2
3
4
5
6
7
8
9
10

Now weAEre ready for the case. Play around with laying out the components (i.e. circuit board, battery holder, etc.) in the case to make sure you get a good fit without cramming stuff together. On mine, the circuit board fits perfectly inside the case (after trimming the edge connectors), with the batter holder connected to the inside of the front cover over the side the phone jack used to be on. Once you are comfortable with the layout of everything, you need to drill a hole in the case for the palmtop serial cable. Use a drill bit that is the same size or slightly smaller than the cable to get a snug fit. You will also need to make a hole for the phone jack.

If you decided to go with a male connector and wire, make a hole the same size or slightly smaller than the cable youAEre using. Make the hole on the opposite side of the case from the palmtop serial cable.

If youAEre going to use the female jack that came with the modem, you need to cut a slot to fit it into. Cut the slot on the opposite side of the case from the palmtop serial cable. The slot should be wide enough to fit the jack snugly. Also, you may have to make it a little deeper than the jack is tall, to allow room for the lip of the cover to fit. Play around with it until you get it right.

HereAEs a diagram of how my case looks:

 

The four circles in the corners are the posts that the screws go into to connect the top of the case. Note that you havenAEt connected anything yet ^u youAEre just positioning things.

Once you happy with the way things are positioned, itAEs time to do some soldering. First you need to connect up the phone jack (or cable). Remember the four connectors that you cut on the back of the phone jack? Well, you need to solder the two middle wires from the phone jack to the two middle connectors that are left on the board. (Note: you donAEt have to re-use the connector that came with the modem. You can buy phone jack connectors at any electronics shore.) Looking at the connector, you should see four wires at the top on the inside. These are what the small metal strips on a phone connector make contact with when you plug the phone line in. At the bottom of the phone jack are four metal posts that correspond to these four wires. The following figure shows what I mean:

You need to solder a short length of wire to pins 2 and 3. The other ends of these wires go to pads 2 and 3 on the board (the middle two of the four you cut from the back of the jack when you removed it). The following diagram shows where they are:

 

Use a length of wire that is long enough to reach the back of the jack without pulling. Also, use #22AWG wire for these (phone lines carry a pretty high voltage).

Now itAEs the batteries turn. You need to solder the wire from the positive side of the battery connector you chose to the positive pad on the circuit board (labeled aePosAE in the diagram above) and the negative wire to the negative pad (labeled aeNeg" in the diagram above). These pads are little flat copper strips. Be careful when soldering the wire onto them ^u as they get hot, the solder holding them to the circuit board will melt, and if you are exerting any sideways pressure, theyAEll slide out of place. Gently press down on them with a soldering iron to heat them, melt a small bit of solder on each, then press the wire onto the solder dot and hold it until the wire sinks into the solder.

Last but not least, you need to connect the palmtopAEs serial cable to the board. Make sure you run the cable through the hole in the case BEFORE you solder the connections (itAEs very frustrating to have to undo them and re-do them)

Use the table you filled out above and make the following connections:

Palmtop Pin

Modem connector

2

3

3

5

3

1

5

10

7

4

8

6

Notice that not all 10 of the palmtopAEs pins are connected. You can cut off any wires that arenAEt used.

Some Assembly Required

Now youAEre ready to start assembly. First, take the wax paper off of the speaker disc and stick it to the bottom or side of the case (inside, of course). If you want better sound, drill a small hold through the case under the speaker before you attach it.

With the circuit board in place, locate the connector for the AC adapter. Remove the circuit board and drill a hole in the side of the case to allow the adapter jack through (assuming you want to be able to use the AC adapter).

Next, put a small dab of holt melt glue onto some 1/8" standoffs and attach them to the bottom of the circuit board at the corners. (Note: if you use the PacTec box I used, the standoffs are already built in. However, youAEll need to trim them down to 1/8" before you put the board in). Put a small dab of hot melt glue on the other side of the standoffs and place the circuit board inside the case.

Now put some super glue on the side of the slot you cut for the telephone jack and slide it into place.

Lastly, glue the battery case to the inside of the lid. Position it so that it will fit over the circuit board when the lid is closed. Put some batteries in and youAEre done!

Post Modem

Anyone thatAEs familiar with electronics knows that what IAEve described here isnAEt as easy as it sounds. You need to test every connection as you go along, and double and triple-check everything. Every connection is a possible point of failure.

If youAEre comfortable with electronics and have a desire to hack around, this project is probably for you. If your idea of a serial connection is a bowl of CapAEn Crunch, you probably shouldnAEt be doing this.

If you do decide to go ahead with the project and run into some problems, hereAEs a list of the most likely causes:

IAEve been using my hacked modem for a couple of weeks now, and it works great, so I know it can be done. However, I canAEt promise that youAEll have success if you try. I also canAEt promise that IAEll be able to help if you try it and canAEt get it working.

John McDonald

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