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It's hard to find a Handspring Visor these days, but... 

The Deluxe BrainStem PPRK is Visor compatible with the addition of the BrainStem-to-Visor Interface kit.  The modification described below tells how to make a Pontech SV203 PPRK compatible with the Visor. 

The Problem

There has been a great deal of confusion over making the Handspring Visor work with the PPRK.  "What's the deal, they run PalmOS and have a serial port, so it should just be a matter of getting a different connector, right?" Unfortunately, no. 

A Quick Intro to RS232 vs. TTL

Skip this section if you're already a RS232 master or you're not a geek.  The Visor, while it does have a "serial" port, does not have a RS232 serial port.  RS232 defines its logic levels as +12 volts and -12 volts (+/- 3V or so).  TTL defines its levels as +5V and 0V, or +3.3V and 0V in low-power applications.  This is the typical operating voltage of chips running in digital logic circuits, e.g.  the Visor.  Converting between TTL and RS232 requires a special chip and often some external components, so when handheld computers are looking to save space, this is the kind of thing that gets cut. 

As a result, any serial device attaching to the Visor needs to talk 3.3V logic-level serial instead of RS232.  You usually do this by inserting a chip -- usually a MAX232 or 233 -- between the RS232 device and the Visor.  The Visor "serial cradle" does this.  It's kind of a hassle, though, since you can't just solder up a connector and run with it.  I'll cover building a level-shifting cable in a future update.  In the meantime... 

Pontech Circuit Board Modifications

There's another way to solve the problem, however.  The Pontech controller also uses TTL levels on its board.  It uses a MAX489 chip to boost its signal levels up to RS232 on the serial port, so what if you just bypassed that chip and made the Pontech use TTL on its serial port? This winds up being an easy solution if you're familiar with soldering. 

That said, you'll need the following tools:

• Visor connector kit
• Soldering iron with fine tip
• Solder
• Desoldering Braid
• Small wire

First, take a look at the Pontech controller, the side with all the chips and jumper connections on it.  Now flip it over.  There's only one chip there, and it's the tiny surface-mount MAX489 serial level converter.  Fire up your soldering iron, hopefully one with a fine tip.  If you're a soldering pro, drink enough coffee to give you the shakes, otherwise this procedure might be too easy. 

Pontech circuit board modification region.

Use some desoldering braid to remove the solder from the chip's pins.  Now the chip should just fall off.  No, actually it still sticks there.  Take an XACTO knife and gently pry the pins away from the board while heating them with the soldering iron.  Or, if you're impatient, hack away with a small wire cutter. 

Wicking up solder.

Lifting the pins.

Now that you have the MAX489 chip off the board, look for the small dot on the board which indicates where pin 1 was on the chip.  (It'll be above the pin.) Ensure your orientation is correct, unlike what I did the first time around.  Now solder a small bit of wire between pin 2 and 11, and another between 5 and 10.  See the diagram and photo. 

MAX489 Pinout

Wiring it up.

Finished Pontech

That's it for the Pontech.  Now for the cable. 

Putting Together the Cable

This part is relatively easy.  You can use the parts in a BrainStem-to-Visor Interface kit.  The kit comes with a little PCB that goes in the housing, complete with pin numbers on it.  Solder the Visor connector to the PCB, then take a piece of cable scavenged from another serial cable (or something to that effect), and make the following connections:

• Visor pin 1 to DB9 pin 2
• Visor pin 4 to DB9 pin 5
• Visor pin 8 to DB9 pin 3

Once you figure out how to snap all the little pieces into the Visor connector housing, you're set.  Do the rest of your PPRK buildout and you'll have a Visor PPRK!

Related Links:

PPRK Frequently Asked Questions