Palm Universal Cradle Modification

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This page demonstrates the modification of the original Palm USB cradle ('Universal Connector Cradle') to enable Palm RS232 / serial communication in addition to the USB hotsync capability.

Possible uses are: Serial hotsync on Win NT machines (NT does not support USB), connections to modems / cell phones for internet access, connections to GPS receivers or waypoint/route/track exchange with GPilotS (desktop application AND GPS unit) and similiar software.

With previous, non-USB Palm devices, Waypoint exchange from GPilotS to a host/desktop application was easy - the cradle supported the necessary
signals directly. The new USB equipped devices, M125, M130, M500, M505, M515 do no longer support this - the RS232 port that GPilotS uses for connection to the Host PC is not connected through the cradle.

Few people do know that those signals ARE available in the cradle, but are not fed out of the cradle to the desktop machine. It's easy to modify the cradle so that the RS232 signals can be used in addition to the USB HotSync.

You need a TORX6 screwdriver to open the cradle. If you don't want to buy it, take your cradle to your preferred tools supplier and 'test wether
this strange screwdriver fits'. You don't need a TORX6 to reattach the screws later - the tip of a knife will do.


The 4 screws sit below the 4 bottom pads of the cradle. Remove the little black bumpers that hide them and keep them safe..

If you open the cradle, the hotsync button will fall out of the top part. Keep it safe.

You will notice a small pcb with the palm connector on it as on the picture below. On the right side of the pcb, you will see some unused 'silver' solder pads with numbers next to them, like D1, D2, etc. The new 'E' series cradles (improved electrostatic immunity) will already have two wires connected to P1 and SH2, but it's no problem to solder another wire to them.

Those solder pads carry the RS232 signals of the Palm connector. For GPilotS waypoint exchange, you only need Tx and Rx, and a GND connection, so a three wire cable is sufficient. Since the USB port also carries the same GND signal, it would be okay to leave away GND and only connect Tx and Rx. But for this to work, the USB connector would have to be plugged in all the time, so I suggest a 3 wire connection. A piece of 4wire phone cable is sufficient. You don't need a shielded cable for this application.


The easiest way to do this is to buy an off-the-shelf RS232 cable (at least one side D9FEMALE). Cut the other end off at around 1.50m, strip,
and test which wire colors Pin2, Pin3 and Pin5 go to. Cut all others. If you don't have a multimeter for testing, the easiest way is to buy a D9Female connector with shell/housing + 1metre of 3-4 wire cable (e.g. phone cable), so you can make sure which wire goes to which pin number. D9 connectors have tiny numbers right beside the pins. Strip the cable end by 4-5cm so you don't have to get to close to the pcb with the stiff 5mm cable body.

Since the cable will leave the cradle at the back later, it's a good idea to solder the wires to the rear of the PCB. Just take the PCB off the cradle bottom part. Put a strain relief over the open end of the serial cable NOW!

Here's the wiring:
Cradle solder pad -> D9F connector

D1 (Palm Rx)-> Pin 3 (PC Tx)
D2 (Palm Tx)-> Pin 2 (PC Rx)
SH2 or P1 (GND) -> Pin5 (PC GND)

Be careful - P2 next to SH2 carries charging power - don't cause a short with P1 oder SH2 (both P1 and SH2 carry GND).

The pictures show a full wiring, including handshake signals. For GPS / GPilotS use, D1, D2 and P1 / SH2 are sufficient (red, orange, green wires).
The black cable on the right hand side is the original USB cable.

The cable with the D9F end can then easily be brought out of the back of the cradle (use a strain relief, if possible, and strip it over the cable BEFORE soldering it to the pads ;-)

You can also fix the cable inside the cradle with hot glue or similiar stuff to have some extra strain relief.
Just make a little V-cut into the base of the cradle where you want the cable to leave the cradle.

This is how the final assembly will look like - USB cable left side, serial cable right side.

You should now test the connection with your intended application - e.g. a waypoint exchange with GPilotS.
If it doesn't work, you may have mixed pin numbers 2/3 - just change them and give it another try - mixing Pins 2 and 3 doesn't harm anything.

Now for final reassembly, take the top part of the cradle top down, put the hotsync button into it's hole, then place the lower cradle part bottom up on top of it, so the hotsync button stays in place. Reattach screws and put the 4 bumpers back into place. They may need some fresh glue.

That's it!

This is a very simple modification, and it is also very smart - you can hotsync via USB, exchange waypoints with GPilotS, without switching or unplugging any cables - just start the applications. Both USB and RS232 can be connected to the PC the same time without any interference.

But make sure your HotSync manager is not configured for 'local serial' + 'local USB' hotsync (Dual mode). Uncheck the 'local serial' option by left clicking on the hotsync manager icon, otherwise hotsync manager blocks the COM port for waypoint exchange.

If you want this mod to support also handshake signals, e.g. for mochaPPP, serial hotsync or a modem/cellphone connection, you also have to connect:

Cradle solder pad -> D9F connector

D4 - (Palm CTS) -> DSUB9F Pin7 (PC RTS)
D5 - (Palm RTS) -> DSUB9F Pin8 (PC CTS)
D6 - (Palm DTR) -> DSUB9F Pin6 (PC DSR)

like shown on all the wiring pictures above.

For a modem/cellphone connection the wiring would have to go 'crossed' to a D9male connector, and thus would not fit the Host PCs COM port anymore. I suggest you stay with the D9Female with the wiring shown here, and use a crossed genderchanger for the modem/cellphone connection.

For full serial hotsync, activated by the hotsync button on the cradle, you have to remove the tiny ID resistor right above the hotsync button ('R202'). On USB cradles, this is in fact a zero-ohm resistor, a jumper.

If you change this to a 7.5k resistor, the hotsync button will activate a serial hotsync instead of using USB. If you want a switchable solution between USB and serial hotsync, use the 7.5k resistor, but place a switch between Pins ID1 (left PCB side) und D3 (right PCB side). If the switch is closed, the 7.5k resistor get's short, and a USB hotsync will be signaled. With the switch open, the short is removed, and the resistor comes into action for a serial hotsync. You don't have to replace the ID resistor with an SMD type - just desolder the zero-ohm jumper, and place an ordinary wired 7.5k resistor between Pins ID1 (left PCB side) und D3 (right PCB side) - the same pins your switch attach to. If you don't find 7.5k resistors, use two 15k resistors in parallel. They fit nicely on the back side of the pcb.

I will include pictures of the switchable solution later.


Carsten Kurz, 14.06.2002