Registered: Dec 1999
I've spent days trying to make this work. I am going on a vacation tomorrow and I need my Visor to talk to a GPS.
Since I'm doing away with the cradle altogether, until I reread the post, I didn't realize that the switch on the Visor cradle pin 2 was to get the Visor into serial mode from USB mode. The reason I was confused is that when you put a momentary switch on pin 3 and ground it, the Visor goes into hot-synch mode. That would be useful to me (especially since I can now replace the cradle). But I guess I'll get nowhere until I short pin 2 to ground on my serial-only cable.
There are also a couple of other things I've learned.
First, a company called ATL Link at www.atlconnect.com or www.atllink.com, sells the connector that Handspring uses on their USB cable for $2.66 each plus shipping. It's called the "Hot Sync Connector Kit" and you can get small quantities if you call one of the names at the top of the Handspring page. I ordered 4 (but they double shipped me and let me keep the extra 4 free). First I tried to mold a connector of my own with sheet copper and clay and it was a disaster. Ordering the connector was much, much easier.
Another thing I learned is specific for a GPS. I have a Garmin GPS (eTrex) and the data cable only has 3 leads, input, output and ground. There are no handshaking signals, so parasiting power off serial pins 4 and 7 isn't possible. So I did away with the connections on pins 4, 7 and 8, the diodes and the capacitor. Instead, I'm attaching a 9 volt battery between pins 1 and 3 (ground) of the 7805 in series with an on/off switch. The switch is there so I don't use the battery power driving the max203 when I'm not using it.
Anyway, to recap, here's what I'm doing to make my GPS serial cable:
1) Visor cradle pin 2 is permanently connected to ground. (Ground is what pin 4 is attached to).
2) A momentary switch is attached between Visor cradle pin 3 and ground (for when I want to hot synch with the cable).
3) No connections to 9-pin serial pins 4, 7 or 8. Also no diodes or capacitor (though I may connect them in the future so I can have parasitic power for when I hot synch).
4) The positive lead (usually red) of a 9-volt battery connector is connected to a single-pole single throw switch which is connected to pin 1 of the 7805. The negative lead from the battery connector is connected to ground.
5) The serial connector is male and the pin ordering is reversed. That is, when you are looking at the front of the connector, pin 1 is on the left and pin 5 is on the right.
6) Finally, the position of pins 2 and 3 on the serial connector are reversed. Serial pin 2 on the picture (RS-232 out from the MAX203 (on the MAX203 it is attached to pin 5)) is now connected in the center of the top row of the 9-pin serial connector (pin 3). Serial pin 3 on the picture (RS-232 in from the MAX203 (MAX203 pin 4)) is now connected to the second pin from the left on the top row of the 9-pin serial connector. Ground is still connected to the farthest pin on the right of the top row on the serial connector.
One final note: As it stands, it won't be ready for a hot synch. I think that to do that, you would need a null-modem adapter and possible to connect pin 4 to pin 6 on the serial connector and pin 7 to pin 8 on the serial connector so the PC would be handshaking with itself.
Now I'm not an engineer and this is one of the first projects I'm working on, so if anyone sees a problem with what I've described I'd appreciate a post in this thread.
Thanks to all.