Registered: Sep 1999
Location: Milwaukee, WI
Posts: 74

First let me say I don't need this, I have both cradles, but here is my idea.

Take the USB cradle that comes with the visor. Open it up. Take a serial cable. Solder the applicable wires from the serial cradle to the two simple serial pins on the visor connector (see the development manual for the pins).

You wouldn't be able to use the hot sync button to start a serial hot sync, but you could start it from the hot sync app.

Probably have to solder piggyback to the ground and possibly some other connectors as well.

Just an idea. Let me know if anyone does this.

Registered: Sep 1999
Location: Sacramento, CA, USA
Posts: 24

I tried this last night. Didn't work for me though. Didn't try the hotsync app though. Why wont the button work for serial?

I'll try it again when I get home tonight & post results.

Registered: Oct 1999
Location: Middleton,WI USA
Posts: 4

I've been tring to do this conversion also, but not much luck. I did try to pull the KBD signal low and was able to see transmissions in hyperterminal, but no luck with the hotsync program talking.

I looked up the specs on Handsprings site and they noted that the RXD and TXD signals are TTL level, not RS-232 level. Does this mean that an amplifier chip is required(or something along those lines)? Any EE's out there?

I think the reason I could get transmissions with the KBD tied low is that doing this provides up to 3mA max at 3.0 V. I thought maybe sinking KBD input told the device to use the simple serial interface instead of the USB.

Sure hope that I didn't do any harm to the CPU UART!!!

What's the factory serial cradle look like inside????

Registered: Sep 1999
Location: Sacramento, CA, USA
Posts: 24

Whoa, TTL level? I guess I should have paid closer attention to the specs.

Yes they are incompatible. You need a converter to get them to work together. Check out this page for some pretty good instructions:
http://www.e.kth.se/~e93_jbm/GH337/RS232.html

Pretty simple...Toughest part of it is finding +5v supply. I guess you could tap into the keyboard connector. A little too much time & trouble for me. If any of you hackers are up for it, post your results!

BTW Maxim will give you a few free samples of the IC if you need an incentive

On a positive note, I doubt if you did any damage to your serial port. RS-232 is a pretty robust (3-12 Volt) spec. Plus the UART's usually overvoltage/current protected on the PC.

Registered: Oct 1999
Location: Middleton,WI USA
Posts: 4

How does Handspring deal with this in their serial cradle?
Do they have an IC in the cradle? Is there a plug-in to the wall to power an IC, or do they get the power from the Visor? or?
It would be great if someone could open their serial cradle and post a reply.

Thanks

Registered: Oct 1999
Location: Las Vegas
Posts: 16

Just wondering.... wouldn't a USB to Serial adapter work?

Registered: Oct 1999
Location: Las Vegas
Posts: 16

Just wondering.... wouldn't a USB to Serial adapter work?

Registered: Nov 1999
Location: Kansas City
Posts: 19

KAB,

I was pretty sure that there was a way to p ull power off of the serial port, so I did a little digging. Check out:

http://people.ne.mediaone.net/fstewart/serial-1.html

under the section titled 'parasitic RS232 power'.

If you wanted to leave the USB plug plugged in, I believe one of the pins supplies +5V.

I haven't tried messing with the cradle yet, but since my serial cradle is on backorder and I can't hotsync, I'm tempted



[This message has been edited by bloonr (edited 11-16-1999).]

Registered: Nov 1999
Location: Kansas City
Posts: 19

It worked! Sort of...

With a MAX203 chip and about $10 of parts from Radio Shack, I cobbled together a TTL-RS232 converter that was powered off the serial port. (That fits in the cradle, no less.) I can see transmissions from the Visor in terminal when I try a modem sync.

Only problem is, the dang thing won't hotsync. Looking closer at the cradle connecter, I noticed there are a few empty places for some capacitors. When those are in place, it appears to short USB pins 1, 2 and 3 to ground. Perhaps that tells the visor to sync with serial instead of USB?

---11/29---
Just got my serial cradle, I'll poke around and see if I can figure out what makes the Visor sync one way or the other.

[This message has been edited by bloonr (edited 11-29-1999).]

Registered: Sep 1999
Location: Sacramento, CA, USA
Posts: 24

Bloonr,

Now that you've had time to poke around your serial cradle...how's it work? I'm dying to know so I can convert my USB cradle! If you could describe it (& maybe throw in some pix?) that would be great!

Russ

Registered: Nov 1999
Location: Kansas City
Posts: 19

Sorry, I took a break to play with my Visor after I got my serial cradle

The serial cradle is pretty much what I expected... There is a little chip that converts the TTL to RS232 levels, and a circuit that pulls power off of the RS232 signaling lines to power the chip.

The other important difference is that pin 2 on the cradle connector (KBD) is grounded. It isn't on the USB cradle. So, I took my "hacked" USB cradle, grounded the KBD pin, and it worked!

So, the "dual" cradle would need a switch to flip between USB and serial... no big deal.

Does someone have some web space that I can use to post the circuit diagrams & pictures?


P.S. The chip used in the Handspring serial cradle appears to have the same pinout as the Maxim MAX232

[This message has been edited by bloonr (edited 12-11-1999).]

Registered: Sep 1999
Location: Sacramento, CA, USA
Posts: 24

bloonr,

Cool! I have some webspace. Email me the pix & diagrams you have & I will put them up.

[email protected]

Russ

Registered: Sep 1999
Location: Sacramento, CA, USA
Posts: 24

I have posted bloonr's (Sean's) info on his cradle mod to my homepage.
http://russ.homepage.com

It's nothing fancy (I'm no HTML master), but it gets the info out there. Hope to hear about other success stories!

Registered: Dec 1999
Location:
Posts: 18

Has anyone tested bloonr's schematic with serial devices such as a modem?

Does the visor have support for serial devices or are drivers needed for the particular modem?

If serial devices can be connected to the Visor in this way, can USB devices be connected too? Will the Visor need driver support for this?

If I get the serial cradle, would I be able to connect it directly to an external modem without any modification (other than plain an adaptor so I can connect the two male connectors together) or will I need an adaptor that would change the pin configuration?

Any help would be appreciated. Sorry about all the questions, and thanks in advance.

------------------
------------------------
-Cyrus
[email protected]



[This message has been edited by Cyrus (edited 12-16-1999).]

Registered: Nov 1999
Location: South Riding, VA
Posts: 33

Wow, you guys are impressive. Now that you have ripped open your cradles, do you think there is a relatively simple way to modify a usb cradle to make a powered version that would not drain the visor batteries? I have looked at the specs and thought I saw which pin draws power. I guess you would disconnect this and reconnect to a transformer. Anyone?

Registered: Nov 1999
Location: Kansas City
Posts: 19

Maybe we should rename this topic "Cradle hacking madness"

Cyrus,
You CAN use the serial connection to talk to another serial device (modem, GPS) given the schematic. However, the KBD pin must not be tied to GND. Otherwise, the Visor will think you want to hotsync.

You could probably plug it right into a modem and have it work, might need a null modem adapter.

I don't think the Visor could drive USB devices because 1) it couldn't supply +5V to pin1, and 2) I think there are two flavors of USB device, "Parent" and "child" (or something like that), with the Visor being the latter.

geoffh -
There is a pin (VDOCK) on the cradle that is currently unused. It passes through to the springboard connector. It may be used in the future to power the visor or a rechargeable springboard. The USB connector does supply +5V on pin1, but I'm pretty sure the cradle doesn't use this for anything.

Registered: Dec 1999
Location:
Posts: 18

Bloonr: I think you're right. The documentation on the Handspring site said that the visor was a "slave" USB device.

I took a look at the schematic and I can't seem to understand why pin 7 on the MAX203 is connected to the DTR (pin 4), the RTS (pin 7) and the CTS (pin 8) on the 9-pin Serial. Are they supplying the 5+ volts? What does the 7805 do? What does the capacitor do? What do the diodes do?

Sorry again for asking so many questions and thanks in advance.


------------------
------------------------
-Cyrus
[email protected]



[This message has been edited by Cyrus (edited 12-16-1999).]

Registered: Dec 1999
Location:
Posts: 8

I was going about this almost exactly the
same way The tips here are great!
Thanks

Registered: Nov 1999
Location: Kansas City
Posts: 19

Cyrus,

DTR and RTS are pulled high (usually +5..12V) when the serial port is ready to to talk with the device (Hotsync app pulls these pins high, by the way.)

The 7805 is a voltage regulator, which regulates +7..18VDC to +5V, and the diodes/cap are part of the power supply circuit as well... not entirely sure why they're there, 'cause I'm not a EE!

Pin 7 and 8 are tied together to fake out the serial port handshaking. In most cases, this isn't needed. You may also need to tie DTR to DSR(serial pin6) to get the handshaking to work.

Has anyone seen this thread: ? http://discussion.visorcentral.com/...TML/001040.html

It's about building charging circuitry into the cradle. Neat!

Registered: Dec 1999
Location:
Posts: 52

You guys are reading backwards, if I would've seen this thread first, I would've done the Serial converter with the Charging circuits.