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

Cyrus,

To answer your unanswered questions...

Either pin 4 (DTR) or pin 7 (RTS) is high (+5v to +12v) and the other is low (0v) at any given moment. They cannot both be high or low at the same time.

Each of the diodes act as a 1-way traffic cop, only allowing current to flow from the serial connector into the regulator, but not back into it's partner's pin.

Since DTR & RTS could potentially be switching polarity pretty rapidly, the 47uF cap is put across the regulator power input as an energy reserve. This keeps the voltage from dropping during a DTR-RTS swap.

Russ

Registered: Dec 1999
Location:
Posts: 2

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.

Registered: Jan 2000
Location:
Posts: 18

I have the stock visor serial connector and can't get it to listen to the garmin. Do i need to modify it to get powered continueosly while hooked up? I think this wi what I am reading looking at the posts above. I am getting desparate and may have to abandon the visor which I like(first pda) for a palm so I can map locate as this is the main reason I bought a pda. currently using a laptop but as you know they are a b to carry. I want to use gps pilot software any luck with others?

Registered: Jan 2000
Location:
Posts: 391

I've ordered the Visor connectors and the MAX203 chips. The connector fits very securely in the Visor, I wish the cradle had those little clips... it never feels quite secure.

I don't think my modem is generating all the right signals, I don't seem to have any power coming from the DTR line. Should I connect to DSR instead?

In any case I don't seem to have damaged my Visor (it still hotsyncs fine), but I'm not getting any communicating.

In the diagram Sean sent, what order are the pins read from? Is pin 1 at the right or the left when you are facing the front of the cradle?

[This message has been edited by argent (edited 03-20-2000).]

Registered: Jan 2000
Location:
Posts: 391

quote:

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Originally posted by Yours Truly:
I don't think my modem is generating all the right signals, I don't seem to have any power coming from the DTR line. Should I connect to DSR instead?

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Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

I have successfully built 2 serial cables using the design posted above. The circuit works great when attached to the PC. I think the problem you are having is that the modem is NOT generating the signals needed to power the circuit. I'm not really familar with the inner workings of RS232 but I believe that the signaling originates from the PC. RTS (Request to Send) and DTR (Data Terminal Ready) are on the host side. In that case, a battery pack to the input side of the regulator will probably do the trick. Or, maybe CTS (Clear to Send) and DSR (Data Set Ready) are supplied by the modem.

Also, keep in mind that while the Visor has serial capabilities, there are NO handshake lines; only RXD and TXD. This (again just a guess on my part) would preclude anything above 9600 bps UNLESS you are using software that permits software flow control (XON/XOFF).

I haven't tried my cables with a modem yet so I can't offer any help there. But the Developers Kit manual does talk about the 9600 bps limitation.

BTW... my 2 cables cost me a grand total of about $25.00 to build. The MAX 203's were free so that helped. As I said, I followed the details above with one exception: pin 2 on the Visor (in the drawing it's shown connected with a switch) is ALWAYS tied to ground (pin 4) in a serial application. I got this directly from HS Tech Support. That is how the Visor knows to look for data on the serial pins (this is also in the Dev Kit manual). I believe the original design was for use in a dual-cradle application... I made stand alone cables for portable use.

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MarkEagle - Ice is nice!

Registered: Jan 2000
Location:
Posts: 391

quote:

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Originally posted by MarkEagle:
I'm not really familar with the inner workings of RS232 but I believe that the signaling originates from the PC. RTS (Request to Send) and DTR (Data Terminal Ready) are on the host side.

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Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

Yes, I'm using it as a HotSync cable. I got the circuit into an ultra mini box about the size of an auto keyless remote. It is MUCH smaller than the cradle... even fits in my pocket.



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MarkEagle - Ice is nice!

Registered: Jan 2000
Location:
Posts: 391

quote:

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Originally posted by MarkEagle:
Yes, I'm using it as a HotSync cable. I got the circuit into an ultra mini box about the size of an auto keyless remote. It is MUCH smaller than the cradle... even fits in my pocket.

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Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

I used the Radio Shack ultracompact enclosure (#270-288). I did my own circuit board layout using one of their multipurpose grid boards (#276-149 cut to size) with lots of jumper wires. I even managed to get a sub-mini pushbutton switch in there. The diodes are actually mounted directly to the 9-pin connector, not on the main circuit board. This allowed me to keep things small enough to fit the box.

I'm toying with the idea of somehow combining the box and the HotSync connector together into one piece. I even think that if surface mount chips and components were used, the whole thing might just fit into the HotSync connector itself.

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MarkEagle - Ice is nice!

Registered: Jan 2000
Location:
Posts: 391

quote:

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Originally posted by MarkEagle:
I'm toying with the idea of somehow combining the box and the HotSync connector together into one piece. I even think that if surface mount chips and components were used, the whole thing might just fit into the HotSync connector itself.

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Registered: Apr 2000
Location: Texas
Posts: 20

I built on of the serial connectors from scratch but I am having a problem. If I use the hot sync button sometimes my Visor crashes with:

"Fatal Exception"

I then have to do a reset. It doesn't seem to do it when I activate the local sync in the HotSync manager. I am an Electical Engineer and I know nothing about the visor inner parts. Do I need to debounce the button? Has anyone had the same problem? Any ideas here would be great.

Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

EE_Fun,

An obvious question, but did you double-check the circuit for accuracy and to see whether or not there were any shorts?

I've built 3 serial cables and have never had the "Fatal Exception" error. Both the HotSync button and syncing from the HotSync app work just fine with all of them.

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MarkEagle - Ice is nice!

Registered: Apr 2000
Location: Texas
Posts: 20

MarkEagle,

What circuit did you use? I used the one linked earlier with the 7805 and the 47uf cap (should it be .47uf ?). What did you use for a cap?

The error "Fatal Exception" shows sometimes when invoking the hotsync using software, but it is rare. If I short the cap with another cap before pressing the button then it works every time.

Most cases in using a voltage regulator I think a cap is used on the in and out side of the 7805, I am thinking there is a problem in this area of the circuit design or some type of floating ground.

There is always the chance that I am missing or not seeing something, the thing is I have designed much larger circuits without any problems.

EE_Fun

Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

EE_Fun,

I'm guessing that you can sync sometimes but not always, correct?

I used the exact circuit described above... with a 47 uF capacitor (the same Radio Shack p/n that was given). And I've built 3 cables... all work just fine.

Out of curiosity, are you running EVPlugBase by any chance? There have been lots of reports of it being incompatible on the Visor (I had several errors and lockups when I tried it).


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MarkEagle - Ice is nice!

Registered: Apr 2000
Location: Texas
Posts: 20

MarkEagle,

This is how it works. If I first plug the cable into my Visor then use the button the error will show, but if I reset (which the error forces me a software reset) and don't unplug the cable then the button works. Lets say I disconnected the link after the reset then use the button again, it would give me the error again. Go figure?

Now if I use the Software in the Visor to start the hotsync then I am ok, but like everything else there is an exception. every once and a while it will give me an error. It is rare though. If I don't unplug the cable and use the button from now on it works fine.

No I don�t have that DB you mentioned, what I need to find out is what causes that error in the Visors software. I guess I will have to get into the PalmOS to find that out.

EE_Fun

This is an update, I fount out that my problem was software. I narrowed it down to about 3 programs. Which means the circuit works great!!!

[This message has been edited by EE_Fun (edited 05-13-2000).]

Registered: Dec 2003
Location:
Posts: 1

Serial Cable for connecting Visor Deluxe to an external modem

[QUOTE]Originally posted by MarkEagle
[B]I have successfully built 2 serial cables using the design posted above. The circuit works great when attached to the PC.

BTW... my 2 cables cost me a grand total of about $25.00 to build. The MAX 203's were free so that helped. As I said, I followed the details above with one exception: pin 2 on the Visor (in the drawing it's shown connected with a switch) is tied to ground (pin 4) in a serial application. I got this directly from HS Tech Support. That is how the Visor knows to look for data on the serial pins (this is also in the Dev Kit manual). I believe the original design was for use in a dual-cradle application... I made stand alone cables for portable use.

------------------

I am trying to make a serial cable for connecting my Visor Deluxe to an external modem (NOT a PC). I plan to use the Maxim 203 IC. I would appreciate if you could please send me the circuit you have used to build your cables. It does not seem to be available on this site any more.

Also, does the pin 2 on the Visor need to be permanently grounded for communicating with a modem, or is it required to be grounded only for a hotsync operation?

Any tips and advice would be greatly appreciated. Thanks in advance.

Netgains

Registered: Dec 1999
Location: Connecticut USA
Posts: 2682

Re: Serial Cable for connecting Visor Deluxe to an external modem

quote:

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Originally posted by netgains
I am trying to make a serial cable for connecting my Visor Deluxe to an external modem (NOT a PC). I plan to use the Maxim 203 IC. I would appreciate if you could please send me the circuit you have used to build your cables. It does not seem to be available on this site any more.

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Attachment: serial schematic.bmp
This has been downloaded 269 time(s).

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