Handspring Visor Page

Handspring Visor Links
http://www.handspring.com Handspring
http://www.visorcentral.com VisorCentral
http://www.mikew.org/html/visordeluxe.html MikeW.org's Visor Deluxe Dissection
http://www.interlog.com/~tcharron/Palm8M/upgradeservice.html Palm Connected Organizer memory upgrades

Development Tools
http://www.palmos.com/dev Palm OS Platform Developers
http://mot-sps.com/products/index.html MC68EZ328: DragonBall EZ Integrated Processor
http://www.atlconnect.com ATL Technology (plastics and connectors)

Other PDA Links
http://www.pocketaprs.com/visor.html pocketAPRS (information on RS-232 with a Visor)
http://home.satx.rr.com/pbasten/visor/visor.html pbasten's Visor serial cable
http://www.markspace.com/cables.html Mark/Space (Datacord HS serial Visor HotSync cable family)
http://www.atlconnect.com/thirdparty/handspring/pricing/connectors ATL (serial HotSync cable)
http://www.cables4pdas.com Cables4PDAs (Visor/Motorola data cable)
http://mobile.yahoo.com Yahoo! Mobile
http://www.pdabuzz.com PDABuzz
http://www.pricewatch.com Great prices on Computer goods

GPS Links
http://joe.mehaffey.com Joe Mehaffey and Jack Yeazel's GPS Information Website.
http://joe.mehaffey.com/default.htm#FAQs GPS Hardware Information.
http://celia.mehaffey.com/dale/phardware.htm Detailed GPS-specific Palm Hardware Information.
http://pfranc.com/projects/g45contr/g45_idx.htm Larry's Garmin Connector, now with new ePlugs for the Garmin eTrex and eMap.

Visor HotSync Serial Cable Compatibility Chart

MicroPower HotSync Serial Cable

Theory of Operation

After taking some measurements of the HotSync port's electrical parameters, I realized I needed some signal inverters between the Visor and the GPS. I tried diode-based and BJT-based designs to do the signal inversion. But they drew too much power from the HS1 or KBD pins, and would either go into HotSync mode or simply not work. I figured my only solution is to use ultra-low-power inverter gates, based on the newest CMOS technology. Thankfully, Texas Instruments has some nifty 1-Gate chips that draw very little current, and come in very small surface-mount packages. Fairchild Semiconductor makes a similar line of TinyLogic chips as well. I decided to use the TI SN74AHC1G14 Schmitt-Trigger Inverter Gate, although any inverting gate ('04 INV, '00 NAND, '02 NOR, etc.) would suffice by tying the 2 inputs together. You should be able to substitute gates from other low-voltage CMOS logic families such as VHC, LVC, etc. Here is the schematic:

D1 will help to clamp input voltages to roughly between -0.7V to +7V, which are just beyond the limits of the inverter gates. D1 can be a 1N4735A, 1N5250B, or BZX84C6V2 6.2V zener diode. If you're really worried about negative voltages, you can add an additional 10-ohm resistor R2 on the RXD line (in series between DB-9 and cathode of D1), as well as a 1N5817 or BAT54 Schottky diode D2 in parallel with D1. This should limit voltages to -0.5V, within the maximum ratings of the inverter gate. If you're worried about transients and line droop of HS1 (happens when the serial device draws more than about 1mA on its RXD input pin), you can also add a small 1uF or 10uF tantalum capacitor in parallel with C1. I like to go with the bare minimum for basement projects.

I purchased some HotSync connectors from ATL Technology, and was relieved to find room in the connector to squeeze the gates in. Don't forget to order the strain reliefs too - they really dress up the cable! By cutting off the unused Mac ADB connector from my Serial Cradle, I now had all the parts needed to build the cable, minus the printed circuit board (PCB). This is what my first-pass PCB layouts look like. The top layout accomodates the DCK/SOP package (0.65mm pin spacing), while the bottom one uses the DBV/TSSOP package (0.95mm pin spacing). All resistors are zero-ohm surface-mount (0805 or 1206) jumpers to avoid the need for a 2-sided PCB. Note: Reference designators shown do not match the schematic, and are there to help with orientation during "kitchen-sink" board manufacturing.

My first prototype (middle picture, left) uses the DCK package, which was somewhat of a challenge to do. I have since built up more versions using the DBV package (middle picture, right). I have also found a way to piggyback the protection diodes D1 and D2 onto the same layout, until I get around to making the next batch. They're the SOT-23 (6.2V Zener) and MELF (Schottky) devices at the bottom of the PCB.

I verified that the GPS 315 outputs 0V to 5.9V for quasi-RS-232 signalling, and will happily accept 0V to 3.3V for input voltages on its RXD pin. This is in agreement with general concensus that modern serial devices use 1.3V to 1.8V as the threshold voltage, rather than the official -3V to +3V deadband spec for RS-232. If you don't believe this claim, take a look at virtually any RS-232 transceiver's (MAX232, etc.) Vth spec.

Quick-n-Dirty In-Car GPS Setup
Using Energizer Accu 700mAh NiMH AAA's for the Visor, battery life is over 5 hours of continuous operation while connected to the GPS. Using the Visor alone, the NiMH's have lasted anywhere from 11 hours to 15 hours. The GPS is run off the 12V car adaptor, although it can also run on a pair of 1300mAh NiMH AA's. On the NiMH's, I get about 2-3 hours of runtime before the GPS shuts itself off. On alkalines, the GPS runs for over 8 hours.

I've made a convenient dash mount by using a sponge (an Eddie Bauer de-fog sponge) to hold the Visor up in my Subaru's pull-out cupholder. It 's out of the way of the shifter, yet still within easy reach for Graffiti input to Solus Pro 1.5. It's much more convenient (and safer!) than holding it in my hands.

The GPS mount at the left corner of the windshield works very well, and is adapted from a generic cell phone suction mount I got at K-Mart. At $10, it sure beats the $40 Magellan windshield mount. I used a small elastic loop at the top and some weatherstripping foam on the sides. As for the HUD, you can check out the installation how-to elsewhere on this web site.

Using BatteryInfo, I've had the NiMH's from 2.54V all the way down to 1.95V with no problems. I've even run with the Visor backlight on at night, and it works beautifully! Battery drain, of course, will go up. If you're using a similar Visor/GPS setup, just remember to set the PalmOS sleep timer to the maximum of 3 minutes, and occasionally switch back and forth between Map/Navigation/Direction modes, or else the Visor will turn itself off frequently. Even if that happens, reloading Solus Pro from the Application screen will update the map position in only a few seconds. For stretches of road where I don't need the GPS and the Visor is off, I usually disconnect the HotSync cable just to remove even that tiny bit of current drain (a mere 2-10uA) on the AAA's.

Tip: Thanks to Rudy of Handspring Technical Support Europe for this tip to disable the auto-off feature:
1. Make the Graffiti shortcut symbol (a cursive lowercase L) in the launcher.
2. Type a dot (two taps), followed by the number 3.
3. You should hear a long beep (if System Sound is enabled) to confirm that the auto shutoff has been disabled.
4. A soft reset will be required to disable this mode.
This link has more information on Graffiti Shortcut Characters.

External Modem Setup

Thanks to MPM on the VisorCentral forum, I got the Microcom 415 external modem to work with my Earthlink account. Now I can surf the Net using Avantgo and EudoraWeb at V.90 speeds. The external modem setup is not as elegant as the Springboard modems, but I can't argue with the $40 price (found it at pricewatch.com).

Group Buy Updates

I started a "group buy" in December 2000 on a VisorCentral.com discussion forum to gauge demand for building more cables. Please see Group Buy - wac's Serial HotSync Cables for details. This picture shows what the cable will look like, except that it's missing the HotSync strain relief, and the HotSync connector top and bottom halves will be assembled. I will add the strain relief once I get the next order of connectors in from ATL.

The "group buy" on the VisorCentral.com discussion forum has since been closed. I will not be building any more cables for the forseeable future. If you need a serial cable, please contact ATL and/or Mark/Space.

I'm still going through the "group buy" cables. Progress has been very slow due to my time constraints and troubles with obtaining parts. Anyone looking for a Visor serial cable should contact Mark/Space for a Datacord HS. They are increasing production to meet unexpectedly high demand for the Datacord HS. If you absolutely must have a Visor serial cable right away, you may purchase a GPS Adapter Cable from Delorme. The Delorme cable is very similar to the Datacord HS, but has been specially modified to work with the Delorme Earthmate GPS receiver. However, it should still work with handheld GPS receivers from Garmin, Magellan, and others.

HotSync Serial Cable FAQ

What makes it a MicroPower cable? How is the MicroPower Serial Cable powered?
The electronics inside this cable uses very little power. Therefore, this design is able to steal power from the HS1 pin without affecting Visor operation at all.

The MicroPower cable does not meet the official RS-232/EIA-232 serial communications standards. Notably, the standards specify negative voltages. Are you sure it will work with serial devices?
No. But yes, it will work. It works by taking advantage of industry-standard design practices for implementing RS-232 communications, which do not require negative voltages for signalling. The Magellan handheld GPS receiver I measured do not use negative voltages. I read that Garmin handhelds do not output negative voltages either, but are tolerant of them on the inputs. This information can be found in the Physical Protocols chapter in the GARMIN GPS Interface Specification document.

Can I use NiMH batteries with the MicroPower Serial Cable?
Yes. Battery life on Energizer Accu 700mAh NiMH AAA cells is between 5-8 hours on a full charge, with continuous serial data communications between the Visor and a handheld GPS receiver. For comparison, a standalone Visor will run 10-15 hours on a full charge. You can expect battery life to be 50%-100% greater with quality alkaline batteries.

How is the MicroPower Serial Cable different from the Mark/Space Datacord HS or ATL Serial HotSync Cable?
The Mark/Space Datacord HS uses additional circuitry to generate positive and negative voltages that comply with the official RS-232/EIA-232 specifications. Feedback from users is that it works with GPS handhelds, but drains batteries rather quickly, due to the extra power needed to generate the positive and negative voltages.

The ATL Serial HotSync cable was designed for use as a serial HotSync cable. It uses the PC's handshaking lines for power. It will not work with handheld GPS receivers, as GPS receivers do not have handshaking pins available. The ATL cable will work with external modems, although a gender-changer and/or null modem adaptor may be required.

The Mark/Space Datacord HS is on backorder. Can you make me a MicroPower cable quickly?
Unfortunately, I am not in the volume cable business. Please see the Group Buy Updates section above. But if you have unusual connectoring requirements or absolutely need a low-power cable, then you can contact me about building or buying one from me. As witnessed by the extremely long time for me to build the group buy cables, I cannot promise any delivery dates for custom cables.

I have a USB HotSync cable. Can I convert it into a serial HotSync cable?
In short, no. The USB cable is only wired to the USB D+ and D- pins. Meanwhile, a serial cable requires the RXD and TXD pins. Since the connections are made in the HotSync connector, you will likely damage the plastic case while attempting to open up the connector. The best solution is to retain the $20 USB cable as a HotSync-only cable, and buy a $30 Datacord HS instead.

Standard disclaimer: This information is being provided as an educational and informational service for the Handspring Visor community. I do not make any warranties, but I will be happy to help with questions about this project. Please proceed at your own risk!

Last update: 27 March 2001

I have decided to give this cable a name. From now on, I will refer to it as the "MicroPower HotSync Serial Cable". It will be more descriptive than "wac's Serial Cable". I have also added a serial cable compatibility chart to the top of this page. Note: I still personally have no intention of going into volume production, nor will I attempt to obtain trademark protection for this new name.