The RV Journal

Interfacing the iPAQ with the Navaid Autopilot

(This page has numerous updates because the iPAQ installation was a process of evolution over a period of several months during the early development of the AnywhereMap system.. Matter of fact, the old iPAQ 3765 was eventually replaced with a Dell x30. Obviously this means much of the material presented is out-dated, but hopefully a careful reading will still be useful in gathering ideas for installing the iPAQ with Anywhere Map software)

Part One

It seems that a very satisfactory configuration of the Anywhere Map system is now in place in my RV-6. The main objectives were to achieve an installation with minimal loose cables and with a solid interface with the Navaid autopilot. The first iteration included the Sentinel compact flash card GPS; very quickly I realized the external antenna was going to be necessary to get the performance of the Sentinel up to acceptable level, even under the full canopy of the RV-6. Without the external antenna, GPS lock was occasionally lost in turns and climbs (the RV-6 is capable of climbing with impressive deck angles), but the least satisfactory aspect was the poor altitude readouts that often were hundreds of feet in error. The external antenna greatly helped the altitude performance and GPS lock reliability, but now there was another cable dangling from the panel.

For hundreds of hours the Lowrance Airmap 100 has provided stellar performance in the RV-6 with only the built-in antenna, and many of those hours it faithfully drove the Navaid autopilot. The unit is mounted on the panel in a cradle and fed with onboard power. Curiously, the Lowrance developed a tendency to lose satellite lock when the iPAQ/Sentinel was mounted beside it and running. Seems the Airmap is definitely capable of GPS envy when faced with the possibility of neglect! The original intent was to remove the Airmap and retain it for emergency use, but the less than perfect performance of the Sentinel caused me to rethink the installation.

Much has been written about the fragility of the serial connector on the iPAQ and the resulting problems with the Anywhere Map (AWM). In spite of those warnings, I decided to try incorporating the excellent receiver in the Lowrance to drive the AWM, and also put the iPAQ in the Navaid loop. The Lowrance is wired to the Navaid via the serial port on the Airmap, so provision had to be made to insert the iPAQ into the Navaid harness. I also wanted to be able to quickly revert to the original configuration in case the iPAQ went out to lunch at an inopportune moment (actually I am more worried about the Windows-based architecture....). I intend to explore ways to solidify the cable connection at the iPAQ; the cable connector fits quite snugly at this time but I am concerned about a passenger hitting it while boarding and damaging the iPAQ.

Update: Here are photos of the keeper I devised to prevent the serial cable from dropping out of the iPAQ connector.

A small piece of scrap 0.016" 6061 aluminum was cut, trimmed, and bent into the configuration shown. It was then attached to the bottom of the expansion sleeve with a single pop rivet. The slot is sized to fit snuggly around the cable just below the connector.

Here is the cable securely attached to the iPAQ. Some sort of arrangement such as this is necessary because the retention hardware on the cable connector is very small and flimsy.

The cable is inserted into the slotted clip, and the iPAQ is slid into the expansion sleeve. I removed some material from the top of the RAM cradle so the iPAQ could be inserted into the top of the sleeve without removing it from the cradle.

A DB-9 connector (available from Radio Shack) was attached to the panel of the RV-6. The connector was inserted in the data line from the Lowrance to the Navaid; pins 2 and 3 are the only pins used since these are the "data received" and "data transmitted" pins in the serial protocol.

A DB-9 plug was wired with pins 2 and 3 jumpered; when this plug is inserted into the panel connector, the data feed is routed from the Lowrance to the Navaid in the original configuration.

The mount used for the iPAQ is from RAM. The cradle is RAM-HOL-CO1, and the  ball/socket mount is RAM-SB-190. These are available from gpscity.com.

A serial cable was procured for the iPAQ 3765 (Compaq part number 236251-B21). When the plug is replaced with the serial plug on the iPAQ cable, NMEA data transmitted by the Lowrance goes to the iPAQ, and data returned by the iPAQ/AWM goes to the Navaid. The iPAQ then is able to find its location courtesy of the fine receiver in the Lowrance, and the Navaid gets the benefit of the cool navigation features of the Anywhere Map. The Navaid appears to be perfectly happy with the data it receives from the AWM and the Smart Coupler functions just as it does when coupled to the Lowrance.

(right-click on the graphic below to download a larger version for printing)

(note: if the iPAQ is not powered by the plane's power bus, it may be necessary to add a ground connection on pin 5)

I decided to mount the external antenna for the Lowrance on the glareshield in order to milk the system for all it was worth. The approach portion of the AWM provides neat altitude features and I wanted to utilize them as much as possible. I found that the Lowrance altitude data was indeed enhanced by the better view provided by the external antenna and altitude readouts seem to average within 15-40 feet of altimeter readings.

There is a minimum of extraneous cabling in the cabin; the serial cable is only a few inches long and goes directly to the DB-9 panel connector, and the power cable for the iPAQ runs inconspicuously to a power outlet beneath the panel. The RAM mount with iPAQ cradle is mounted beside the Lowrance in easy reach and eyesight, and a fat, easy-to-grip homemade wood stylus is velcroed to the side of the cradle.

This appears to be a very workable interface of the iPAQ to the existing GPS/Navaid system. The Lowrance will operate for many hours on battery power if necessary, the iPAQ is good for a couple of hours or so, and the system can be quickly reconfigured back to the original setup if the iPAQ is unavailable.

The Anywhere Map software on the iPAQ computer is not yet a perfect combination, but the features present now are just a preview of the exciting options that no doubt will be forthcoming. Even with the Approach phase of the software in early development, the Anywhere/iPAQ combo is an impressive addition to the  RV panel; if the pilot already owns an iPAQ and suitable GPS receiver, the Anywhere Map has to be one of the best navigational bargains available.

Update on flying the Anywhere Map interface with the Navaid

After flying with the Anywhere Map/Navaid combination, I have noticed a couple of issues with this combination. The first inkling I had that the AWM was steering the Navaid differently than the Lowrance Airmap was when I noticed the RV-6 "snaking" gently as it proceeded along the route. I have become accustomed to seeing the Lowrance signal hold the Navaid to within three or four hundredths(!) of a mile of course centerline with heading corrections so minute they are nearly imperceptible. It appears that the AWM has a course deviation resolution of no better than one tenth of a mile either side of centerline. This results in the plane scalloping along the course as it corrects in 2/10th's mile increments. While this is not a serious issue, after being spoiled to the near perfect tracking performance of the Lowrance, it is disappointing to have the plane gently turning back and forth as the Navaid is guided by the much less precise CDI of the AWM. I have also seen the CDI in AWM suddenly make a minor change as the map redraws when zoomed in or out; this results in a heading correction being transmitted to the Navaid.

Update to the Update (4/17/05)

The Navaid was replaced by the vastly more capable EZ-Pilot from Trio Avionics. Unfortunately, as of AWM version 1.6.2, standard NMEA data protocol is not provided by AWM and it is unable to drive the EZ-Pilot. Users of the Navaid can still use AWM since the Navaid only needs course correction data.

Update; Installation of Garmin GPS35-HVS receiver

The previous shortcomings of the AWM software for driving the Navaid prompted me to install a Garmin GPS35 receiver that is dedicated solely to the iPAQ. This enabled me to move the Navaid duties back to the Lowrance Airmap 100 which does a stellar job of driving the autopilot.

The GPS35 is a self-contained twelve channel GPS receiver and antenna. I purchased the HVS version from gpscity.com that can be used with an input of 6-40vdc, and comes with a 15' cable with bare wire ends. The unit is about the size of a computer mouse, and is the similar to the GPS35 sold by Control Vision in their AWM bundles. The bare wire version worked fine for me since I already had the interconnections for the iPAQ in place. The red and black wires were attached to 12v and ground respectively, and the white wire went to the data input pin on the DB9 connector I had previously installed for the iPAQ serial cable. The receiver was attached to the glare shield with double-sided tape unobtrusively  beside the Lowrance antenna.

I have found the GPS35 to be a fine receiver which achieves satellite lock almost immediately. It was already configured for 4800 baud serial output so no further configuration was necessary. Now the Lowrance driving the Naviad and the GPS35 driving the iPAQ are independent and provide a great cross-check on each other.

Part Two

(Here is a copy of a post I sent to our local group, The Tennessee Valley RV Builders Group, on my initial impressions of the Anywhere map)

I now have a few hours flying with the Anywhere Ipag-based moving map software, enough to begin forming some opinions. The mount is by RAM and the cradle is designed just for the iPAQ.

Here is how it is shaping up so far:

1) Overall, this is a VERY impressive piece of software! I don't have personal experience with the Garmin 430/530 maps, but I can believe the claims that in a graphical sense, this map is more impressive with more capabilities than the Garmin map.

2) The iPAQ screen is proving to be very readable in most cases, and readable enough in the remainder of instances. Polarized sunglasses are not the best choice when viewing reflective screens like the iPAQ, but I can still easily read the screen through the glasses even though they cut down the brightness.

3) The amount of features included in the mapping software is mind-boggling! I haven't thought of one bit of info I want in a map that isn't included. There are still some menu related issues where the software can be tweaked, but the company seems to be aggressively pursuing refinements on nearly a daily basis; software updates are downloadable from their website.

3) The learning curve is pretty steep, just as it is with any complex software. However, it is easy to just fire up the system and let it show the surrounding area, but the menus are multilayer, and the deeper you probe, the more interesting stuff you find.

4) If there is a downside, it is the interface, and this is where the b$$g box$s like Garmin are probably superior (though I have heard you better spend some quality time with the 430 manual!) The first time I used the Anywhere Map, the air was bumpy and I found it nearly impossible due to my inexperience to program on the fly. However, as I have gotten more accustomed to the system, I have found shortcuts to a lot of stuff; this reminds me of learning a new workflow for digital vs film photography....you just have to acclimate to a new way of thinking. Most flight planning can be done on the ground if I just think far enough ahead.

Here is the iPAQ with the Sentinel flash card GPS receiver mounted in the compact flash sleeve. The external antenna is not shown.

5) For IFR pilots, the new Approaches feature is AWESOME! It is still in beta with a lot of bugs and incomplete info, but once the kinks are ironed out, this is going to be an incredible system for way under $1000. No, this system will never be TSO'ed, but..........I put the course in the VOR radio, the approach plate in my lap..........and fly the Anywhere iPAQ! Being able to simply "fly the little plane" down the big fat red approach course (including procedure turns and holds, even shows arrows for the correct direction in the holds, altitude stepdowns, and ALL fixes....even GPS fixes <grin>) on the map is just..........cool.

6) If you already have an iPAQ PDA, or can use one for everyday use (mine is absolutely essential with all my appointments and booking info), the Anywhere Map system has to be the biggest bargain EVER offered in avionics.

7) Here is the neat part; this system can be updated ad infinitum. The iPAQ is just the display and processor for the software which no doubt will see some great new capabilities down the road. The charts are updated on a 28 day cycle for just $115 per year; compare that to the cost of keeping a full set of Jepps or NOS plates, low altitude enroute charts, and sectionals. Plus....there is info on the Anywhere map that doesn't exist on gov't charts such as temporary TFR's.

Sam Buchanan

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Table of Contents 

RV6 Home

Who is Sam? 
The Hangar 

Getting Ready to Build 
     Odd 'n Ends 

Building the Tail 
     Horz. Stab Log 
     Vert. Stab Log 
     Rudder Log 
     Elevator Log 
     Uh-Ohs 

Building the Wings
     Wing Spars
     Wing Assembly
  Flaps
  Ailerons
  Fuel Tanks

Building the Fuselage

The Finish Kit

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