Custom Data Writer Board For 1996 Plane’s GPS

KLN89B GPS data card reader/writer

[Dmitry Grinberg] recently bought a Cessna 150 that contained an old IFR-certified GPS from 1996, the KLN89B. The GPS unit contains a database which by law has to be kept up-to-date for IFR flight. The problem was that, while Honeywell still supplied the data in electronic form, [Dmitry] had no way to update the GPS. The original ways for doing it are either no longer supported, too expensive and a pain to do, or not available to him due to the way his GPS was installed.

Two of those ways involved removing a data card which can legally be slid out of the GPS’s front panel. The data card is what stores all the data but it’s a proprietary card and there’s no reader for it. [Dmitry]’s solution was therefore to make his own reader/writer board.

Reading the card using the STM32F411 dev board
Reading the card using the STM32F411 dev board

Examining the card, and another he’d bought off of ebay, he was able to use the datasheets for the components to work out the card connector’s pinout. Starting from there he wired it up to an STM32 development board and proved that he could reliably read the card’s contents.

Having done that, he next designed his reader/writer board around the 5V AT90USB646 Atmel 8-bit AVR RISC-based microcontroller. Also on the board is a 12V boost converter and a connector for plugging in the card.

While his board was being manufactured he turned his attention to the data itself. Honeywell still supplied updated data in digital form as a Windows EXE file. A quick examination showed it to contain a ZIP file, and in no time he had the database itself. But it wasn’t as simple as that. Most of it turned out to be encrypted, and from more experimenting, he’d learned that the data was supposed to be decrypted before being written to the card. However, [Dmitry] was up to the challenge and after a few days hard work, found that the encryption was fairly simple and based on applying CRCs starting with a key that was in the data itself. After a remaining troublesome 8 bytes, he had the proper updated data for writing to the card.

Once his manufactured board arrived, he added the microcontroller and other components and had it reading, writing and erasing the card in no time. While he has made the schematic and all software available on his website he also gives plenty of disclaimers, understandable, since this is for a GPS in a plane. But even if you’ve no need to use it, you’ll also find on his website [Dmitry]’s very detailed write-up of this project.

KLN89B GPS data card reader writer schematic
KLN89B GPS data card reader writer schematic

[Dmitry]’s also no stranger here on Hackaday. His projects have ranged from an encrypted USB bootloader for AVRs to a greeting card made from a CD case that plays full songs to an 8×8 matrix LED pendent encased in epoxy.

37 thoughts on “Custom Data Writer Board For 1996 Plane’s GPS

  1. He used to do a lot of Palm OS software. All his Palm stuff is freeware at

    Too bad he never got around to coming up with a way to add WPA2 support to Palm devices with WiFi. Palm had developed it but for some idiot reason chose to not release it, so Palm OS devices are stuck with WEP or at best WPA.

  2. This is a wonderful solution to an on going problem.

    Manufacturers abandoning equipment. The KLN89’s were very expensive (like $5k) when first available. To replace it with another certified GPS unit would be about the same amount. The C150 is only worth about $25K, so for 20% of the value of the aircraft, the GPS can be certified for IFR use.

    This fix allows the GPS in the aircraft to be not quite as good as his phone :-).

    Since airport identifiers and airport configurations change ever 56 days, I am sure the old database was barely usable.

    1. Approved instrument costs are now why we have the wonderful rules regarding Electronic Flight Bag equipment and can use portable electronic devices at our own discretion in GA. An iPad is a helluva lot cheaper than most GPS/Radio panels. That being said, I like that this guy is keeping his existing equipment legally functional.

          1. Some Osram zigbee bulbs that are just being used as normal bulbs.

            Some Maplin MR16s, a Wilko pretty LED filament bulb in my study and a couple of poundland bulbs.

            I think there’s a Hue Lux and a 10 year old color cycling bulb somewhere?

          2. From Wikipedia: “The Centennial Light was originally a 30-watt or 60-watt bulb but now is very dim, emitting about the same light as a 4-watt nightlight.”

            If that was a CFL or an incandescent bulb in my house I’d recycle/trash it. If it were a LED I’d take it apart. ;)

            I’ve heard that they run that ‘amazing 100+ years old’ bulb at a lower voltage.

            Most of my bulbs are Sylvania. The CFLs seem to last forever only breaking because of human error or when low outdoor temperature fries them in the winter. Mostly LEDs now.

      1. Technically it’s no longer legal because it’s a piece of certified avionics that has been modified aftermarket or, as the FAA refers to is, “tampered with”… you need a maintenance service accreditation to make these changes legally and then go through a process of re-certifying the equipment per unit to place it in an aircraft as in-service avionics. Dmitry states in no uncertain terms here(although the HAD article, not written by him, implied different), that this device is NOT in service on an aircraft and was a bench experiment on salvage avionics to see if he could update the data without the legacy programmer.

      1. Layout looks fine to me.

        I’m sure that addy771 is offended that you didn’t shell out for stencils for a one-off board. Because you must be flush with cash after buying a freakin’ airplane :)

      1. But the connector is there behind the GPS right? I understand it is not currently installed to be accessible all the time, but since the GPS slides out, can’t you just pull it out, power it outside of the plane, and update it via rs232 ? Without permanently modifying the plane , aren’t those pins accessible? I mean, that seems to be the normal way to update. Congratulations on getting it done for sure , and now you have a permanent solution, but surely you could of gained access to those pins without breaking any rules.

      2. Surely if the RS232 port exists on the unit ( which AIUI appears to be the case), why could you not use it to do the upgrade with a temporary connection, avoiding the issue of any permanent mod that might affect approval?

          1. What echo is saying seems to be that you should, if it’s not too much of a PITA or too expensive to do so, see if you can get it certified so it’s legal to use if you choose and (possibly) for others to use for the same equipment.

      1. I see. The HAD article implied it was necessary to make this modification to update a legacy GPS receiver’s data to comply with IFR regs… which is where the confusion on my part starts, since they don’t like you messing with in-service stuff like that without maintenance service accreditation, if at all. It does not have to comply with IFR regs sitting on a desk, being not-in-service. So… that all makes sense now.

  3. Love the hack, but bad idea to use. Even something as simple as changing a split cotter pin on my r22 doors to a pin with clip is a big no no. God forbid he ever crash, the easy way out for flight investigation is to blame the hacked card and self decrypted hacking. This would void his insurance as it’s an easy argument for an insurance company, thus opening up the pilot to liability of any damages causes by the crash. It sucks, but it’s reality, that’s why onboard equipment is expensive, to pay for the exhaustive testing. I have been involved in a design of some equipment that never went further than the cost of testing.

    1. Yeah if you do it without documenting and getting approvals. However if you make a modification, just document it and get it approved at your local ACO or if there is a mod shop nearby, ask them who their DER or subject matter UM of choice is and get it approved.

      1. If you decided to use this card for flying would it cost a lot of cash to get it certified or would they just flat out refuse certification as it was a hacked card? kudos on the hack though it really is great.

        1. I am not certified for aircraft maintenance, but AFAIK there are FAA cert levels of avionic tech who can and will sigh off on modified electronics; some are braver, charge more, or are better insured than others. It is like finding or fabricating a substitute engine or airframe part and getting it certified for use outside of the experimental realm. You pay expert prices to those who have earned the cert but it is not so very pie-in-the-sky.

          1. Yeah I suppose the cash you pay is to cover the expert’s risk is signing off your work. If he/she got it wrong and you crashed because of the mod then it is their neck on the chopping block. I understand now. Thanks!

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