darryl ramm’s blog

I like my Cambridge 302 electronic vario/logger, however there is a bug in the Cambridge 302 where flight logs are apparently OK but the security record is invalid. What I describe here is a way to use SeeYou Mobile running on a PDA connected to the 302 to clear the memory log to avoid recurrence of the problem.

If your 302 has this problem it does not matter if you download the flight trace using the Cambridge “300 Utility” software on a PDA or a Windows PC, or the Datacam2 and Valicam2 MS-DOS utilities, or something like Naviter ConnectMe or SeeYou. All files downloaded will have invalid digital signatures. If you have this problem the Cambridge utilities will show a “Security Fail” error when the download completes.

The problem is apparently related to the flight log memory filling up and wrapping around, and overwriting previous traces, which it is supposed to do. However when this happens the calculated log signatures (IGC G-records) seem to be incorrect, even though the flight trace data itself is valid. This makes the IGC flight trace useless for FAI badge, record and Online Contest purposes. This may not affect all 302s or maybe not affect them each time the memory wraps, but if you do see this problem all your future flight traces will also be invalid. The workaround is to erase the flight log memory, at least then future flight traces will be valid, however of course this means you loose any current flight traces. I’ve had this happen to two different  302 varios and in both cases, clearing log memory made the problem go away.

As a preventative measure then it seems a good idea with a Cambridge 302 to periodically erase flight log memory before it has a chance to fill up. It may also be a good idea to run a lower log rate so the memory fills up less rapidly.

The only way to clear the memory is to attach a terminal emulator to the 302 serial port, type CTRL-C to put the port in command mode and at the cmd> prompt  type CLEAR LOG.

I fly with Naviter SeeYou Mobile and the nice thing is it is possible to clear the 302 log memory using the simple terminal emulator built into SeeYou Mobile. So there is no need to run a separate terminal emulator program or connect a laptop with HyperTerminal etc.

To get started connect the PDA to the Cambridge 302 and make sure they are talking to each other (you get the “Cambridge 302 Connected” pop-up message  on the main SeeYou Mobile screen). Then in SeeYou Mobile go to Settings>Hardware>Terminal. This Terminal screen is shown in the screenshots on this page. Click on the the keyboard icon, this will let you type a string into the top text field. Then click on the Send button to actualy send this string to the Cambridge 302.

When you first bring up the Terminal screen the 302 will be spewing NEMA GPS data to the terminal window.  The secret is knowing that if you type HEX(3) into this field SeeYou Mobile will interpret this as ASCII-3, aka CTRL-C and send that to the 302. Thanks to the folks at Naviter for pointing out this undocumented feature.  After the CTRL-C is sent you will see the cmd> prompt in the terminal window.  Then it’s trivial to type CLEAR LOG and click on the Send button again. The Cambridge 302 will pause for ten seconds or so as it clears memory before returning another cmd> prompt. The next time you want to do this you’ll find the HEX(3) and CLEAR LOG strings saved in the pulldown field at the top of the terminal page.

I do not believe this problem is related to problems with downloading flight traces from older Cambridge GPS model 20 or 25. I do not know if the Cambridge 302A (logger only model) is also affected by this problem,  they may as the 302A is basically a stripped down 302.

BTW all the command port commands and relevant information are described in the Cambridge 302 Dataport User’s Guide available here.

And all this assumes there is not something else going on, if you are having other problems, check the digital seal on the 302 is intact. If you have a 303 navigation display connected you will see a  message at power-up saying the seal is OK.  You can also check the seal by pressing the control knob slowly ten times to go to screen 10 and then rotating the knob and you should see  “gOOd SEAL” in the 303 display.

R-Track Technologies aka Cambridge Aero Instruments are currently testing different FLASH memory chips in the 302, I have had my 302 upgraded with this change but I’m not sure how long it will take to be comfortable that this has addressed the problem. The problem may also be a software bug, I’m not sure it is really fully understood.