This will be the last teardown video for a while and this time I have a Racal Avionics CDU allegedly from an RAF Nimrod which I obtained some time ago and discovered that it communicates with a host system over standard RS422. Now, thinking I might be able to connect it to my PC or an Arduino or any other type of microcontroller I set about seeing how it worked. Armed with a RS422 / RS485 to USB adaptor and an oscilloscope I powered it up (just needs 28V DC) and probed around to see what I could find. The unit does indeed power up and displays a self test screen. Other than being able to control the screen brightness pressing any of the other buttons did not do anything. So I took it apart to see what was inside…
Model number is 80794/SS302 NATO stock number 5826-99-1603965. It dates from around 1990 and uses a couple of Motorola 680x series CPU’s. It appears to be a serial terminal device. There are no ARINC or MIL-1553 buses on this thing although a look at an EPROM dump suggests that is an option. I was unable to get any serial data out of it unfortunately on the RS422 port and even directly on the UART chip itself. I dumped the EPROMS on the boards which reveals that the device configuration is set via straps connected to the rear panel of the unit. However pin 1 was not indicated and what needs to be done with it e.g tie it to ground or +5V. I didn’t get very far with it but I noticed that the CRT is has a line scan rate of 15.625Khz which is the same as analogue European TV’s. Hmm.
I pulled it apart and too some photos plus made a brief YouTube video which you can see below.
Dear Adrian,
Inspired by your video I bought also a Racal CDU. I just received it yesterday, so there’s not much to tell yet. But maybe in the future some discoveries are mentioned here: http://www.amateurtele.com/index.php?artikel=342 The article is for now only available via the direct link. Since I can’t find a contact form or e-mail address, I used this way to communicate…
Great website! So it wasn’t from a Nimrod as I suspected (I was told it was) I had a suspicion it was from a helicopter, your findings confirms it. It looks the same as my unit albeit with some front panel button differences. The NATO stock number is different on yours so it’s probably the same unit but with different software.
Hope you do manage to get some useful information from it. Mine could have just been faulty; would be interesting to see if yours has any data on the serial port.
Btw I removed the contact form as it was getting hammered by spambots. I’ll have to look at sorting that at some point. Sorry for the late reply; the system should email me when there’s a new comment.
I’ve added my email address to the about page.
Dear Adrian,
Unfortunately my two Racal CDU’s are also not usable except for the selftest. But I found some notes on the internet that the CDU likely uses the ARINC protocol. So I expect that the two data lines are not TTL nor RS232/RS485 signals but ARINC lines. I’ve bought an ARINC converter chip, but I haven’t got the time to test this theory. Well, maybe this insight helps…