UPDATE August 2017:

This article was posted in 2010. I received many thanks from technicians using it in the field to troubleshoot their avionics, and I'm proud of that. This tool is not intended to be something your business should rely upon, and it isn't anything I would ever sell. It is mostly for the small-shop Garmin installer or owner-operator. I checked the number of downloads sometime in 2012 and it exceeded 1,700. I have no idea how often it's been downloaded since, but I still get many inquiries about it, so I will keep this page up. One gentleman a few years ago asked me if I could add engineering units to it, and I had some time so I did.

V2:

This plug-in now requires the included Excel spreadsheet in the same file location, and it will provide engineering units. Modify the spreadsheet with the desired engineering units and re-run the plug-in. Do not change the table headers or column schema or the plug-in may not function. [download]

Introduction:

When got started in avionics I remembered feeling like $5,000+ was a lot to spend for an simple ARINC 429 data reader. Regardless, a 429 data reader is an invaluable tool to have on the flight line.  They’re often scarce and, as I said, expensive.  While tinkering in the shop many years ago, I came up with a cheap, reliable solution for reading ARINC 429 data. I’m offering my solution for free to anyone who will use it and appreciate it.

For less than $300 worth in equipment and my free software, you can read 429 data and troubleshoot avionics data busses.  Simply follow the steps below.

Hack/Tip: In the field there were times I just needed to know if a data bus was active and didn’t care what was on the bus. I’ve used an aircraft headset to 'read' 429 data in a pinch. You can hook up an aircraft headset to a data bus using jumper wires. What you’ll hear is a [very] loud grouping of chirps and buzzes. These are the bits being transmitted on the data bus. The noise will give you an easy indication that your data bus wires are connected and that data is being transmitted. I believe this to be safe for the equipment because, per the ARINC specification, the data bus needs to survive direct shorting and a 150 ohm headset shouldn’t cause any issues. With that said, use this tip at your own risk.

Step 1 – Understand ARINC 429

ARINC 429 is a data bus protocol which the majority of today’s aircraft systems use to communicate.  It’s an asynchronous protocol where one pair of twisted-shielded wires transmits data from a unit to one or more receiver units.  The web is littered with training material.  One that I’ve found useful is published by AIM here.  AIM is a company that makes ARINC 429 test equipment.

Step 2 – Buy a Velleman USB Oscilloscope

I bought a PCU1000 for less than $300, many years ago.  I kept it in my toolbox, and back then it was a go-to tool for crude signal testing. It’s small, inexpensive, has probes.  What more can I say?  It shouldn't be your primary scope, but why not have one?  Pick one up here.

Step 3 – Download my ARINC 429 plug-in for the Velleman PCSU1000

I programmed this plugin [download] specifically for the PCSU1000. You will need a windows-compatible computer with .net installed.  I've tested this program with Windows 7 [UPDATE: works with Windows 10].

Setp 4 – Connect the Oscilloscope to the ARINC 429 databus and read the data

Run the Velleman software and connect the CH1 probe to the data bus wires.  The “A” leg of the data bus (typically the white wire) needs to be connected to the center contact on the probe and the “B” leg of the data bus (the wire with the blue stripe) needs to be connected to the ring of the probe. What you’ll see on the screen is a wave representing the voltage levels as the data is being transmitted.  Now, start the plug-in.  The status at the top should read “Configuring PCSU1000 Settings…”  This means that the plug-in is setting up the frequency and voltage per division on the scope for receiving ARINC 429 data.  Do not change these settings.  If you do, simply select “Reset PCSU” to put the settings back.

The buttons have the following functions:

[Run / Pause]

When the status indicates “Running” the data reader is displaying unique labels as they are received.  Pressing will pause the display allowing you to scrutinize the data.  Pressing again will continue the read operation.

[Clear]

This erases all the existing data.  This is important when switching to a new data bus or when looking for a ‘single-shot’ label.  The labels in the display are maintained until the this button is pressed.

[Record]

The PCSU1000 scope has a small buffer. Pressing will allow you to record a few seconds of data and see the exact order and frequency of the labels being transmitted.  Press and wait for the data to be displayed.

[Bus Speed]

This switches the receiver between low speed data (12.5 kHz) and high speed data (100 kHz).

[Export]

Press this to create an excel spreadsheet of the data on the display.

[Reset PCSU]

This button initializes the frequency and volts per division on the Velleman scope. This function is executed automatically whenever the plug-in is opened.  Use this button to restore the settings if you inadvertently set them to something else.  The scope must be configured in order for the buffer to be filled properly.

Conclusion

I’ve given this software out to many technicians and engineers over the years and it always makes me happy to hear that they used it to troubleshoot or design.  It’s not a high-end product like those made by AIM, Condor or BusTools, but it will do 95% of what you need at none of the cost.  Enjoy it and contact me if you have any issues.