The rallyduino lives

[Update: The code or the rallyduino can be found at:]

Amidst a million other things (Today is T-1 days until our little bubs technical due date! No news yet though) I finally managed to get the rallyduino into the car over the weekend. It actually went in a couple of weeks ago, but had to come out again after a few problems were found.

So, the good news, it all works! I wrote an automagic calibration routine that does all the clever number crunching and comes up with the calibration number, so after a quick drive down the road, everything was up and running. My back of the envelope calculations for what the calibration number for our car would be also turned out pretty accurate, only about 4mm per revolution out. The unit, once calibrated, is at least as accurate as the commercial devices and displays considerably more information. Its also more flexible as it can switch between modes dynamically and has full control from the remote handset. All in all I was pretty happy, even the instantaneous speed function worked first time.

To give a little background, the box uses a hall effect sensor mounted next to a brake caliper that pulses each time a wheel stud rotates past. This is a fairly common method for rally computers to use and to make life simpler, the rallyduino is pin compatible with another common commercial product, the VDO Minicockpit. As we already had a Minicockpit in the car, all we did was ‘double adapt’ the existing plug and pop in the rallyduino. This means there’s 2 computers running off the 1 sensor, in turn making it much simpler (assuming 1 of them is known to be accurate) to determine if the other is right.

After taking the car for a bit of a drive though, a few problems became apparent. The explain them, a pic is required:

The 4 devices in the pic are:

  1. Wayfinder electronic compass
  2. Terratrip (The black box)
  3. Rallyduino (Big silver box with the blue screen)
  4. VDO Minicockpit (Sitting on top of the rallyduino)

The major problem should be immediately obvious. The screen is completely unsuitable. Its both too small and has poor readability in daylight. I’m currently looking at alternatives and it seems like the simplest thing to do is get a 2×20 screen the same physical size as the existing 4×20. This, however, means that there would only be room for a single distance tracker rather than the 2 currently in place. The changeover is fairly trivial as the code, thankfully, is nice and flexible and the screen dimensions can be configured at compile time (From 2×16 to 4×20). Daylight readable screens are also fairly easily obtainable ( is the ultimate small screen resource) so its just a matter of ordering one. In the long term I’d like to look at simply using a larger 4×20 screen but, as you can see, real estate on the dash is fairly tight.

Speaking of screens, I also found the most amazing little LCD controller from It has both serial and I2C interfaces, a keypad decoder (with inbuilt debounce) and someone has gone to all the hard work of work of writing a common arduino interface library for it and other I2C LCD controllers ( . If you’re looking for such a LCD controller and you are working with an arduino, I cannot recommend these units enough. They’re available on eBay for about $20 Au delivered too. As much as I loved the unit from Phil Anderson, it simply doesn’t have the same featureset as this one, nor is it as robust.

So that’s where things are at. Apologies for the brain dump nature of this post, I just needed to get everything down while I could remember it all.

3 thoughts on “The rallyduino lives”

  • Just came across your blog while googling ‘minicockpit’ (you are hit #5!) cos I’m having some problems getting mine to work. I bought mine second hand with no sender, and bought a terratrip sender (the speedo cable pulse generator type) to use. Unfortunately, the calibration number (211) is below the minimum allowed (300)! Where did you get your sender from?
    As an aside, I’ve heard on an internet forum (therefore it’s gospel…) that there is a guru somewhere that can modify minicockpits. Do you know anything about this?
    Cheers (and congratulations!)

    • Hey Sam,

      I’m not really familiar with the speedo drive senders I’m afraid as I’ve always used the wheel probes instead. There are a few different types of terratrip senders though and not all are compatible.
      To answer your 2nd question however, yes, there is a guy around who modifies the software (and hardware in some cases) of the VDO to give it a few extra abilities. He’s done the 2 units that we have. I don’t have his details on me at the moment, but I’ll dig them up over the next day or so and let you know.

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