Tom M'Guinn

Thought I'd post a picture of my newest gadget -- it calibrates the speedometer to read accurately. My speedo was always way off, and only got worse with non-stock tires. I looked into other solutions (moving the needle, calling VDO) but none were ideal. So, with microcontrollers like the Arduino so easy to use these days, I made up this board to intercept the signal from the sensor, adjust it as needed, and feed the adjusted signal to the gauge. Right now, I'm calibrating it via programming, but have the trimmer pot on the board so you can also calibrate on the fly. So far, it's working like a charm (including cruise control), and I've been able to zero the speedo in to the exact mph I'm going. The nice thing about this approach is that it can adapt to any tire/wheel combination. I wasn't planning on selling these, but if there is interest I may put up a step-by-step guide for making them on my rennlist page, with the firmware and schematic/pcb layout. This one is the beta version, sitting in the center console, but the next PCB will be about half the size and fit in a small box behind the dash below the steering wheel. Total cost was under $50 to boot!

Fluidplay

Nice, absolute genius...who in the 944 world doesn't have a speedo that's off. I would definetly like to do this. Thanks Tom

Crazy Eddie

I had the privilege of seeing it in person ...
Really amazing ....

Motosport

Cool... My speedo showing to much is one of those things that always annoys me.. Not only because of the inaccuracy but also because it adds unnecessary extra miles to my car..

I would definitely be interested too, but being completely hopeless when it comes to working on electrics, would it be possible to buy the finished product, ready to install..??

OntarioTurbo

Great work Tom! According to my GPS my speedo is about 10 kms (6mph off).

reno808

For $50 i would i get one. Great stuff. Your looking for new ways to do things and share all of your findings

refresh951

Nice Tom, I would love to see this added to your RL page since I have used all your other "how to's"

Supachink

Tom,

This is awesome! I would love to see something on your page about this. I love the whole wave if tiny SoC PCBs that are coming out and have been looking for an excuse to pick up an arduino... I've been toying with the idea of using my Raspberry Pi to build an XBMC to control the head unit functions in the car, along with using it as a datalogger and piggy back tuner. Good to see there are others on here into tinkerings outside of automotive.

BoostGuy951

Excellent work, Tom. Looks like a well engineered solution to a very annoying problem.

gruhsy

Very nice. I want

nofalls

Nice! Eagle file or schematic and arduino sketch please!

Tom M'Guinn

Ok, let me see if I can pull together a page for my site. I am not planning to sell completed units, but hopefully I can be explicit enough about what I did to be of help. I understand some of our resident vendors may sell a version of this, or something cheaper with similar functionality -- if not, I'm sure we can find a wiki-way to get assembled versions into the hands of the electronics-challenged among us.

m73m95

I switched to a 180mph speedo...and now its dead nuts accurate (according to gps).

However, my I dropped 3mpg with the change Makes me wonder how far off the old 170mph speedo was.

One of the best uses of the Arduino board, I've seen though! Excellent work!

Tom M'Guinn

Hmmm.... interesting, I wonder if the 180's are better? I thought most our speedo's were off based on all the reports here, but we tested Crazy Eddie's 88 'S car and his was also spot on...

333pg333

So Tom do you think the inaccuracies were due to different OD on the tyres or just a malfunction of an old car?