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Aurduino Powered Tach

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Wondering if anyone has replaced the guts of their stock tach with more modern innards.


I have a carb'd LS2 and my tach cuts in and out above 4000 RPM.  Does it with 2 different 280z tachs.  I know it isn't the MSD box cause my speedhut shift light and LM2 tach adapter work fine.


I've tried everything I can think of to fix it:  pull up resistors, transistor based tach drivers, in line resistors, in line and shunt capacitors, powering tach right off the battery, etc.  I even went so far as buying an inexpensive tach and putting the guts of it behind the stock face.  That actually works but it doesn't match the range exactly so the reading is off.  


The next step is Autometer gauges, which has its obvious benefits, but I would have to do the whole cluster and figure out where to mount turn signal and high beam indicators.


My idea is an Aurduino microcontroller and GM stepper motor.  Will model what this guy has done 




Figure I can complete replace the guts for $20 in parts.  Should be easy to calibrate exactly and will have a modern response time.  A slight side benefit is it might save a couple of pounds over the stock mechanical unit.


If this works out my next project is adapting the stock LS2 temp sensor to drive the stock temp gauge as well as  fan controller with adjustable hi/low set points and a warning light.  From there seems like one could convert a stock speedo from cable to electronic pulse.  Only problem there might be the odometer.





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Being a huge arduino person myself this sounds awesome. But you would have to figure out the pulses that your MSD puts out to translate that into stepper motion. Unless they've already written a library for that translation?


I will now be ordering me one of those and seeing if I can interface it with the ls1 ECU and read off the tach pulses.

Edited by CableSrv

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Speedhut makes quality stuff.  I have their shift light with digital tach.  But with the exception of the exhaust note my car looks totally stock.  I even kept the stock shift knob when I made an offset shift lever.


Also I'm not so sure about replacement gauges being easier and they definitely won't be cheaper.


The Arduino stepper motor is going to be easier than I thought.  Some guy already wrote a library of utilities to drive the Switec stepper motors. 




The Arduino can drive the units directly, no driver circuit needed.  The web is full of code for digital tachs, just need to find the code to count the pulses and use that to drive the Switec library. 


Figure I can get a $14 Arduino micro and already bought 6 stepper motors off amazon for $14.  All I need to do is mount the two together and build a sheet metal frame to mount it to the tach face.  If you have ever had a stock tach apart you know what I mean.  Will then need to calibrate the sweep into the code so the needle registers correctly.  The web is full of Arduino code to make a pulse generator.  Can use that as a tach driver to do the calibration, then verify it in the car with the Speedhut shift light/tach.  Once I get it working can switch to an Arduino mini for $10 that is even smaller


The Arduino can be powered right off the car 12V and the shaft on the stepper motor is bigger in diameter than the stock Datsun unit.  That means the stock needle can be drilled out to work.


Just need to find the time now.


I'm telling you someone could make money converting stock speedos to work with electronic pulses.

Edited by zdlite

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Hah.  Looks like it only took me 3 years to get around to doing it but got the tach working.  Turned out super simple.  A $4 Chinee Nano knock off, a couple bucks Switec stepper motor, the same ones GM uses, an optoisolator that I had from an Arduino starter kit a small prototype board and two resistors.  The thing is super stable now and I can easily adjust the level of filtering to smooth the response time.  I was also able to calibrate it exactly


I got lucky in that the stock tach had this nice aluminum cradle that mounted the circuit board easily.  I had some left over brass screen door plates that I soldered to the stock cross piece than drilled and tapped to mount everything.


I did build a tach signal generator out of a second Arduino that I used to debug this thing.  Should prove handy to test and calibrate tachs in the future.


One other nerd feature is the nano had multiple excess pins.  If I wanted too I could easily hook up some different colored LED's inside the tach housing and make the tach change color with RPM.  It would just take a few lines of code to add a shift light, although adding some sort of user interface to set the trigger point would be more work.


So only $10 in parts and probably 200 hours of my time saved me from having to buy a whole set of Autometer gauges.  Deal.


Next project is a fan controller with a wifi link for external temp readings and fan set points.





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