# Arduino Tach Hack



## dtbaker (Jan 5, 2008)

cool for EEs.... but who wants to completely rip apart the dash to get to this stuff?!


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## etischer (Jun 16, 2008)

Well, in my case, it's the only way to get a functional tachometer. I also wanted to avoid having black boxes velco'd onto the dash =)


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## Weisheimer (May 11, 2009)

The serial LCD just looks like it BELONGS there...as have other projects you've done on the car.

I think it is a great way to utilize what came in the car with something new and useful.


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## Jozzer (Mar 29, 2009)

Nice work.
Fortionatly I have a Soliton which can drive the dash directly, but I still have an arduino watching the motor temp, controlling the heater/fans, and logging data from the controller and Cycle Analyst.


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## coulombKid (Jan 10, 2009)

etischer said:


> I hacked open my gauge cluster, and thought I'd be able to run my tach just like an analog volt meter. Turns out it is a stepper motor driving the needle movement, so I bought an Arduino to drive it.
> 
> I also decided to add an LCD display for Battery voltage and motor current.
> 
> The data (RPM, Amps, Volts) is being streamed over the serial port from my drive inverter!


I've done the same thing with the Parallax Propeller but my digital display doesn't look as cool. Do you have a source/PN for that?


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## etischer (Jun 16, 2008)

They have some pretty cool full color touchscreens too..

here is the one I got, only $10
http://www.adafruit.com/products/181



coulombKid said:


> I've done the same thing with the Parallax Propeller but my digital display doesn't look as cool. Do you have a source/PN for that?


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## Weisheimer (May 11, 2009)

etischer said:


> They have some pretty cool full color touchscreens too..
> 
> here is the one I got, only $10
> http://www.adafruit.com/products/181



So it isn't serial after all. 
I have the bad habit of seeing things as I imagine that I would do them. No ribbon cable, so not parallel!
You can see where that gets me 

And as an aside. Susan glanced at the laptop screen when I was looking at this.
She asked if it was a bomb......


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## Nashblackcat (Apr 15, 2012)

Weisheimer said:


> So it isn't serial after all.
> I have the bad habit of seeing things as I imagine that I would do them. No ribbon cable, so not parallel!
> You can see where that gets me
> 
> ...


Hello guys. I noticed your post and wanted to also mention that you can add to that type of display to make it serial (i2C or SPI).

http://www.adafruit.com/products/292

Adafruit also sales some nifty positive/negative *RGB* LCDs that have a USB/Serial backpack option. 

Neg. http://www.adafruit.com/products/784
POS. http://www.adafruit.com/products/782

I did have one question. So the serial data is coming right off the drive inverter?


Kevin G


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## ga2500ev (Apr 20, 2008)

Nashblackcat said:


> Hello guys. I noticed your post and wanted to also mention that you can add to that type of display to make it serial (i2C or SPI).
> 
> http://www.adafruit.com/products/292
> 
> ...


A bit pricey at $25 each. I'm not sure I like an RGB backlight that much.

ga2500ev


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## PThompson509 (Jul 9, 2009)

How did you determine that it was a stepper motor? All I saw for my VDO tach (for a Porsche 914) was that it needed a pulse input....

BTW, I gave up on the idea of driving my gas gauge, and will be putting in a similar LED gauge. Will post that hack when it is done.

Cheers, Peter


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## etischer (Jun 16, 2008)

The motor for my tach has 4 wires, if it were a simple analog meter it would just have 2. I would assume your 914 tach has an analog motor. 



PThompson509 said:


> How did you determine that it was a stepper motor? All I saw for my VDO tach (for a Porsche 914) was that it needed a pulse input....
> 
> BTW, I gave up on the idea of driving my gas gauge, and will be putting in a similar LED gauge. Will post that hack when it is done.
> 
> Cheers, Peter


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## DJBecker (Nov 3, 2010)

PThompson509 said:


> How did you determine that it was a stepper motor? All I saw for my VDO tach (for a Porsche 914) was that it needed a pulse input....


The tach input is typically a negative pulse per spark. A specialized chip converts that input into gauge-driving signals.

The tachometer and speedometer gauges themselves are often quadrature coil meters, which are much like two pole motors. The needle position is set by the "sine" and "cosign" current ratio in the two coils, independent of the voltage or precise current. The advantage of this design is that the meter only needs to be aligned during manufacture, and it retains that alignment independent of environment and aging.

A fuel gauge may use a similar design, or may be an intentionally slow-responding thermal gauge.


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