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Author Topic: Speedometer signal source?  (Read 1004 times)
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Hi folks, new to this, though not new to electronics or programming.  I've been working on some custom gauges and I'm at the point where I want to start testing some concepts and the Arduino looks like it will do what I need.  I originally bought it as an impulse buy when purchasing other components, I figured it would make for some neat projects with my kids and I (they have been working with snap-circuits and similar kits).  Well I'm seeing all sorts of projects in my near future, but I need to get this one figured out.

So I have some speedometers from Harleys, I want to use the Arduino to simulate the output of the speed sensor (and later tachometer).  Tone() looks like it will do what I need, the problem is, how to hook it up.  The speedo has power in, when I apply 12v to it, I have 9+v coming out through the red and black leads going to the hall effect sensor.  White would be the signal.

While I can plug the white into a pin affected by tone() for the + signal to the gauge, how would I ground the Arduino to the speedo, just tie it in ground to ground?

Thanks!
Trip
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nr Bundaberg, Australia
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just tie it in ground to ground?
Yes, grounds always have to be connected.

Will the 5v signal from the Arduino be enough, it's obviously used to 9v. It probably will be but if not you can raise the Arduino level with a transistor.

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Rob
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Rob Gray aka the GRAYnomad www.robgray.com

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Well, the speedo takes 12v in (orange/white is 12v+ black is -) and then sends  what my meter tells me is 9v out to the red and black leads of the hall effect pickup.  What I figured was I'd power the speedo from an external source and then send a signal to the white wire going into the meter from the hall effect pickup.  I can do that part, but if that's ~5v+  I wasn't sure what to do for the ground, so from what I'm reading, I just tie that back into the ground lead of the sensor wires.

Trip
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Yep, all grounds have to be connected, gadget, sensor and Arduino. As to the wire colours that's up to you to figure out but if the wire going to the sensors isn't

red +
white signal
black GND

I'll eat my oscilloscope.

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Rob
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Put down the knife and fork smiley that's what the colors are, I'm just trying to figure out how to bring the Arduino into it, whether I need to do something with the red+ coming out of the gauge, or ignore it since I'm powering the white directly.  Last night, I powered up the gauge, wired the black and white wires to the arduino and punched in a frequency.  The odometer started rolling, so I know it was working, looks like the next step is to figure out the frequency/speed correlation.  For some reason, the speedo hits 20 when I power it up (it is possible the needle isn't zeroed) but I can only get it to respond to a certain range 15-30mph, regardless of the frequency. 

I think I'm going to rewrite it to sweep from 0Hz up through nHz and see if the needle sweeps, I've just been using a fixed value till now.
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Sounds like you're well on the way to getting it sussed. You shouldn't need to use the red wire.

The sweep is a good way to go, if you know what the HE sensor measures you should be able to calculate the max frequency.

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Rob
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Thanks for the info!

I was thinking on it while in a meeting this morning (yeah, it was that interesting of a meeting) and I think the other part I need, in addition to sweeping it, is to add in another piece of code to display the frequency.  Searching now for a pot controlled tone and frequency counter that I can put together.  This will help with both the speedo as well as the tach calibration.
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