Odd automotive gauge

[wootin24]

Hi guys, i'm attempting to wire up an automotive gauge to my arduino, but am struggling to get it to work. I originally was thinking it should be wired and used just like a stepper, as it has two winding's and four wires, but when i do that it just jumps around and doesn't do what i expected. The gauge also has some sort of spring to return to its home position, so i'm not sure if that is of importance. When i applied voltage across one of the winding's, the gauge shot up to its max position, and when i applied it to the other, it shot to about half. Any ideas on how to make it work? It's a gauge cluster from a 1997 jeep wrangler, if that helps.

[David Hess]

Use one of the windings and put a resistor in series to limit the current.  My guess is that it is like a 0 to 1 milliamp movement but maybe it is a little higher.

[nanofrog]

Given your description, it sounds like you're talking about the battery gauge (typical output V should be ~14Vdc, hence it's the center point on the gauge).

Although there's 4 terminals on it, 2 of them go to the voltage regulator (sensor; this type of gauge uses a push-pull, depending on what the output voltage is), while another goes to the ignition (turns the gauge ON), and the last is to ground (connected to both coils inside the gauge). I don't know the exact pin-outs, but you should be able to trace the wiring relatively easy using the continuity setting (I've only worked on a number of older Jeeps; late 40's - 80's, all of which only use a 3 terminal gauge as it's the older non push-pull type).

So if you're having problems with how it's reading when in the vehicle, the likely suspect is the voltage regulator*, not the gauge. Rather common issue with Jeeps given what's available on Jeep centric forums.

* If it has one, as at some point they put the voltage regulator in the ECM & a temp sensor beneath the battery to be sure it's not overheating while being charged.

If yours is built into the ECM, then the simplest thing to try is to clean off the battery cables and terminals to be sure you've a good connection. With top posts, you can wrap the post with copper so you can get it to tighten (I've done this successfully). Otherwise, you'll have to replace the clamp or entire wire, depending on how it connects to the battery.

[DBecker]

It's probably a quadrature gauge motor.  Two coils at 90 degrees to each other drive a single pole rotor.

You'll need to figure out the minimum current needed to reliably drive the pointer.  In theory you compute the current for each coil by doing sin() and cos() of the desired angle.  But due to various physical complications, including the bias from the spring return, you need to have a multi-factor calibration.  It's much simpler to just manually create a coarse table e.g. every 10 degrees and interpolate.

Consider how you'll drive the coils -- they are inductors, with kickback.  Directly connecting Arduino PWM outputs isn't the best choice.