anyone played with boxster gauge cluster? Options

[Dr Evil]

Question, just say you have to rely on the engines EFI and other things talking to each other to get the final 1/4 tank, and those parts are not used on the conversion, would it be feasible to put gauge guts from a different gauge into the pod? As in, use the needle and face of the Boxter pod, but drive the needle with a gauge with a known range and value set.

[skeates]

Question, just say you have to rely on the engines EFI and other things talking to each other to get the final 1/4 tank, and those parts are not used on the conversion, would it be feasible to put gauge guts from a different gauge into the pod? As in, use the needle and face of the Boxter pod, but drive the needle with a gauge with a known range and value set.

That's an interesting idea. Not sure what things look like inside the cluster, but so long as it isn't one big circuit board that would be a good way around the problem. This weekend I should have some more time to work on this and take a gander inside. I was also wondering if there was a way to separate the pod housing the indicator lights from the rest of the cluster since that would allow this thing to be used with the stock dash.

[timothy_nd28]

It would be difficult to defeat the ECU communication for the 1/4-0 tank status. The gas gauge should be a standard air core motor. By opening up the gauge cluster, it would easy to sever the tracks on the circuit board to the air core motor, then wire up the aircore wire directly, like a 1967 Camaro. What do you think?

[CptTripps]

(IMG:style_emoticons/default/agree.gif) with Andy. This looks a TON better than I was expecting.

You gave me a few ideas about mocking up my center console too.

[skeates]

It would be difficult to defeat the ECU communication for the 1/4-0 tank status. The gas gauge should be a standard air core motor. By opening up the gauge cluster, it would easy to sever the tracks on the circuit board to the air core motor, then wire up the aircore wire directly, like a 1967 Camaro. What do you think?

I had some time this afternoon to tear into the gauge cluster and look at it's internals. The first pic shows each piece of the assembly: 1) The lens covers, 2) The air-core motors and gauge lights, and 3) the circuit board driving it all. (Sorry for the blurry pic)



Looking at the connections, it's next to impossible (for me anyways) to try and trace the circuits driving the fuel gauge air-core motor, however; they've made it pretty easy to tap into the circuit through some header pins on the edge of the circuit board. Pics 2 and three show this connection, and I've already traced out which pins go to the two coils on the fuel gauge motor. My next question is: what's the best way to generate this signal? From what I understand it takes two PWM signals shifted by 90 degrees? This is my first time playing with air-core motors.

[Dr Evil]

Oooooo (IMG:style_emoticons/default/smile.gif)

I like the splicing into the OE motor method mentioned. (IMG:style_emoticons/default/smile.gif) I hope it works.

[timothy_nd28]

To see how this air core motor is wired internally, we need resistances from each leg to each other leg, a total of 12 numbers, tabulated and identified to which connections are being measured (should be 4 terminals).

[skeates]

To see how this air core motor is wired internally, we need resistances from each leg to each other leg, a total of 12 numbers, tabulated and identified to which connections are being measured (should be 4 terminals).

Here are the measurements you spoke of (See pic below for pin ID). Looks to me like the coils are:

Coil 1: Pin1 to Pin3
Coil 2: Pin2 to Pin4

Is there any way to figure out which is the Sin coil and which is the Cos?

[worn]

It would be difficult to defeat the ECU communication for the 1/4-0 tank status. The gas gauge should be a standard air core motor. By opening up the gauge cluster, it would easy to sever the tracks on the circuit board to the air core motor, then wire up the aircore wire directly, like a 1967 Camaro. What do you think?
Looking at the connections, it's next to impossible (for me anyways) to try and trace the circuits driving the fuel gauge air-core motor, however; they've made it pretty easy to tap into the circuit through some header pins on the edge of the circuit board. Pics 2 and three show this connection, and I've already traced out which pins go to the two coils on the fuel gauge motor. My next question is: what's the best way to generate this signal? From what I understand it takes two PWM signals shifted by 90 degrees? This is my first time p

I don't think we are in Kansas anymore. Ohm isn't gonna help me with this one, is he? (IMG:style_emoticons/default/popcorn[1].gif)

[timothy_nd28]

Ok. If you reset the board and have the fuel gauge reading full, measure the voltage across 1 (red lead) and 3 (black lead) and then across 2 (red lead) and 4 (black Lead). Then set the fuel level to half full and repeat the measurements. This will tell us max voltage on the coils, which one is sine and which is cosine, and the polarity of the terminals. We then will have all the information required to make the modification.

[904svo]

From the reading you have a stepper motor gas gauge, you could try to set your
pot to give a full reading on one set of the windings and another pot with reversed
battery and ground to give a empty reading ( gas gauge sender ).

[skeates]

Just finished taking some voltage readings on the terminals. Looks like they each oscillate between negative 5 volts and positive 5 volts, but at a very slow rate (probably takes about a full minute to go through a cycle. Seems like I might need an oscilloscope to figure out what this signal is looking like.

[timothy_nd28]

Is the needle fixed at full level but the voltages are still changing from -5 to +5 volts?
The voltages should be stable when the needle stops moving.

[skeates]

Is the needle fixed at full level but the voltages are still changing from -5 to +5 volts?
The voltages should be stable when the needle stops moving.

It's hard to say whether or not the needle was indeed in it's full position since I cannot take the measurements while it is hooked up to the motor (The components get in the way of a measurement since two of the pins are buried on the bottom). I did give it a good chunk of time though to see if it would stabilize. That said - given my (limited) understanding of air-core motors, wouldn't we expect for the voltage to vary? I was under the impression that they expected inputs in the form of current oscillating in sin/cos wave fashion?

Looks like I'm going to have to pick up some parts to build a motor driver tomorrow

[Dr Evil]

While I dig the scholastic effort in figuring out the step frequency and such, I must wonder if the modification of a stock 914 fuel gauge into the panel would not be loads simpler as you can then use the stock sender, and tank, and..... However, I in no way wish to dissuade you from the path you have chosen as it is very interesting (IMG:style_emoticons/default/smile.gif)

Is the sweep angle the same or similar between the 914 and boxter units?

[timothy_nd28]

No, the voltages do not oscillate as in a motor, but rather each coil generates a magnetic field, and being at 90 degrees of each other, generate a magnetic field at an angle of atan(I coil1/I coil2). So you can achieve deflection of +/-45 degrees with a current level from 0 to max in coil1 (simultaneously changing current in coil2 from max to 0). There is a bar magnet on the needle which aligns with this field, causing the needle to move.

Try to solder wires on the motor pins and re-assemble to run the test and take measurements.

[Dr Evil]

Fascinating. I have never heard of aircore gauges. More explanation here:
http://en.wikipedia.org/wiki/Air_core_gauge

Pretty cool. I am used to the old school type of single coil.

[timothy_nd28]

In my signature, i did a write up on how to do a tach conversion with a air core motor.

[Dr Evil]

Looked at it, bumped it (IMG:style_emoticons/default/smile.gif) Good stuff.

Would the stock gas tank sender be able to be made to work with the aircore? Would an interface be needed that would change the signal from the sensor into a signal that they aircore could use?

[timothy_nd28]

Absolutely using the original sender, everything will be plug and play after the modification