Z22SE water temp reverse engineering (VX220 only?)

[rabidh]

Hi, I think a lot of people are considering new ECUs now, so maybe this would be handy. As I'm swapping mine out, I figured before I did I'd really like to be able to have a working water temp sensor, so I took out my scope and looked at the signal.

It's Pulse-width modulated... the signal goes from 0 to 12v, sitting at 0v normally.
Exactly every 10ms a pulse starts (so frequency doesn't depend on temperature) - but the pulse length does change depending on the temp. I didn't get to measure everything as it rose quite suddenly, but there's more than enough here

Measurements:
indicated temp, pulse length (ms)
70,0.888
72,1.28
75,1.528
76,1.72
77,1.8
79,2.02
80,2.22
82,2.56
84,2.76
86,3.00
89,3.38
90,3.58
91,3.7

So if you're handy with a 555 timer you could probably knock up something close - or I imagine a lot of after-market ECUs will handle PWM outputs like this. Unfortunately I'll be doing it from my ECU rather than making a separate box, but it'd be dead easy to use a PIC and create a proper, accurate temperature meter that worked off the Z22SE water temp sender.

 

[rabidh]

I just used zunzun.com (it looks like a really cool on-line function finder!)

pulse_ms = a + b*temp
a = -8.3102499999999999
b = 0.13174999999999998

 

[vocky]

Alanoo and I were looking into this the other week, the elise S1 does not use pwm but the elise S2 and vx220 do.

I gave up again and fitted an elise S1 temp sender for my revotec temp gauge, a perfect fit in the saab head too

 

[exmantaa]

So for my understanding; this was the ECU's temperature signal going to the Stack display. Right?

 

[vocky]

yes, which is why I couldn't get it to work after fitting a standalone ecu, basically the ecu sends a PWM signal to the stack.

if you fit an Elise S1 stack then you can simply fit an Elise S1 temp sender, but the Elise S2 and vx220 stack dash needs a PWM signal

 

[alanoo]

Many standalone ECU are capable of sending PWM signals vocky

I somewhat regret I didn't spent more time choosing my ECU, if I had to redo this I think I'll go for a Sodemo EV11 or a Solaris

 

[vocky]

my Alpha is locked though

 

[alanoo]

Well, if there's a volunteer to make some of these, I guess there will be at least two buyers

 

[alanoo]

Ok, I need that, just saw on my ECU alerts I reached 111 °C last time on track

Any idea what kind of components will it need and/or basic schematics ?

 

[rabidh]

If you're going to make it yourself you'd probably want something like this:

http://www.microchipdirect.com/products ... s=DV164120

It's the programmer, and has already got the PIC on a PCB, with a little proto area so you could use that board

You'd want :
* a PIC (or the board above). If not, the 8 pin PIC12F675 would do you
* a 5v regulator (L78L05) and capacitor for the 5v (~47uF)
* one transistor/FET and a pull-up resistor for the stack temperature output
* and a resistor (3k6?) and capacitor ( to help protect the analog input, and a resistor (3kish?) to pull the temp sensor up
* an FET to drive the fan (or does the ECU do that?)

and that's it. I can give you the code I have. It's outputting it's temp in degrees C to the stack just fine now.
But... I'm still lacking decent calibration data for the GM temperature sensor. does anyone have it?

 

[rabidh]

Something like this - the diagram is a bit shoddy (for some reason the labels don't come out on vertical stuff).

I guess it might be worth sending it to one of these PCB prototype places and getting a few knocked off, but to be honest they could be wired up by hand quite easily.

The 4 pin just takes 12v, water temp signal, wire to stack, gnd
The 6 pin is the in-circuit programmer, mainly just used for changing the software after the thing is all soldered together.

 

[alanoo]

I'll try to ring the guys at the elec dept at my mates work to see if they can help us with that

the ECU controls the fan of course
I do not have the GM sensor calibration table unfortunately as we use a Bosch Motorsport sensor, supplied with our standalone, so didn't bothered recreating the calibration table of the OE sensor

 

[rik1083]

I'll probably work on this when i get my other stuff sorted.. if you can wait?

 

[rabidh]

If anyone is interested I've got the Cadsoft Eagle CAD files for the above circuit now (so a PCB can be layed out) - although it's not exactly complex in the first place. I have the (paid) home user version, but assuming the totally free version will read the files, it would easily lay a board out.

I have to have something in my car, so will probably work out some rough tables. Because I haven't got the calibration, currently it's reading temp fine, but it's a reading a few degrees high IMO. (Maybe that's no bad thing .

Around 100 degrees C the sensors seem relatively linear, so I'll probably have to have a mini GCSE science experiment, take it out, stick it in some boiling water and measure the resistance it gives at different temperatures. I'd assumed that it would all be standard stuff with tables available, but I've found 3 different resistance tables on the net so far and none of them seems correct

 

[alanoo]

Well I had no progress on this from our guys, too busy on work things.

Has any got some progress with this ?

I really want to get this back, and am even considering buying an AIM dash... winter project maybe... (even if I'll prefer spending on a M32)

 

[rik1083]

I'm still willing to have a go but it's not high up on priority list

 

[rabidh]

Mine's working pretty well, and controlling my fan - although the readout is still a few degrees off because I guessed the curves ... It's part of my ECU code though, and I'm afraid getting it to a more driveable state and life generally is taking all my time too.

But... If anyone knows how to use PICs and the SDCC compiler you're welcome to the code I have. It'd work with pretty much any C compiler with some small changes too.

 

[nickb777]

Need to look to see if the DTA will work and provide a water temp signal

 

[alanoo]

It won't

 

[rik1083]

It won't

:yeahthat: