RAVE said:

SLABS raise/lower
Before enabling a SLS vehicle raise/ lower request, the BCU checks the logical condition of the following inputs:
l Ignition state.
l SLABS raise request.
l SLABS lower request.
If the ignition switch is in position 0 or I, the vehicle raise/ lower request is off.
With the ignition switch in position II, and the 'SLABS raise' request and 'SLABS lower' request both off, the vehicle
raise/ lower request output is driven at 25 Hz with a 50% duty cycle and the vehicle height remains unchanged.
If the 'SLABS lower' request input is on, the vehicle raise/lower request output is driven at 25 Hz with a 25% duty cycle,
lowering the vehicle.
If the 'SLABS raise' request input is on, the vehicle raise/lower request output is driven at a 25 Hz with a 75% duty
cycle..

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David Pye said:

Hi Sierrafery - that is just the information I need.

I can easily generate a 25Hz square wave, and use pulse width modulation.

What I think I will do is put a switch on the rear body panel by where I put my trailer socket so I can press up/down when hitching up.

I'll update with what I come up with. It should be able to be done for maybe 10-15 quids worth of parts

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David Pye said:

The three piccys attached show the PIC generating a 25Hz sine wave with 50%, 25% and 75% duty cycles. With a bit of luck, this should make the SLABS ecu send the air suspension up and down. I will have a look and see if the SLABS pin has a 50% cycle 25hz wave on it to begin with, and if so, I will try substituting it for my signal. I will need a small amount of interface circuitry to boost the volts, as my poor little PIC uses 5V, not 12V.

But it's a start!

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//Sketch for land rover discovery 2 SLS controller. (prototype!)
//Author: David Pye davidmpye@gmail.com
//Version: 0.1 13/12/12
//Licence: GNU GPL v3.0

#define SLABS_PIN 13 //pin to connect to the SLABS ecu.
#define PIN_UP 10 // grounding this will send us up
#define PIN_DOWN 11 //grounding this will send us down

#define FREQ_HZ 25

int cycletime = (1/(float)FREQ_HZ) * 1000;


int dutycycle, ontime, offtime;

// the setup routine runs once when you press reset:
void setup() {
// initialize the digital pin as an output.
pinMode(SLABS_PIN, OUTPUT);

pinMode(PIN_UP, INPUT);
pinMode(PIN_DOWN, INPUT);
digitalWrite(PIN_UP, HIGH);
digitalWrite(PIN_DOWN, HIGH);
}

// the loop routine runs over and over again forever:
void loop() {

if (digitalRead(PIN_UP) == LOW) dutycycle = 75;
else if (digitalRead(PIN_DOWN) == LOW) dutycycle = 25;
else dutycycle = 50;

ontime = cycletime * (float)dutycycle/100;
offtime = cycletime - ontime;

digitalWrite(SLABS_PIN, HIGH);
delay(ontime);
digitalWrite(SLABS_PIN, LOW);
delay(offtime);
}

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David Pye said:

PI had some grief last week getting the air susp off the bump stops in the cold after everything had been jacked up (comp duty cycle exceeded...!)
Last thing I need is to break the car here so I can't drive it home to where my tools are ;-)

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