Editing Stack (section)

=== Communication with aftermarket ECUs ===
In the Rover engined S2 Elises, the following information is sent to the Stack by the ECU:

* Water temperature - Lotus ECU pin 72, Stack connector pin A6
* Speed - Lotus ECU pin 74, Stack connector pin A5
* RPM - Lotus ECU pin 55, Stack connector pin A4
* Check engine light status - Lotus ECU pin 69, Stack connector pin B5

Water temperature must be configured as a 5v PWM signal at 100hz, with 100% duty cycle at all coolant temperatures below 72c. The dash will not output temperatures below this, 100% duty cycle will cause the screen to be blank which is the intended output. At 72c, duty cycle should be 90%, and then 10% less every 7c over this. E.g. 80% at 79c, 70% at 86c, etc...

Speed is a 5v square wave, the VR sensor on the rear left wheel has 29 teeth, different ECUs may use different methods of calculating speed but the easiest way is usually to drive and compare against a GPS speedo, then adjust the ECU output until the dial reads correctly. 

RPM is a 5v square wave and shouldn't need any messing with.

Check engine light is triggered when the pin is pulled to ground.

There is a pin for the shift light also, but this will also be triggered by the Stack unit internally so isn't usable unless you wanted to use the light for another purpose.