Cal switch scramble button

[Sam Pickering]

So … I have a s6+ pnp in my newage Impreza, I currently run and use the Syvecs rotary calibration switch, utilising 6 switch positions at present, for various table swaps etc.
What I’m wanting to do is to add a scramble button on the steering wheel to jump straight to a preset calibration, eg. Current cal (on rotary switch) to cal 6 for full boost.
Now I have used all of my inputs in the ecu so the only things I can see that are spare so to speak to add a cal switch override input are the rear lambda input that’s currently unused an12 I believe and also the a/c switch request an11 I believe. I tried to cut and wire into the a/c switch request using pin 6 on connector b134 of the Impreza loom into the ecu, now I can get this to work perfectly using a 12v input through a momentary switch but when I program the ecu, because the a/c switch in the pin assignments isn’t assigned to the an11, it becomes out of sync. Is there a solution here or something I’m missing that’s really obvious, or perhaps another way around this utilising a resistor stack inline through a momentary switch to match the resistance cal 6 has on the rotary switch to do the same job whilst not requiring the use of an input so to speak?
For reference, I run the rotary cal switch through a two wire setup using the pull up in the ecu on the 5v reference feed.
Many Thanks in advance

[stevieturbo]

Whilst I've never tried.....

For those who want I presume a momentary Cal change ? ie only when a button is pressed ?

Why not just add a button from 5v to the Cal input ( or ground, whichever is needed ), which would effectively change the switch to the maximum Cal position, as opposed to an "override" position ?
With Cal voltages suitable set of course.

Mechanical it is physically limited to 6 positions, and your additional momentary button can be no 7 ?

No need for any additional inputs to be used.

[Sam Pickering]

That is a very good idea, I’d not thought of that Thankyou very much, I shall do this, I’ll update on here when all is working successfully

[TimH]

If it is a standard 8way Syvecs CAL switch it uses diodes to provide 0.65V(ish) steps, and relies on the 3k pullup internal to the ECU to bias the diodes and get the voltage steps.

If you short the ECU input to 5V it will indeed go to CAL8...but you will put 5V directly across the series diodes between the current CAL selection and ground and most likely burn the diodes out.

I'm sure there are tried and tested ways of doing the override like this (I believe it is one of the reasons for using a diode-chain CAL switch) but off the top of my head I think you could go for a CAL "underride" by switching to ground so it it will actually go to CAL1 when you press the switch. That way you won't damage anything.

Or you could wire the switch in series with the CAL switch "output" and the ECU input and use a normally closed switch - when you press the switch the connection to the CAL switch is broken and it will jump to CAL8.

I think there's another variant of this but I can't recall it or quickly work it out...but don't just wire 5V to the ECU input via a switch with a diode-based CAL switch.

[stevieturbo]

If diodes are a risk, don't many rotary switches use resistors ?

And it will go to whatever cal you set 5v to be. Or even a slightly pulled down voltage if 5v is too high.

[TimH]

resistive CAL switches will be OK; the standard Syvecs 8 way was always a diode type unless they changed it which I think unlikely. 12 way switches are generally resistive types

[Sam Pickering]

Thankyou for the responses, much appreciated, I thought I’d update you with what I did, I went with the momentary switch grounding the signal wire to the ecu, this did exactly what I wanted and I’ve altered the calibration in cal 1 to suit. I’ve added some screen shots below, apologies for the poor quality but I think you can make out the cal switch voltage and cal on screen.
Thanks again guys