Digital Inputs problem

[Turbocab]

I have a M400 installed on my Porsche. I recently installed a Bosch 3 wires IAC valve and started the Tuning process. I noticed that the IAC output jumped to a high value, unexpectedly, without any reason, raising the RPMs in the process. After some troubleshooting I found that the Digital Input # 1, assigned to AC Request was activated even with the air condition off. I disconnected the cable and the input continues to be activated. I measured 4.95 V coming out of the Digital input (from the M400), without any cable connected to it, which I think is not good. I connected the cable to Dig input # 2 with exactly the same results. I also reprogramed the inputs as Power steering to no avail. I have the M400 running in my car for about 2 years without any problems. Now is the first time that I used any of the digital inputs. May be there was a malfunction of the Dig inputs from the factory and I didn’t noticed before. Any suggestions?

[Blu302]

Have you got a manual? Check the input characteristics. Digital inputs have a 4700 ohm pullup resistor to 5v. You need to ground it for A/C request. The other way is to use an Analogue voltage input, then you can supply Batt+ for A/C request.

[Turbocab]

Is this the correct wiring for the Pull Up resistor?

Dig In_Pull Up.jpg (44.92 KiB) Viewed 18827 times

[IDP]

Pullup resistor goes to 5V not Ground.

Your switch then goes to ground not 12V

[Turbocab]

Does anyone be kindly enough to show me a drawing on how to connect my AC request signal to a Digital Input? The signal is 12v coming from the compressor clutch coil. That’s the way it is wired from the factory on the car. For me it’s unthinkable that I will need to install an extra relay to trigger the Dig input to ground in order to make this work.

[SprinterTRD]

Just hook up the Clutch wire to the digital input and set "logic polarity" in the parameters setup to 1

This works because the clutch coil keeps the digital input grounded untill 12V is switched to the coil.

You should probably fit a diode between the digital input and +12V to protect the digital input from back EMF when the clutch is turned off.

[Scott@FP]

A/C request comes from the A/C controls and/or ECU, not the clutch. Clutch coil probably pulls too much current to hook directly to an ECU output, there should be a relay in between.

What car is this?

[MarkMc]

Just to clarify.

All Digital inputs on the ECU have a 5v pull-up internally. So, with nothing connected to a digital input you can use a multi-meter to see there is 5v (4.98v is close enough) on all the digital input pins, this is normal. You will also see the same 5v pull-up voltage on the Analogue Temperature inputs.

The digital inputs work by using a simple switch to connect the Dig to 0v. The input logic needs the signal to switch from above 3v to below 2v so 5v (with the pull up) switching to 0v obviously meets this logic and the Input goes active.

You cannot switch 12v into a digital input becasue 5v switching up to 12v does not meet the above mentioned 3v - 2v logic.

If you have something that switches (on/off switches, not analogue signals)to 12v you need to connect it to an Analogue Temperature input set up to be a switched input. With a switched (AT) input you can reset the normal 3v - 2v logic to whatever you want. For example an EVO A/C button switches to 12v, we would connect this to an AT input which sits at 5v and we would set the logic to 5.5v - 6v. When you press the A/C button the voltage goes from 5 to 12 meeting the 5.5v-6v logic and the input becomes active.