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Smoothing 5v Output via Rotary Switch

EFI Wiring Fundamentals

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Hey Guys,

I have just finished a refurb of my car and one of the changes I made was to have a rotary switch used to select multiple wastegate duty cycles. I have one of the haltech 12 position rotary switches and have mapped this to an external 0-5v input on my Adaptronic M2000 ECU.

Mark at Adaptronic really helped me out with sorting out the setup using logic inputs on the ECU which would then trigger up to 3 digital inputs based on the 0-5v output from the switch which is set as a number of ranges (i.e 3 to 3.99v). This then allows me to to manage the maximum duty cycle of the wastegate.

Now we have context; I've been doing logging on this to make sure its all setup and working and I've noted that looking at the 12v logging on the ECU and the 5v input they fluctuate in sync with one another. Attached is a screen shot of the log from the ECU where the 12v is mapped to pink and the 0-5v mapped to orange.

My question is; is there a way to smooth out the fluctuations in the 5v signal the ECU is reading? I am looking for a wiring based solution to smooth out the ingress signal to the ECU but maybe it may be better to work with the signal I have?

Attached Files

It sounds like perhaps your 5V supply is derived as a voltage divider from your 12 V supply. The solution is a device called a voltage regulator. The regulator provides a fixed 5V output independent of the supply voltage (there is a spec'ed range).

Now, if your 5V supply is coming from the ECU I would expect it to use a 5V regulator internally. There may be a problem with either your ground wiring, or an internal problem with the Adaptronic.

Lastly, some ECUs have the facility to use a "ratiometric" input. So if the 5V supply has a ratiometric input that is normally 2.5V. Let's say the ECU is measuring 5.2V and the Signal is 2.6V, you would get the same table selection as those the 2.5V signal were present. So you might check if the input/ calibration type can be set to ratiometric.

Hi David,

Thanks very much for taking the time to explain this all to me.

I've just gone through exactly this with my LS alternator as I have a Haltech iC7 dash I dont have a charge light in the dash so wired up a DC-DC 12v-55 step down to the L pin on the alternator. This then allowed the charging circuit to power up and the alternator to provide power.

I actually rigged up the same thing with a 78XX 3 pin VR; and a 480uf cap and for testing that did the job - but it did get warm.

I'll use this to test my setup and will review my wiring as well.

Thanks for helping out a home hack just wanting to learn

You may also wish to investigate using a ZENER diode for the voltage regulation - there are numerous circuits for this on the interweb, depending on the amperage you expect.

I haven't really done any circuit design in the last 25 years, so can't really help any further without a fair bit of revision, sorry.

Hey Gord,

Thanks for the hot tip! I've just ordered a handful of those diodes as I Am going to build a test bench where I can test these things out of the car before introducing them into the ECU and 12 battery.

I've found a number of diagrams so ill follow them as best I can and test this out.

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