Carpokes Porsche Forum

My name is Scott and I am in the midst of a major rebuild of a 1986 951. Purchased with a removed engine and mostly disassembled interior, I am slowly getting things back together.

Long story short and reported elsewhere, I am converting to a Microsquirt system. I am going to incorporate an Arduino alongside the MS for added functionality. Here is what I am thinking:

1) PWM fan controller for factory fans. The original resistors and wiring are toast. The biggest power draw from what I can gather on the original setup is the startup. This will solve that with a soft start and unlimited variability. Also will benefit from new wiring. Control for the fan control module will come from PWM output of Arduino fed through CANBUS from analog factory temp sensor.

2) Deleting factory AFM setup and going to a MAP sensor setup. Will use the MAP to drive the factory boost gauge through the Arduino as an analog output (input still through CANBUS).

3) I don't want extra gauges in the cabin, so going to pull the WB AFR data in through CANBUS and let Arduino drive a 16x2 LCD display that will mount a little more discreetly somewhere - maybe in the instrument cluster. At first this will be configured to show AFR only, but may add functionality with a roller wheel/push to enter button in the console to allow other functions to display there.

So...I am looking for the best combination of outputs on the Arduino unit for the control of these items. PWM seems pretty straightforward. The 16x2 display I have has power, ground, and inputs for SCL and SDA. Not sure how the output needs to be wired between the Arduino and the factory boost gauge wiring under dash. Also anyone with code that would support this that is willing to share?

Thanks all - looking forward to being a part of Carpokes!

Welcome to Carpokes!

I cannot help with your specific questions but there are lots of 944 folks here who do wonders with their cars so I'm sure they'll be chiming in soon.

Welcome to Carpokes Scott, and all the best with the rebuild!

Hi Scott,
Welcome to Carpokes. I’m sure you’ll be hearing from a lot of the 944 folks.
Larry

Sounds like you just need a standalone ECU.

Welcome to Carpokes, and thanks for tracking us down!! There are a handful of 944 faithful who have ventured into some of this with Arduinos, etc., but not as many as I would have expected by now. Re your 3 points....

1. Controlling the fans is something Microsquirt can do on its own. I'm posting a youtube below of how Michael ODonnell did it. I'm not sure if he has discovered Carpokes yet, but you should get him over here if you can. He has done a lot of this, and would be a great add here. He uses a digital on/off output, rather than trying to control the speed of the fans. Not sure your electronics background/level, so apologies if this is obvious, you trust you know you can drive the fans directly from an Arduino PWS signal. Those outputs don't have the amps needed for the fan and would be fried if you tried. You would need some type of dc fan controller or controller circuitry -- which could indeed be driven by the PWM output. Fun project, but would take a few brain cells to make it all happen. Here's Michael's version:




2) The boost gauge is quirky, but I went through quite a bit to drive it using an ATMEL 328 chip (same as arduino chip, without the rest of the Arduino board). I have to pull out my notes to really help, but at a high level, it is driven by a .5 to 4.5 dc volt signal -- kind of -- you need to take that signal and connect to a 1.9k and 2k resistor (in parallel) with a small capacitor in between. I'll look up the value of the capacitor for you, but the resistors and capacitor just replicate the driver circuit inside the KLR. Due to the impedance of the gauge, you then see, roughly, 0-1 volts driving the gauge if you probe at the gauge input. The gauge output is 'almost' linear (more voltage, more boost) -- which is typically good enough considering the inherent limitations of the gauge -- but you can fine-tune any particular gauge using best-fit function generators online. I'll dig out the scaling formulas I've used. As Audisport says, you can do this (and the fans) without CANBUS, which would necessarily require more hardware, but if you are using it for other things and/or just want to do it for fun, no reason it can't be done....


3. Use the clock display area, and use the buttons to scroll through the available outputs... !

Yes, a dedicated PWM controller would be a better path. This would work stand alone or with an ECU down the road.

https://creativewerksinc.com/product/pwm-controller/

This is made right here where I live.

Thanks all for the quick replies and I really appreciate the insight. I am intrigued by Tom and AudiSport's comments....

I do have a PWM controller from a Mazda6 (seems to be the go-to for these conversions). It will drive two fans - just have to figure out the best spot to mount it. Looks like there is only a signal wire to that from the Arduino PWM out. Running a new power lead from battery to feed the Mazda box. My understanding has always been that the Microsquirt version of the ECU does not have a PWM output at all, which is why I was thinking I needed to convert it to where it did. I know the MegaSquirt versions do. I'll go back and check the wiring from the Micro as well.

So sounds like the Boost gauge will work just fine using a spare output on the Microsquirt then (e.g. LED1) that is set up to be a variable DC Voltage output. That may make that part a bit easier. The resistor/capacitor part is what I was unsure of, but sounds like I will need that regardless of whether the signal comes from Arduino vs. MS.

Clock is a great idea for the 16x2...will have to see if it fits. Dash is out of the car still so that may be great, and then Ardunio can just display clock as well as AFR.

-Scott

Drscottsmith wrote: Fri Feb 17, 2023 12:05 pm Thanks all for the quick replies and I really appreciate the insight. I am intrigued by Tom and AudiSport's comments....

I do have a PWM controller from a Mazda6 (seems to be the go-to for these conversions). It will drive two fans - just have to figure out the best spot to mount it. Looks like there is only a signal wire to that from the Arduino PWM out. Running a new power lead from battery to feed the Mazda box. My understanding has always been that the Microsquirt version of the ECU does not have a PWM output at all, which is why I was thinking I needed to convert it to where it did. I know the MegaSquirt versions do. I'll go back and check the wiring from the Micro as well.

So sounds like the Boost gauge will work just fine using a spare output on the Microsquirt then (e.g. LED1) that is set up to be a variable DC Voltage output. That may make that part a bit easier. The resistor/capacitor part is what I was unsure of, but sounds like I will need that regardless of whether the signal comes from Arduino vs. MS.

Clock is a great idea for the 16x2...will have to see if it fits. Dash is out of the car still so that may be great, and then Ardunio can just display clock as well as AFR.

-Scott

I wouldn't power the fan controller directly to the battery necessarily, as it may have a fairly high parasitic drain on the battery. I assume the Microsquirt won't be able to control it anyway unless the key is on. Best to wire it into a switched power circuit so you are only drawing current when the ignition is on. You can leave the factory over-ride switch if you want the fans to come on after the car is turned off, if/when the radiator is over a certain temp.

I don't know the Microsquirt, at all, but if it has a variable DC voltage output, then that is almost surely a PWM-generated signal, probably with low pass filter to smooth out the pulses, and effectively the same thing for all practical purposes. If you want to generate the boost gauge signal using that output in the Microsquirt, I'd assume you'll need to populate a table that assigns voltage levels (.5 to 4.5 volts) based on MAP sensor inputs (rather than Arduino code). If you start with a linear function (.5= 0 BAR --> 4.5 = 2 BAR absolute), that will get you in the ball park.

If I were doing your clock display, I'd add outside temps. I miss that in my 951....

Outside temps? It's either 1 of 2 things. Comfortable to drive or uncomfortable because the AC is broke