Hello,
I am pretty much a novice when it comes to video & data... I just finished my first weekend w/a new VBox HD2 system in my new-to-me SPEC 911. I didn't fuss w/the VBox during the weekend, other than to turn it on to gather video & data. I was mostly focused on getting comfortable w/new-to-me everything else...

Reviewing the data once back home, one of the first questions I have is if having throttle position and brake pressure input shown graphically on the video would be helpful and make it just that much easier for me during a quick video review? Also, maybe engine RPM?

What would it take from a hardware standpoint to set that up? My car is an old, air-cooled 911, so no CAN or on-board computer to plug into for throttle or brake info. Would I use a Micro Input Module, a throttle position sensor & brake pressure sensor & some wiring/plumbing to connect it all together? And finally, I’m not clear how/where the Micro Input Module connects to the V-Box… is it the CAN/Serial port? and if yes, where does the OLED display connect then?

Thanks so much,
Tom

 

Tom, a micro input module (I supply the H version, cleans up the ignition signal from the car) and a splitter for the OLED and MICIN01H. Can supply sensors too.

 

Hi Peter,
Check your email for something from me... I'd like to learn what it would take to add this to my system...
Thanks,
Tom

 

There is probably no need to buy a bunch of sensors. I used the Micro Input Module to get this info on my 99 Spec Boxster, which has no usable CAN. I got the throttle signal off of the existing TPS - I tapped into the wire at the ECU. For brake, I tapped into a brake light circuit and created a math channel that combines it with Longitudinal G. Here is the formula. Abs (([brake input] >=6) * [Long G]) * K
The first part of the formula returns a 1 or a 0 to indicate if the brake is being pressed (i.e., brake light voltage above 6v). This avoids getting a reading when you lift from the gas but do not press the brake. The second part then combines with Long G. The Abs function makes sure it is a positive number. The K is a constant to scale the result so that you get 100% at max braking force. You just need to determine your maximum Long G under braking and divide 100 by that number to get the K. It may not be the actual brake pressure, but it is a great approximation.

 

That’s a great way to do it. Just did this on new Mustangs using an aftermarket ABS that took brake pressure off the CAN. I would say you’re aiming for max long g of at least -1.0 g, and preferably more like -1.1 to -1.2 g full scale.

What is the pin out for the 986 TPS?

Let’s see if we can do this easily on the Spec911.

 

That is a super slick way to get brake pressure! I understand your explanation, but will definitely need help w/the math! My car has a pretty stock aircooled 3.2L per class rules, so no throttle position sensor to grab a signal from for throttle position...
Thanks for the help!

I just looked at my data and the max Long G under braking I found was -.73g ... but I'm sure there's more in it! I was not really getting after it during my first laps in the car, just trying to get comfortable.
Peter, is it better if I call or send you another email?
Thanks,
Tom

 

Send me another email at peter*@*peterkrause.net

Take out the asterisks.

 

Marc, the earlier cars like the 3.2 911 only have a throttle wide open switch and throttle closed switch, not a variable throttle position potentiometer like the 986 or even the 951's. Your braking solution is elegant and simple, though. Works well.

 

For those playing along at home, I believe I connected the MicroInput AGND to ECU 34 (Br/Pk, 0v Sensor ground) and the MicroInput Analog Input (any of AN1-AN4) to ECU 44 (Ye/Bk, TV-signal (throttle)). See red highlight in attached diagram. As shown in the diagram, you can actually get the signals from the ECU or the TPS itself. Note, this is for a 99 Boxster. The actual pins/wiring colors is may be different for other cars.

 

Fantastic! Thanks for sharing.

 

I have throttle position (wire potentiometer), RPM and brake pressure (brake pressure sensor) through the micro input module in my '69 911. For the sensors you just need to figure out the scaling. The only challenge for me was the RPM signal which I have now traced to a faulty MSD ignition box.


The math channel simulating brake pressure through long Gs is an elegant solution and you do not need to wire in a brake light switch as you can simply set a threshold value in the formula. Here is the formula:

Brake from Long Gs = abs(gte(abs("G9"),0.4)*G9")

G9 is longitudinal acceleration

 

Nice, Frank! Glad to hear about the rpm remedy.

 

A few years down the road here and I'm still working out a bug or two - trying to get my VBox scene to show brake pressure using the method outlined by Frank 993 C4S & MJP911 above and also the correct gear. Throttle input is working great via a pot. I installed (thank you Peter K.) and RPM is working, although needs scaling as it reads about 1/3rd too high. I have all 3 inputs wired thru a Mirco Input Module (thank you again Peter K.) and recently tested to verify that the brake light pressure switch is sending 12V to the Micro Input Module when the brake pedal is depressed (which it is). When verifying that, I noticed that I hadn't installed a ground wire to the AGND terminal in the Micro Input Module - should there be one there? Wondering if that's maybe the reason why the brake pressure switch isn't triggering the math channel...? Also need to verify that the math channel is set up correctly...

I worked w/ShakeNBake to have him create the scene for me, which other than the brake pressure and RPM scaling, is fantastic. He's been busy and I hate to bug him too much over these final details, so thought I'd do some troubleshooting here to see if I can nail down these last few things. I need to get the RPM scaled correctly before sorting the gear display as I need to do a test run or 2 through the gears to get some data for ShakeNBake.

In the photo below, we're using GND, +5V & AN1 for the throttle pot. input and AN2 for the brake pressure switch input.

Thanks,
Tom

 

Ok, good progress so far.

No need for the GND on the brake switch input.

Something with the math is the issue.

I don’t use the math anymore for quick analysis, I just make a bar graph that starts at -0.3 and is full deflection at the highest sustained decel I can measure, start with -1.1 long g and tweak from there.

The RPM multiplier should be /2 for four-cylinder, /3 for six-cylinde, /4 for V-8

 

For brake apply data in an old/analog car... here's another approach I've been using in my prototype.

To go beyond mere brake switch and decel data, without the pain (and cost!) of installing a true pressure transducer to measure line pressure, I chose to measure brake pedal travel instead.

But adding a string pot is a pain. Instead, I went for a non-contact IR distance sensor:
https://www.robotshop.com/en/sharp-g...ge-sensor.html

...plus the cable:
https://www.robotshop.com/en/cable-s...ge-sensor.html

For a grand total of $12. Just stick the sensor to the firewall with good double-sided tape, feed it 5V and ground, and it spits out a nice signal 0-5V based on your actual brake application, by bouncing an IR beam off the back of the pedal/your foot. It's accurate enough to, in my experience, show the difference between warm and cold pads/different lining choices in my prototype (which, admittedly, has no booster, so much more direct pedal).

Just an alternate thought for some higher-quality data vs, recombining what you already have...

We're also using them for live, active ride height measurements... joys of aero cars...