Matt Romanowski

First, you have to find out if it's voltage or resistance. Most likely, it's a resistance based sensor. If resistance, you'll have to put in a pull up resistor with the wire connecting it to the dash. Before doing that, you'll have to measure the resistance when it's at alarm condition and not. Once you do that, in RS3, there is a nice new feature for making custom sensors where you can input resistance and pull up resistor size instead of voltage. You'll make a sensor that has a value of 0 for full and 1 for empty. Then, set the alarm to go off at 1 and you'll know when you're low on fluid.

Now, most people teams I work with will put in a pressure sensor in the coolant system so they can make sure the water pump is good and if you have a leak, the pressure will start to drop. I don't know what pressures a cup car runs at, but it will be something just below the cap pressure.

Let me know if this makes sense or you want a more detailed info on how to make the sensor.

Toby Pennycuff

Matt, does Radio Shack typically have these kind of resistors? Or does this mean a trip to Frys?

Is there any documentation from AiM on how to build these sensors and when you would, or would not need resistors, etc???? Trying to build these sensor tables and figure out the wiring componentry seems incredibly difficult.

Toby Pennycuff

BTW, I am NOT whining or b*tching here ^. It's just hard to understand why when one spends as much as you do for a data acquisition unit that the documentation is so scant.

Matt Romanowski

Hi Toby,

Yes, it's just a 2700 ohm resistor, so you can probably get it at Radio Shack or any other electronics place. You need the resistor anytime the sensor reads resistance instead of voltage. For sensors AiM sells, the cables already have this worked in. When you do a custom sensors like you want, you are on your own.

I'm just leaving for Christmas dinner. When I get back tonight I'll give you more details on the how with some examples.

jwasilko

If you're really worried about losing coolant, the better solution is a coolant pressure sensor. If you've lost pressure, you're likely losing coolant.

I've got one on my race car that triggers an alarm on the MXL if I'm under a set PSI.

ProCoach

And on your MXL2...

Matt Romanowski

I just wrote this up so you can see how to make the custom sensors and how to work with them. I also included Roger's document on how to do it in RS2 for anyone who has an MXL or Evo4.

Here's the link http://www.trailbrake.net/featured-a...custom-sensors

Let me know if this helps or makes more questions! We'll get you everything working for you in short order!

Toby Pennycuff

Thanks Matt. Good reference material on how to define and manage custom sensors in RS3 and RS2. The information is much appreciated.

So, I will modify my earlier ask as I now realize that the "mechanics" of defining a sensor are relatively straightforward when documentation is available.

Perhaps the better questions to pose are these:

1. How does one go about determining the proper sensor values when there is little documentation from THAT manufacturer on how the sensor works?
2. For those sensors that report to the DME or ECU, how does one go about tapping into that signal without degrading the original signal to the DME? Can you simply add a new lead into the existing connection at the sensor?
3. How does one, who is NOT an electrical engineer, determine whether resistors or other devices may need to be incorporated into the harness? And how would that be accomplished?
4. Is it fair to always consider using the Pegasus MC-314 cable as a starting point to connect to an existing sensor or feed already in the car?

Not trying to be a pain here, but many of us are trying to use these tools and just need some good sources of data to help us build these capabilities. And few of us have ready access to race engineers or EE's that know this stuff like the back of their hand.

TXE36

This may not be that tough to resolve. I am assuming what you want to tap is the the wiper of the factory pot that feeds a voltage back to the ECU. The key to doing this is the overall resistance of the pot versus the input resistance of the AIM input.

Making numbers up, if the pot is 1K ohm, and the AIM input resistance is also 1K ohm, that's a problem.

However, if the pot is something like 5K ohm, and the AIM input resistance is 100K then that is likely fine.

Ideally, you want the pot resistance to be low, and the AIM input resistance to be high. The ECU probably does allow some slop in the nominal value of the throttle pot resistance, so if you change it by a tiny bit, it likely won't matter.

-Mike

Toby Pennycuff

Thanks for the detail Mike. Understand the principle and will try some measurements out.

kristap

Thanks for the Christmas writeup, Matt! The detail is appreciated and I really like your out-of-the-box idea for the custom driver switch.

Matt Romanowski

Great questions! I would probably preface all of this with: This is the reason AiM has provided certain sensors so that all this work is done for you. With the AiM sensors, you just plug them in, choose the correct sensor for the channel, and then it works. No muss, no fuss.

But, for other applications, here we go. Finding sensor info from manufactures can be very hard. If it's a motorsport sensor, many of those companies will provide a calibration table with the sensor. You can almost always call and get one from them. For OE sensors, sometimes you can spend lots of Google time and find the info. For the really tenacious, you can set up tests to create the info yourself.

I don't normally tap into an existing sensor. In my opinion, you don't want to tap into the factory harness, with potentially crispy wiring in an older car, and take the chance of creating a problem. Also, if you have a running problem, you don't want to be worrying if it's from you tapping into the harness or if it's something else. The expense of the additional sensor is worth it in my opinion.

You only need the resistor for sensors that don't measure voltage. You should always check with the manufacturer or on the spec sheet, but a general rule of thumb is if the sensor only has 2 wires, it needs the pull up resistor. Again, when buying an AiM sensor, this is all done for you.

That cable (available from any AiM dealer) would be a good way to start. From a money perspective, it's almost always cheaper to buy the sensor, with the wiring attached, from an AiM dealer than to do it yourself. There are a good number of sensors that you can buy with the wiring and connector on it cheaper from a dealer than a bare sensor from the manufacturer.

I know you're not trying to be a pita. There is so much to learn about data and integrating it with each specific car, that is can be a bit overwhelming. Folks with newer cars with strong CAN support have it easy. For anyone without all of that, it's much more work, but can still be done.

ProCoach

And I think that's where the collective dealer strength helps a LOT here on RennList. Between Matt, Jerry and I, there have been a LOT of installations on specific cars over the years.

My experience is somewhat different because I started doing this long before CAN and vehicle sensor information could be easily collected from the car, so you HAD to install new or piggyback onto existing sensors. Also, much of my focus is on historic race cars, cars that have no ECU to "need" that existing sensor info, so I don't consider adding sensors to be much more work.

Whereas piggybacking on CAN can definitely cause some niggles with signal quality, especially if there is an "acknowledge receive" signal receipt sent electronically back to the CAN twisted pair (wrong config in the logger in AiM can do this, Video VBOX has a check box that needs to be unchecked, etc.), and no one should EVER piggyback off a CAN based system's sensors for RAW SENSOR VALUES, very rarely have I had an issue connecting to an earlier, "dumber" full range, 0-5v throttle potentiometer on an older pre-CAN car, such as a 951 or 993. I just sent an ECU pinout and color code for testing and verification to a 993 customer that wants to do just that!

Temperature and pressure have been MUCH more of a challenge, and for that reason, I recommend, as Matt does, the AiM sensors for AIM systems. MoTeC has sensors available that are a great deal less expensive than they used to be and very good quality, but generally my rule of thumb is to use the sensors provided by the logger manufacturer. Race-Pak and their V-Net were one of the first to provide plug and play sensor capability, Race-Keeper provides that in a limited way, too.

I have seen situations where folks have entered custom sensor values that were off enough to not allow for a reliable value reading at the display, with very deleterious effects, so this, in my opinion, is not where you want to forage for value...

The documentation is getting better. I learned about pull-down (dropping) and pull-up resistors during dealer training with Chris Brown at MoTeC, but another simple explanation is Traqmate's AEM sensor installation instructions. The major reason I went from TraqDash to AiM was due to so many people wanting to add engine health monitoring to their existing driver performance monitoring, and there was just no good, reliable and accurate way to do that adding sensors (or piggybacking off anything more than a throttle pot) with the TraqDash, even though they tried to make it easy to do that.

Remember, the earlier cars (964, for example) follow the old Jetronic model of a two-position throttle position switch (idle/WOT), and do NOT offer a variable value that loggers can use...

Toby Pennycuff

OK Matt, Jerry and Peter: I'll bite.....

What sensors and inline couplers would you recommend for a 2001 GT3 Cup? I would like to be able to measure and report the following:

1. Oil pressure
2. Oil temperature
3. Water temperature
4. Coolant system pressure (lots of great suggestions from folks to monitor this value - thank you!)
5. Coolant level in expansion tank (a simple OK or low value, like an idiot light)
6. Fuel level (already dealt with via an ICM fuel sensor)
7. Throttle position
8. Crankcase pressure, eventually

Which AiM sensors do you recommend and what couplers/adapters/fittings should be used if I am trying to retain existing feeds (to preserve the car's legacy - yes, I am a NUT about that kind of stuff. This is why I am trying to tap into existing sensor feeds where possible.).

924RACR

Personally, I'd just use a switch for an idiot light for water pressure - and do, on my car, sourced from Longacre direct. After all, it's not something you want to log and analyze after the fact - you need to know about and react to immediately.

Similarly I wouldn't rate fuel level as something that needs to be logged, just checked between sessions.

Rather, replace those with steering angle and brake pressure... much more useful for driver development.