Race Technology

I'm looking at adding the following sensors:

Steering angle
brake pressure
throttle %
oil pressure
water temp (maybe pressure)
4 x shock pots
AFR
Fuel level (stock gauge takes forever to react to adding fuel)
RPM (already hooked up)

Most (probably all, haven't finished spec'ing everything) sensors have the option of +5V input with .5 - 4.5V ratiometric output or 10-30V input and they have a voltage regulator to output a linear 1-5V.

Given the Mk3 has two 500 mA +5V outputs any advice on which way to go would be better? Any issues just running from the car's power? Any reason/advantage to run from the DL1?

Thanks in advance!

I would suggest using the DL1s outputs for sure, they are protected and monitored and nice and stable. The problem with running of the cars main supply is that is goes up and down with engine speed as the alternator charges etc, and it's covered in noise which makes all the sensors look noisy. The only thing to watch is that you don't too much current from the DL1.

Shock pots, steering angle, throttle, oil pres, water temp all only need a few mA each. The AFR runs of car power, so that's not relevant.

The only one to think about is fuel level, these are very low resistance so can take a bit more current, but with 500mA to play with you'll be fine.

The other thing to consider is partitioning the +5v so if you get a short it and hence lose one 5v supply, it doesn't kill all the mission critical signals.

Of those water temp and oil pressure are very important - you might consider putting those on the 2nd reference output by themselves?

Regards,

Support

Thanks for the quick response!

Support wrote:The problem with running of the cars main supply is that is goes up and down with engine speed as the alternator charges etc, and it's covered in noise which makes all the sensors look noisy.

I'd hope the voltage regulators in the sensors would take care of that.

Shock pots

Unless I'm not reading the specs right, the Penny+Giles MLS130's say they draw 3A each?

The only one to think about is fuel level, these are very low resistance so can take a bit more current, but with 500mA to play with you'll be fine.

I have a sensor that takes the resistance and converts it to 1-5V out with a 12V ref signal.

Of those water temp and oil pressure are very important - you might consider putting those on the 2nd reference output by themselves?

Sounds like sound advice. I also have separate gauges that are already in the car.

So it looks like some of my sensors are going to have to run off the car's electrical system. I ordered an MSI pressure sensor for brakes that I'll run from the DL-1.

no - those linear sensors are a few 1000's of ohms each - so they will just be a few mA

Get the spec sheets on the sensors you will use, then add up the current draw. Make sure it's less than the DL1mk3 can provide. Done.

Yes linear voltage regulators work. I use them for a Mk2 - but the current draw on the Mk2 is considerably less than the Mk3.

If you have an resistance based fuel level sensor, then it would get you better resolution to use a ~10VDC (need to check the voltage dropout curves) linear regulator to get a higher, but still stable, voltage supply for the pull up network.

osborni wrote:Get the spec sheets on the sensors you will use, then add up the current draw. Make sure it's less than the DL1mk3 can provide. Done.

Sure assuming you can find and trust the spec sheets. They said they use 3W of power, but looking again it also said 6K ohms, so I'll assume the latter is correct and that'd be ~23 mA (running from the car, less from the DL-1.)

The fuel sensor I'm using dampens the signal, but is sourced from the stock sender in the tank. Don't want to get a low fuel warning every time you enter a corner.

Thanks for the help.

Low fuel warning? You are using a Dash(x) as well?

Most digital volt meters have low amp measurement capabilities.

osborni wrote:Low fuel warning? You are using a Dash(x) as well?

Yes, I have a Dash4Pro. (Actually I have a bunch of RT stuff from over the years, but the car in question is D4Pro.)

I'm running in Spec Miata and will mostly use it to measure the fuel since we run just enough fuel and use ballast to make minimum weight. The stock gauge takes forever to register how much fuel you've added, and I'm too busy (read lazy ) to pump it all out and add it back in between sessions.

That would suggest that you need to find the right balance of signal averaging and smoothing. Enough to take care of tank slop, but not so much that it takes forever to get to the right level.

osborni wrote:That would suggest that you need to find the right balance of signal averaging and smoothing. Enough to take care of tank slop, but not so much that it takes forever to get to the right level.

Yep I luckily work with a EE who made a device for me that takes care of all of it. I just sent him the ohms from the stock sender and various fuel levels and he did the rest.