Race Technology

I appear to be getting some erratic rpm data from my dl1. I have a mazda miata (95) and have the rpm going to the low voltage input. I've tapped into the diag connector on the car and the problem is I do not get smooth curves but lots of small dips and peaks.

Other cars that I've set up with dl1's (miatas as well) all produce smooth rpm data. I have to smooth mine out for about 1.5 secs before it is even usable.

Any ideas as to what could be causing this?

Interference?

Thanks
Jason

By a dirty signal do you mean your RPM values are jumping? (3000-3250 vs 3000-3002-3-4-5)

A couple of options, one is that you need to use the 12v input instead of the 5v and you are overloading the unit. Get a multimeter hookled up and see what it reads.

Another is electronic interferance - try shielding the cables or ensuring you don't have too much bare wire exposed at either end.

I thought the low voltage rpm input took anything between 0 and 12 volts.

I know the signal is 12 volts so maybe that's the problem.

But I suspect I may have interference as well...

What say you tech support?

thanks

Jason

chumpy36 wrote:I thought the low voltage rpm input took anything between 0 and 12 volts.

From the DL1 tech sheet:

7 external inputs, all 12 bit resolution. 3 inputs are 12v full scale, 4 inputs are 5v full scale. All inputs are protected to twice maximum input voltage. 1 internal analogue input connected to the power supply voltage to measure battery voltage.


The RPM in low is a 5v, the High is a 12v. So if you are in the high then that should be okay, I would next to interfearance. What cabling are you running?

Well I looked a bit more through the docs and found this...


Alternately the DL1 can detect RPM from a low level source by connecting to the "RPM [5v]" input. This is suitable for connecting to RPM outputs from an ECU or Tacho signal. This input requires a minimum input of 5v to trigger it but is protected up to the battery voltage (15v).

That makes me think I SHOULD be going to the low input which is what I'm doing and what others are doing with miatas as well. The signal is a 12 volt pulse train.

I suspect the problem is interference because I just used a fairly small unshielded wire. The wire also is tied together with a power wire for another accessory ( I know I know).

I just hadn't thought of it before. I bought a new shielded cable (audio type) with an insulated copper core and a briaded out shield. My plan is to connect the copper core as signal and then ground the shield to the chassis.

Sound good to everyone?

Thanks

Jason

Yes, if you are suffering from noise, the shielded cable should help.

I found futher information on the low level tach input. Look in the help file under hardware/DL1/connections. RPM [5v] channel description is "5-15v Trigger - ECU or Tacho Use."

Steve

Not much to add except - yes, you should use the low voltage RPM input for a switched 12V signal.