dirty RPM data

chumpy36
Posts: 36
Joined: Sun Dec 11, 2005 2:26 am

dirty RPM data

Postby chumpy36 » Wed Apr 05, 2006 11:25 pm

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

DaMan
Posts: 7
Joined: Fri Apr 07, 2006 7:51 pm

Postby DaMan » Fri Apr 07, 2006 7:56 pm

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.
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VW GTI w/DL-1

chumpy36
Posts: 36
Joined: Sun Dec 11, 2005 2:26 am

Postby chumpy36 » Fri Apr 07, 2006 8:55 pm

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

DaMan
Posts: 7
Joined: Fri Apr 07, 2006 7:51 pm

Postby DaMan » Sun Apr 09, 2006 4:17 pm

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?
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VW GTI w/DL-1

chumpy36
Posts: 36
Joined: Sun Dec 11, 2005 2:26 am

Postby chumpy36 » Mon Apr 10, 2006 12:40 pm

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

Steve Wynveen
Posts: 26
Joined: Sun Dec 11, 2005 4:56 pm

Postby Steve Wynveen » Mon Apr 10, 2006 8:34 pm

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

RTUSA
Site Admin
Posts: 457
Joined: Fri Feb 24, 2006 7:34 pm
Location: Richmond, VA, USA

Postby RTUSA » Mon Apr 17, 2006 1:14 am

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


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