spike

There's a product made by a company Dataq that hooks up to a computer and can monitor/log up to 4 voltages.. (http://www.dataq.com/products/startkit/di194rs.htm). I planned on logging the voltage my diy wideband meter will be putting out but also wanted to log and monitor RPMs, Throttle, and be left with one more in the future. Does anyone know what voltage range the RPM signal is, and whether the graph is linear (can be RPMs = some number x voltage).. what that scale factor (some number) would be? I could easily check it against the AFC I have installed. Also what is the scale factor for throttle %? what are the limits and what is 50% throttle voltage? Maybe someone has done this before.. but I figure for 30 bucks shipped this would be a great tool.. Thanks for any help!

spike

ttt .. Someone must know these values! After I finish writing the software I'm going to post up a how-to for anyone interested. $30 bucks for a datalogger! Can't beat it!

EE_Chris

The problem is that the VSS is a pulsed sensor.

spike

What is the VVS sensor? I figured since both RPMs and Throttle position can be read by an AFC I should also be able to tap into that line and monitor it with the laptop.

EE_Chris

Brain fart....sorry bout' that, but RPM is also a pulsed input.

VSS = Vehicle Speed Sensor

spike

Well if I take enough samples per second I can average them out.. How does the AFC display RPMs in realtime? Is the voltage in the 0V-5V range? Any idea about throttle position voltages? Thanks a lot man

keebler65

this is true. you'll need to get a frequency to voltage converter. check http://www.national.com for the part number and a nice spec sheet to find out the details. i used this chip for an experiemental homemade digital tach.

keebler65

this could cary on your setup since it depends on how your throttle cable is adjusted. if you want accuracy, i would recommend hooking up a voltmeter and take off your intake and watch the plate and write down the voltages.

spike

ahhh thanks.. there's no way to take say 10 samples per second and then average the samples to get an average signal? I absolutely need that voltage converter? Thanks man

EE_Chris

Yep, basically thats what it boils down to. And you'll have to buy additional components on top of that to get the chip working....its not 'hard' though.

Here is a LINK to National's Automotive product line.


[Modified by EE_Chris, 11:01 AM 3/4/2003]

keebler65

yeah i probably should have added that you'll need many other parts to compliment the chip. its really not a good thing to try unless you're knowledgable in electronics so that you can troubleshoot it, etc since some values will need calculations/tweaking.

spike

i really shouldn't need a chip though.. i just need to get a voltage to the laptop so i can start logging it then analyze it later .. the problem lies more in changing that pulsed signal to a constant signal.

Joseph Davis

I haven't so much as looked at the product in question yet, but...

You sure it can't handle pulsed DC input? It should be very easy to accept digital (pulsed) input into a serial port. Analog is the variable voltage level, where data is incremental instead of on/off like digital... whoo, that wasn't a very good explaination.

The chip they are talking about for turning pulsed DC (rpm or VSS input) to an analog 0-5 volt signal is an LM2907? LM2917? It's one of those two parts, can't quite remember off the top of the poor overburdened brain. I have a good dozen in the parts bin across the room, too lazy to walk over and look.

FYI, VSS is Vehicle Speed Sensor, and it is pulsed, too... once again, I can't remember if it's two or four pulses per wheel revolution. There is a direct link between my memory and whether or not I've had my morning coffee. Sorry

I'm curious how your el cheapo datalogging setup works out... I think you should post all Q's and findings here to HT, so everyone can learn from your learning process, but if you have any off-forum Q's I've a fair hardware background and am interested.

spike

thanks for the advice.. i will definitely keep eveyrone informed on h-t because eveyrone is more than willing to help with questions I have..

mos

Have you seen this: http://www.labjack.com

Its more expensive, but I believe it can do RPM with no additional hardware.

spike

yeah i did see that but the price is not even close to that of the Dataq.. and in reality there should not be too much extra hardware..

spike

Sorry to bring up an old post.. but how did you use a chip to change the pulsed voltage to a constant voltage?

spike

And maybe someone knows this.. by a pulsed voltage .. is it a sin wave or square wave?