DIY Automotive Oscilloscope

If all you want to see is injector opening duration a simple dwell meter will do fine.

Yes, I know. The DIY autoscope will be a very useful tool for investigating other engine sensors, and that is the main aim after going through the loops in understanding and using the Gnuplot. I love to have one but I loath to spend hundreds of pounds on an automotive scope for occasional use.

Oh, I have not replied to the point. Most of these sensor outputs are dynamic; a static DVM reading is just not adequate, or too vague.

Not really anything complex.

I started off with a 100K/1K resistive divider, hooked up to the 'mic' input on my laptop, connected to an injector lead.

I then noticed that if I left off the ground connection, things got lots less noisy, so it's basically a 100K resistor in series with the mic input.

I suspect a MP3 player/recorder will work just fine.

An example of a few injections is

Simply recorded with sox -c 1 -b -r 44100 -t ossdsp /dev/dsp0 -t raw file.out

To capture a 44.1Khz sample rate byte wide stream.

This was then processed with hexdump -v -e '1/1 "%1d\n"' $1|\ awk '!o&&($1>200) {o=1;last=start;start=(NR/44100)}o&&($1

Why not just buy any of the dozens of second hand oscilloscopes on Ebay? You don't need anything flash or even that modern. The oscilloscopes I've seen on crypton tuners and the like aren't anything special.

Maybe 8 analog 8 bit inputs (say thottle position, air pressure, air temperature, oxygen sensor, temperature, ...) and 8 timing inputs. (say injectors, wheel revs, ...)

To be plugged into a laptop, to log every important parameter.

Well, now....I've a whole lot of stuff to learn! Thanks, Ian. Your customized scan is even more versatile than the ScanGauge.

OK...This is my coming summer project!

For those who have some difficulty with the link:

Or this one

No they aren't. But you can't log the data with them, if that's what you want to do.

I look at my 40MHz scope and think about using it sometimes, but for one thing it's bloody awkward to balance in an engine bay, and for another it is so annoying having used £100K digital scopes to be aware of all the things it *can't* do.

You can fix the first half of that with a can old fluke/philips portable scope.

Plenty of oscilloscopes with logging facilities. It's not exactly uncommon.

LOL. Been there with alot of other kit.