OK, more detail has been requested, so here goes:
The free "Scope" software actually uses your computer's sound card as a (albeit limited) kind of oscilloscope, the input being the Mic socket of your computer. This means, of course, that the bandwidth of the scope is only from about 20Hz to around 20khz, but for engine diagnostics this is not a problem.
Next step is to make up a cable. I used an old headphone cable, cut off the left and right earpieces and soldered a crocodile clip to each "signal" wire of the Left and Right cables. With the earth screen/braiding part of the L and R parts of this cable, I joined them together and soldered another croc clip (for the earth) making 3 clips in total.
Then I identified the CPS signal wire from the car's wiring loom (I found it easiest to pull back the corrugated wiring conduit right next to the ECU). In my Freelander it was a Light Green wire with a Grey stripe. Then I pushed a dressmakers pin through the insulation so that it made contact with the copper wire inside. I could then connect one croc clip to this pin and the earth croc clip to the metal screen wire which was near the CPS wire (or you could simply connect to battery negative).
Then I plugged this cable into the Mic input of my laptop running "Scope" and after playing about with the Amplitude and Time settings of the program, I got the results shown in my photo above. You can also click on the "Measure" button and it will tell you the frequency of the waveform. So in my example the CPS output is showing the car idling at 62.731Hz (i.e. 62.731 revs per second), which equates to 3763.86 RPM..! Ah, but the Freelander has 4 pickups in the flywheel so you need to divide this figure by 4 giving an idle speed of 940.965 RPM...much more credible!
Hope this all makes sense, but don't hesitate to say if you need more clarification...
Martin
