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Not me, but Mr. Ohm Can Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Sun, 13 Sep 2009 16:27:17 In Reply to: Your PC can record both sides at the same time!, Marvin Stockman, Fri, 11 Sep 2009 15:56:51 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The voltage on each coil will be around 13.5 volts or ground. To knock this down to around 1 volt, you just need two resistors (per leg), one about 12.5 times the other. But this doesn't need to be really accurate - you'll see higher than 12 volts (more like 13.5), and the line-in can take some overvoltage. Put the two resistors in series, the larger value (call it A) tied to the coil, the smaller (call it B) on the ground side. Take the point where the two resistors join to the PC.
So what values to use? 1 ohm or 1 million ohms? I'd recommend a 10K ohm resistor on the low end, and 120K on the high end. The input impedance of the PC is very high, which means you can use large resistors. And you don't want to put a load on the ECU.
The equation is simple - a voltage divider attenuates the signal by the ratio of B/(A+B) - using the setup mentioned above.
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