What's the left side that you already have? It seems to me like the right general strategy is to put a resistor between the ground track and ground (instead of having them connected directly), and do a thresholded voltage measurement across that resistor. If you can get an appropriate mosfet (so that its min V_GS * the range of currents you want to supply isn't too big a fraction of 12 V), it should work with a pullup resistor to produce your desired signal for a high-impedence input (so not an LED directly, but logic driving one). Or measure it with an analog comparator; ICs are cheap these days.
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Date: 2006-12-15 06:53 am (UTC)