| 摘要 |
A circuit includes a plurality of inexpensive resistors connected at one end to the open collector outputs of an output array of NPN output transistors which are connected to a wiring harness or the like for selectively powering a preselected load. The opposite ends of the resistors are connected to the base of an NPN sense transistor. The output NPN transistors, when in the on condition, are biased well into saturation for normal loads and therefore provide a very low Vce (sat) when properly connected through the harness to the intended load. In the off condition, the output NPN transistors look essentially like an open circuit. Vce (sat) is lower than the base turn-on voltage of the NPN sense transistor which has a grounded emitter. The collector of the NPN sense transistor is connected to a source of voltage through a pull-up resistor and to an input of the microprocessor which controls the signals to the output array transistors. The base of each output transistor is connected to an LED to provide a visual indication of which inputs are on and to help the technician locate an area on the circuit board or wiring harness corresponding to a particular function or load on the vehicle.
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