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Old 03-29-2011, 05:00 PM   #26 (permalink)
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If your DX is stock DPFI your going to need to monitor both injectors. This of course would require using one interrupt per injector rather then the current arrangement of both interrupts to monitor one injector.

My thought on using one interrupt to capture an injector pulse is as follows. A pair of one shots are configured to trigger one on the rising edge and one on the falling edge of the injector pulse. The outputs of the two one shots feed an OR gate producing a signal that has a pulse on both edges of the injector pulse. This signal is feed to an interrupt input. The raw injector pulse is also fed into another digital input. The interrupt service routine is called for each rising and falling edge of the injector pulse and simply needs to check the state of the raw injector signal on the other input to determine what edge called the routine. This approach still requires two inputs to monitor an injector but only one interrupt per injector.

For the input zener diodes I would go with a lower voltage then 5.1 volts. Anything between 4.0 and 4.5 volts would be a better choice. The purpose of the zener is to limit the input voltage below the supply voltage so something less then 5.0 volts should be used. The input logic levels on the MCU are very low with anything over about 1.0 volts being recognized as high. A zener as low as 2.0 volts should work just fine but there is no need to go that low.

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