I'm want to interface to a circuit which grounds the input. What it expects is the arduino to hold the line at 5V, and then it has a transistor or similar to ground that 5V signal to give a percentage of speed. It's drawn as attached - the transistor at the top (ECU) takes the 5V held high signal …

Interfacing to circuit which grounds the input

tocpcs January 22, 2013, 5:51am 12

What size pull up resistor ? I'm thinking 1k.. (just enough to hold it high so the ECU gnds it)

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