Technical > Wiring & Sensors
BMW tachometer
rob@vems.co.uk:
The bigger the resistor the smaller the pulse that the tacho receives. Start with 10K and lower the value accordingly (two 10K resistors in parallel will give you 5K)
GintsK:
Did simple input signal for IGBT, MOSFET or output signal from stepper chip work without pullup?
BenFenner:
I can ask DanMartin what value he used for his BMW tach. He looked it up somewhere...
antonch:
Rob, your values worked out of the box, didn't have to modify/tune anything. Very odd how you knew them :)
rob@vems.co.uk:
--- Quote from: GintsK on January 05, 2008, 03:39:12 pm ---Did simple input signal for IGBT, MOSFET or output signal from stepper chip work without pullup?
--- End quote ---
No because the IGBT, MOSFETs etc channels only switch to ground, so you need a power feed, and you need the resistor in there or when the thing switches to ground the current will be massive.
The way it works (sorry if people already understand this) is that when the channel is closed the tacho sees ~12v on its trigger line, then when the channel opens the voltage drops to zero, then back up to ~12V when the channel closes again.
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