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Choose the right resistor as a pull up

Practical Motorsport Wiring - Club Level

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Hi all,

I need a recommendation for choosing the right resistor for my need of a pull up.

Here is my scenario:

GM E38 ECU, pin 48 is the tach signal output. I found out that if I want to use it with an aftermarket tach I will need a 1k ohm pull up resistor spliced in.

My tach is a Racepak IQ3 dash display. The manual says "Connect this input to the tach output signal from your ignition box. The tachometer input requires a standard 5 – 20 volt, 50% duty cycled square wave signal to work properly."

Question 1: Do I really need a pull up resistor? (I'n not really sure)

Question 2: How do I choose the right resistor? I found so much 1k ohm resistors at digikey, for example. How many Watts should I choose?

Thank you very much for any suggestion

Björn

Hello Björn,

The documentation does not mention adding a pull up resistor so it likely already has one on the channel. Connect it up and if you have engine RPM showing, it's all good and you won't need one. If you connect it and don't have an engine RPM signal then you will probably need one. If so, part no- LR0204F1K0 will work.

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