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Digital Inputs

EFI Tuning Fundamentals

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Hi, so Digital Input always will work on the on and off state, but how this works in the clutch switch, and with the frequency with speed inputs, turbo speed inputs, driver switches to turn functions such as launch control or traction control on or off in the ECU this can be controlled with on/off state but these can be modified with ECU files also? And, when an input is on the on-state receives Voltage right? So when it is on off there´s already a difference of voltage because it changed to zero, and in what case when a circuit the switch is on and connected to ground, it will see ground or zero volts based on experience building wires? Any help is appreciated I don´t know much about these things.

A digital input can often be measured in several ways:

-- state (i.e. On/Off; Hi/Lo, Active/Inactive). This is what would be used for a switch such as your clutch switch.

-- frequency (i.e. hz, rpm). This would be used for inputs that measure speed

-- pulse width (ie. time or duty cycle). This might be used for some sensors indicating a position. It can also be used to provide a speed value if converted to a frequency.

There are many ways to interpret the active or ON state of a digital input. Often active low is used, as the ECU provides a voltage to the signal pin through a pullup resistor, and the switch just needs to be tied to ground to become active. Some ECU's may have a setting allow you to define a threshold voltage and a polarity -- so you can define -- when the voltage is above or below the threshold make the input active. That is often useful if you are just measuring a signal that has to work with another device.

I'm still struggling to get my DIG 1 to change state with my clutch switch. Would also like to understand some basics of how the pullup alters the voltage.

In my case, I've used a volt meter to confirm raw voltage that is being "sent" to my M150 pin A23 for the Digital 1 input. Here are the various states:

Key Off: essentially 0v (will register ~300 mV)

Key On - Clutch NOT depressed: ~12V

Key On - Clutch Depressed ~3V (but if I disconnect the A connector from the ECU it will be ~ 40mV)

Thanks in advance for any help

You need to use a UDig for this, rather than a Dig input, they work in different ways and the voltage being read is not going low enough to meet the 2V trigger threshold that is set for the Dig inputs on the M1.

Thank you… I thought this might be the case. I’m using most of my UDIG inputs, so alternatively I can rewire the OEM clutch switch to receive ground or a 0V from the M150, correct?

You could , if there are no other devices using that clutch switch as it is wired.

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