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EFI Tuning Fundamentals: Digital Inputs

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Digital Inputs


00:00 - All of the sensors we've discussed so far have been analogue inputs, which means they offer a continuously varying signal.
00:06 ECUs will also accept digital inputs which are a type of input that varies between two voltage states.
00:13 The voltage can either be high or low.
00:16 You can think of it like a simple light switch in your house.
00:19 The light can be on or off, but nothing in between.
00:22 These inputs can be used for two main functions.
00:25 Either they can monitor a switched input such as a clutch switch, or they can monitor a frequency input such as a wheel speed sensor.
00:33 There are a wide range of typical uses for a digital input.
00:37 These might include vehicle speed inputs, turbo speed inputs, driver switches to turn functions such as launch control or traction control on or off in the ECU, or for inputting digital sensors like as a fuel composition or ethanol content sensor.
00:52 Often, the ECU will include an option for what's known as a pull-up resistor on these digital input channels, and it's worth understanding what this is and how it works.
01:02 If we consider a digital input that will switch to ground when it's active, then the ECU needs to be able to detect a change in the voltage state when the switch is in the on compared to when it's off.
01:13 The problem is that when the switch is in the off state, no voltage is applied to the digital input pin on the ECU, so it's not possible for the ECU to detect a change in state.
01:24 Essentially, the voltage on the input pin is the same regardless whether the switch is on or off.
01:30 A pull-up resistor fixes this and it's an internal resistor inside the ECU that connects the digital input pin to a five volt pin in the ECU.
01:39 What this means is that when the switch is in the off position, the pull-up resistor will pull the voltage at the digital input pin up to five volts.
01:48 Hence the term pull-up.
01:50 This means that when the switch is off, the ECU will see five volts, but when the switch is on and connected to ground, it will see ground or zero volts and this allows the ECU to distinguish between the two switched states.
02:04 Whether or not you need to use a pull-up resistor will depend on how the input has been wired.
02:10 If you're switching the input to ground, then you will need to use the pull-up resistor but if you're switching the input to a highee voltage such as 5 volts or12 volts, the pull-up won't be required.
02:20 In summary, an ECU will also accept digital inputs and this means we can measure a wide range of digital signals that can give it binary information, as simple as whether a switch is in an on or off position or information coming from a frequency input like a wheel speed sensor.
02:37 Often with these digital inputs, a pull up resistor is used to bring the voltage up from 0 to 5 volts when the switch input is in the off position allowing the ECU to distinguish between the on and off states.