Mobile controllers receive information from many devices installed throughout a machine.
Some signals are simple ON/OFF states, while others represent continuously changing values such as pressure, temperature, or position.
These signals are commonly connected to two types of controller inputs:
Digital inputs
Analog inputs
Understanding the difference is important when selecting sensors, configuring controller I/O, and designing machine control logic.
This article explains how analog and digital inputs work in mobile controllers and where each type is commonly used.
A digital input represents a discrete state, typically interpreted by the controller as:
ON / OFF
HIGH / LOW
1 / 0
For example, a limit switch may tell the controller whether a mechanical component has reached a specific position.
Limit Switch
↓
Digital Input
↓
Mobile Controller
↓
ON / OFF
Typical devices connected to digital inputs include:
Push buttons
Limit switches
Proximity switches
Pressure switches
Relay contacts
Seat switches
Door or cover switches
The controller does not need to know a continuously changing measurement. It only needs to determine the current state.
Consider a boom equipped with a limit switch.
When the boom reaches a defined position:
Boom Reaches Limit
↓
Limit Switch ON
↓
Digital Input
↓
Mobile Controller
↓
Stop / Limit Movement
The controller can use this state as part of its application logic.
Another example is a parking brake switch:
Parking Brake Applied → Input ON
Parking Brake Released → Input OFF
The control program can then determine which machine functions should be available in each state.
An analog input measures a signal that varies across a range rather than simply switching between two states.
Common analog signals include:
0–5 V
0–10 V
4–20 mA
Resistive sensor signals
These signals can represent physical measurements such as:
Hydraulic pressure
Temperature
Position
Fluid level
Joystick position
For example:
Pressure Sensor
↓
0–10 V
↓
Analog Input
↓
Mobile Controller
↓
Pressure Value
The controller converts the electrical signal into a value that can be used by the machine control software.
Suppose a hydraulic pressure sensor has a measurement range of:
0–250 bar
and an output range of:
0–10 V
The relationship may be:
0 V → 0 bar
5 V → 125 bar
10 V → 250 bar
If the controller reads 6 V, the corresponding pressure is approximately:
150 bar
This conversion is known as sensor signal scaling.
After scaling, the controller can use the pressure value for control, alarms, diagnostics, or HMI visualization.
The basic difference is the type of information they represent.
| Feature | Digital Input | Analog Input |
|---|---|---|
| Signal type | Discrete | Variable |
| Typical information | ON/OFF | Measurement |
| Example | Limit switch | Pressure sensor |
| Common signals | HIGH/LOW | 0–5 V, 0–10 V, 4–20 mA |
| Typical use | Status detection | Measurement and control |
| Scaling required | Usually no | Usually yes |
A simple way to understand the difference is:
Digital input = What state is it in?
Analog input = How much is there?
Most mobile machines require both analog and digital inputs.
For example:
Limit Switch ── Digital Input ──┐
│
Seat Switch ─── Digital Input ──┤
│
Pressure Sensor ─ Analog Input ─┤
│
Position Sensor ─ Analog Input ─┤
↓
Mobile Controller
↓
Control Logic
↙ ↘
Outputs CAN / HMI
The controller combines information from different input types to determine how the machine should operate.
For example, a hydraulic function might only be enabled when:
The operator is seated
A safety-related machine condition is satisfied
Hydraulic pressure is within the expected operating range
The requested operating mode is active
Each input provides a different piece of information to the control logic.
Real-world electrical signals are not always perfectly stable.
A mechanical switch can briefly change state several times when pressed. This is known as contact bounce.
Without filtering, the controller might interpret one button press as several rapid state changes.
Software debounce can help produce a stable digital state:
Raw Switch Signal
↓
Debounce
↓
Stable ON / OFF
Analog signals may also contain electrical noise or small fluctuations.
Filtering can help stabilize sensor measurements before they are used by the control logic.
However, excessive filtering can slow the response of the signal, so filtering should be selected according to the application.
Input processing can also include diagnostics.
For an analog sensor, the controller may check whether the electrical signal remains within an expected range.
For example, with a 4–20 mA sensor:
Expected Signal
4–20 mA
↓
Valid Data
Abnormal Signal
↓
Possible Sensor /
Wiring Problem
Possible causes can include:
Broken wiring
Loose connectors
Sensor failure
Incorrect supply voltage
Short circuits
Digital inputs can also be checked as part of the machine logic, especially when multiple signals should agree with each other.
The exact diagnostic capability depends on the controller hardware, input circuit, and application software.
Reading an input is only the beginning.
The controller uses input information to make decisions and control outputs.
For example:
Joystick
Pressure Sensor
Limit Switch
↓
Mobile Controller
↓
Control Logic
↓
PWM / Digital Outputs
↓
Hydraulic Valves
At the same time, important input values can be transmitted over CAN to an HMI.
The operator may then see:
Hydraulic pressure
Switch status
Machine position
Warning conditions
Operating mode
This connects physical sensors and switches with the overall electronic control system.
Before connecting a device to a mobile controller, engineers should check the device specifications carefully.
Important questions include:
Is the signal analog or digital?
What voltage or current range does it use?
Does the controller input support that signal?
Does the sensor require an external power supply?
Is signal scaling required?
Is filtering required?
Does the application need fault detection?
For example, a 4–20 mA sensor should not simply be treated as a 0–10 V sensor. The controller input must support or be appropriately configured for the electrical signal being used.
Correct I/O configuration is essential for reliable machine operation.
Analog and digital inputs allow a mobile controller to receive different types of information from the machine.
Digital inputs are commonly used for discrete states such as switches, buttons, and status signals.
Analog inputs are used for continuously changing measurements such as pressure, temperature, position, and level.
In a typical mobile machine:
Sensors & Switches → Controller Inputs → Control Logic → Outputs / CAN / HMI
By selecting the correct input type and properly configuring scaling, filtering, and diagnostics, OEM engineers can build more reliable and easier-to-maintain mobile control systems.
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