Large mobile machines often require dozens of sensors, switches, valves, actuators, and other electrical devices.
Construction equipment, agricultural machinery, mining vehicles, cranes, and other complex machines may need to monitor and control signals distributed across different parts of the equipment.
As machine functions increase, the available I/O channels on the main controller may no longer be sufficient.
Replacing the main controller with a larger unit is not always necessary. Instead, OEM manufacturers can use remote I/O modules to expand the control system through CAN Bus.
This article explains how I/O expansion works in large mobile machinery, where remote I/O modules can be installed, and how distributed I/O architectures help create more flexible and scalable control systems.
A mobile machinery controller communicates with many field devices through input and output channels.
Typical inputs include:
Pressure sensors
Temperature sensors
Position sensors
Limit switches
Joysticks
Proximity sensors
Typical outputs include:
Solenoid valves
Proportional valves
Relays
Warning lights
Motors
Other actuators
A relatively simple machine may have enough channels on its main controller.
But as more functions are added, I/O requirements can increase rapidly.
For example, a large crane may require signals for:
Boom position
Hydraulic pressure
Outriggers
Limit switches
Load monitoring
Safety devices
Auxiliary equipment
The number of required I/O points can easily exceed the capacity of a single controller.
I/O expansion adds additional input and output channels to an existing control system.
Instead of connecting every device directly to the main controller, additional remote I/O modules can be connected through a communication network such as CAN Bus.
A basic architecture may look like this:
Sensors / Actuators ↓ Remote I/O Module ↓ CAN Bus ↓ Main Controller ↓ HMI
The remote I/O module collects local input signals and transmits the data to the main controller.
At the same time, the controller can send commands through CAN to control outputs on the remote module.
This effectively extends the available I/O capacity of the machine.
This is the most direct reason.
For example, the controller may provide enough channels for the basic machine configuration, but an upgraded model requires:
Additional sensors
More hydraulic valves
Extra switches
New attachments
Instead of redesigning the entire control architecture, engineers can add an I/O module.
OEM manufacturers often build several machines on the same platform.
For example:
Basic Model Main Controller ↓ Standard I/O
while a higher configuration may require:
Advanced Model Main Controller ↓ Standard I/O + Remote I/O
This modular architecture allows the same main controller platform to support different machine configurations.
Large mobile machines can have sensors and actuators located far from the central controller.
Examples include:
Mobile cranes
Concrete pump trucks
Aerial work platforms
Agricultural machines
Mining equipment
Connecting every remote device directly to the central controller can create long and complicated wiring harnesses.
A remote I/O module can instead be installed closer to those devices.
Main Controller │ │ CAN Bus │ Remote I/O ↓ ↓ ↓ Sensor Valve Switch
This creates a distributed control architecture.
A centralized architecture connects most field devices directly to the main controller.
Sensor ───────────────┐ Sensor ───────────────┤ Switch ───────────────┤ Valve ───────────────┼→ Main Controller Valve ───────────────┤ Sensor ───────────────┤ Switch ───────────────┘
As the machine becomes larger, this can require many long individual wires.
A distributed architecture places remote I/O modules near groups of field devices.
Sensors / Valves ↓ Remote I/O │ │ CAN ↓ Main Controller ↑ │ CAN Remote I/O ↑ Sensors / Valves
This architecture can provide greater flexibility for large machines with widely distributed electrical components.
An important advantage of remote I/O expansion is that engineers can add different signal types according to application requirements.
Digital inputs can monitor two-state signals such as:
Limit switches
Push buttons
Proximity switches
Safety switches
Device status signals
They are widely used throughout mobile machinery.
Analog inputs are used for continuously changing signals.
Typical applications include:
Hydraulic pressure
Temperature
Position
Level measurement
Depending on the sensor and module, signal types may include voltage, current, or resistive inputs.
Digital outputs can control:
Relays
Lamps
Solenoid valves
Buzzers
Other on/off loads
Remote output channels allow these devices to be controlled without routing every output wire back to the central controller.
Some remote I/O modules also provide PWM outputs.
These can be used for applications such as:
Proportional hydraulic valves
Speed control
Current-controlled actuators
This allows hydraulic functions to be controlled closer to the valve location.
CAN Bus is particularly suitable for distributed I/O in mobile machinery because it is widely used in vehicle and off-highway control systems.
A typical architecture could include:
→ Remote I/O 1 / Main Controller ─ CAN → Remote I/O 2 \ → Remote I/O 3
Each module provides additional input and output channels in a different area of the machine.
Depending on the system, communication may use:
CANopen
J1939
Proprietary CAN protocols
The main controller receives input information from each module and sends output commands according to the machine control logic.
A mobile crane is a good example of a machine that may benefit from distributed I/O.
The main controller may be installed near the central electrical cabinet.
However, signals are distributed across:
Boom
Outriggers
Hydraulic system
Operator cab
Chassis
Instead of routing every signal directly to the main controller, remote I/O modules can be placed closer to different functional areas.
For example:
Main Controller / | \ CAN CAN CAN ↓ ↓ ↓ Boom I/O Cab I/O Outrigger I/O
The boom I/O module may collect position and limit signals.
The outrigger module may monitor switches and control hydraulic valves.
The cab system may handle operator-related inputs and auxiliary devices.
This creates a modular control architecture around the machine.
OEMs can start with a standard controller and add I/O capacity when required.
This makes it easier to develop multiple machine variants from the same electronic platform.
Remote modules can be positioned according to the physical structure of the machine rather than forcing all wiring toward one controller.
This is particularly useful for large equipment.
New machine functions often require additional sensors or actuators.
With an expandable architecture, engineers can add another remote I/O module instead of redesigning the entire control system.
Locating I/O closer to field devices can reduce the number of long signal wires running through the machine.
Instead, CAN communication connects the remote module to the main controller.
This can make wiring architecture easier to organize and maintain.
Remote I/O modules may be installed outside the protected electrical cabinet.
This means they can be exposed to:
Dust
Water
Vibration
Shock
Temperature changes
Electromagnetic interference
For mobile machinery applications, engineers should therefore consider:
IP protection level
Operating temperature
Connector design
Vibration resistance
Electrical protection
A module designed for factory automation may not necessarily be suitable for installation directly on heavy mobile equipment.
Before adding remote I/O modules, OEM engineers should evaluate:
Required number of additional channels
Digital and analog signal types
PWM output requirements
Maximum output current
CAN protocol
CAN bus load
Installation location
Power supply
Environmental protection
Engineers should also consider future expansion.
Choosing an architecture with some additional capacity can make later machine upgrades easier.
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