Electronics | CNCAD V-1.0

Signal flow

From software command to motor movement

The CNC Driver does not move the machine directly. It sends step and direction states through the computer output pins. The electronics convert those low-current logic signals into controlled power for the motors, while the sensor and protection circuits help prevent movement outside the expected limits.

This approach keeps the project easy to study: every axis can be understood as a chain of software instruction, logic signal, driver output, and mechanical displacement.

Parallel port data bus control for the X axis motor — Parallel port control path for the X axis motor.

Circuit blocks

Main electronic modules

Connection interface

Adapts the computer output to the control board. It separates the software layer from the power stage and gives the project a clear place to organize each signal.

Monitor circuit

Provides a basic view of the operating state. Monitoring is useful while testing because it shows whether signals are reaching the expected part of the circuit.

Protection circuit

Helps avoid unsafe states before they reach the driver stage. In a CNC machine this matters because a wrong signal can move an axis in the wrong direction or hold a motor energized.

H-bridges

Control current direction through the motor coils. This allows the circuit to drive bipolar stepper motors and reverse movement when the driver changes direction.

Parallel port

Uses the DB25 output pins as the communication path between the GNU/Linux software and the electronics. Each pin can represent a step, direction, enable, or control state.

Stepper motors

Move the axes in small increments. This makes them practical for a prototype router because the software can count steps and translate coordinate changes into physical displacement.

Logic gates

Use simple digital logic to combine or validate signals before they reach the drivers. This keeps control behavior predictable and easier to troubleshoot.

Sensors

Provide feedback from the machine. Limit or position sensors help the driver understand when an axis reaches a defined point or needs to stop.

Interlock circuit diagram — Interlock logic used as part of the protection stage.

Protection and interlock

Keeping the control stage predictable

The interlock section acts as a safety layer between command signals and motor output. Its purpose is to prevent contradictory or unexpected states from reaching the motor drivers.

For a small educational CNC router, this is especially important during manual control and initialization. The operator may test one axis at a time, reverse directions, or move the tool close to the material, so the circuit should make those operations easier to observe and less likely to damage the mechanism.

Motor driving

Driver circuits for bipolar stepper motors

Bipolar stepper motors need their coil current to change direction in a controlled sequence. The H-bridge and L293-style driver references show how the project can energize the coils from logic-level commands.

The CNC Driver software decides when an axis should move. The electronics provide the electrical force needed to make that movement happen, one step at a time.