How to communicate between a Doosan robot and a microcontroller using a transistor

💡 How-to
1

How-to: Communicating between a Doosan robot and a microcontroller using a transistor

Goal

This how-to explains how to send a simple digital signal between a microcontroller and a Doosan robot toolhead using a transistor.

In our project, we needed a Doosan M1013 robot to communicate with a microcontroller. The microcontroller controlled sensors, servos and gripper logic, while the robot needed a simple digital signal to continue or stop its program.

The problem is that the Doosan toolhead uses 24V digital I/O, while an ESP32 or Arduino uses 3.3V or 5V logic. These cannot be connected directly.

This how-to shows a solution using a transistor.

We used:

  • Doosan M1013 robot
  • ESP32 microcontroller
  • Doosan tool digital input
  • 2N2222 NPN transistor
  • Resistors

Why a transistor is needed

A Doosan digital input expects a 24V signal.

A microcontroller output pin gives only 3.3V or 5V and cannot safely drive the robot input directly.

The transistor works as a small electronic switch:

  1. Microcontroller output LOW → transistor off
  2. Microcontroller output HIGH → transistor on
  3. Transistor off → Doosan input is pulled to 24V
  4. Transistor on → Doosan input is pulled to GND

This means the signal is inverted.

Wiring

The Doosan digital input point is pulled up to 24V using a resistor. The transistor can pull this point down to GND.

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Connections:

collector → Doosan digital input
emitter → Doosan GND
base → microcontroller output through a resistor

Doosan GND → microcontroller GND
Doosan +24V → pull-up resistor → Doosan digital input

Do not connect the Doosan digital input directly to +24V without a resistor in this transistor setup.

Resistor values

Recommended values:

Pull-up from +24V to Doosan DI: around 10k to 15k
Base resistor from ESP32/Arduino output to 2N2222 base: around 10k to 39k

This can be used as the pull-up from Doosan +24V to the Doosan digital input.

Logic

The signal is inverted:

Microcontroller output LOW → transistor off → Doosan DI HIGH
Microcontroller output HIGH → transistor on → Doosan DI LOW

So in the robot software or microcontroller software, the logic may need to be inverted.

ESP32 / Arduino test code

This example toggles the output every 3 seconds.

#include <Arduino.h>

const int DOOSAN_SIGNAL_PIN = 15;

void setup()
{
    Serial.begin(115200);

    pinMode(DOOSAN_SIGNAL_PIN, OUTPUT);
    digitalWrite(DOOSAN_SIGNAL_PIN, LOW);
}

void loop()
{
    Serial.println("output LOW -> Doosan DI  HIGH");
    digitalWrite(DOOSAN_SIGNAL_PIN, LOW);
    delay(3000);

    Serial.println("output HIGH -> Doosan DI LOW");
    digitalWrite(DOOSAN_SIGNAL_PIN, HIGH);
    delay(3000);
}

Testing with a multimeter

Before connecting the Doosan digital input, test the collector point.

Measure between:

Red probe   -> collector / Doosan DI point
Black probe -> GND

Expected result:

Microcontroller output LOW  -> about 24V
Microcontroller output HIGH -> about 0V

If this works, the signal is safe to connect to the Doosan digital input.

Reading the input on the Doosan side

In C++ with DRFL, the tool digital input can be read with get_tool_digital_input.

Example:

int input_value = robot.get_tool_digital_input(
    static_cast<GPIO_TOOL_DIGITAL_INDEX>(3)
);

if (input_value == 1)
{
    std::cout << "Doosan input is HIGH" << std::endl;
}
else if (input_value == 0)
{
    std::cout << "Doosan input is LOW" << std::endl;
}
else
{
    std::cout << "Error reading Doosan input" << std::endl;
}
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