Why doesn't the Arduino work when connected?
Why doesn't the Arduino work when connected?
If the Arduino does not work when connected to the computer, the most common cause is not the board itself, but a problem with USB communication, Controllers or the bootloader. Typical symptoms include LEDs not responding, the COM port not appearing on the system or errors during program upload. In most cases, the fault is due to a misconfiguration or damage to the Cables, rather than a failure of the microcontroller.
Lack of communication with the computer - Controllers and COM port
When you connect the Arduino to your computer, the operating system should automatically recognise the device and assign it the serial (COM) port. If the port does not appear, it means that the computer is unable to establish communication with the USB-UART converter chip. On Arduino Uno boards, this role is performed by ATmega16U2. In order for the Arduino to be detected correctly, the appropriate controllers are required. Windows installs them automatically only for original boards; for clones, they must be downloaded and installed manually from the manufacturer's website. If the drivers are missing, the Arduino remains invisible and the IDE is unable to upload the program. On Linux and macOS, the problem occurs less frequently, but it is sometimes necessary to add a user to the dialout group to access the serial port. It is also worth making sure that the correct COM port and board model is selected in the Arduino IDE environment. Often the software will remember previous settings that do not correspond to the currently connected device, resulting in an error message when compiling or uploading the program.
Damaged or unsuitable USB cable
A common source of the problem is USB cable, especially if it comes from a phone charging kit. Many such cables only allow the transfer of power, not data. As a result, the board lights up with a power Diodes, but the computer does not detect it. Even if the cable has adequate functionality, damage to the transmission wire can result in intermittent communication or programming errors. The best solution is to use a short, shielded A-B type USB cable (for Uno) or a mini/micro USB cable (for Nano) that supports both data and power transmission.
Lack of or damaged bootloader
If the COM port is visible but the software cannot be uploaded, the cause may be lack of bootloader in the microcontroller. The bootloader is a small piece of software stored in the microcontroller's memory that allows it to accept code from a computer via the USB port. If the bootloader is missing, the board will not respond to attempts to upload sketches, even though it is working correctly on the hardware side. In such a situation, the bootloader should be uploaded again, using external ISP programmer (e.g. USBasp) or another Arduino board working in programmer mode. This operation restores full functionality of the board and is done once.
Other causes - power supply and IDE configuration
Sometimes the Arduino does not work due to incorrect power supply. Too low a voltage from the USB port (e.g. through a poor hub or damaged socket) can prevent the microcontroller from starting or cause the board to reset. It is worth checking that the PWR Diodes are lit steadily - this is a sign that 5V is present. Errors can also result from incorrect selection of the board model in the Arduino IDE. Arduino Nano, depending on version, may use a different type of processor or bootloader ("Old Bootloader"), which should be taken into account in menu Tools → Processor.
Transfer Multisort Elektronik (TME) is one of the world’s largest global distributors of electronic components, electrotechnical parts, workshop equipment, and industrial automation. The catalog includes over 1,500,000 products from 1,300 leading manufacturers. TME’s modern logistics centers in Łódź and Rzgów (Poland), with a combined area of over 40,000 m², ship nearly 6,000 packages daily to customers in more than 150 countries.
TME also invests in the development of knowledge and skills of young engineers and electronics enthusiasts through the TME Education project, and supports the tech community by organizing the TechMasterEvent series, promoting innovation and experience exchange.
