If you have connected your mBot to your PC/Mac/Chromebook via USB and you cannot get the mBlock software to connect to your mBot, try the following:

1. Verify that mBot is turned on.

2. Verify that the Arduino driver is installed.

The microcontroller at the heart of mBot is called mCore and is based on the popular Arduino Uno microcontroller; in fact, it uses the same software driver. The mBlock software uses the Arduino driver to “talk” to mBot. If the Arduino driver is missing – which may be the case if you just installed mBlock, updated your computer, or otherwise made system changes – you will need to install it before mBlock will connect to mBot.

Install the Arduino driver by choosing “Install Arduino Driver” from the Connect menu in mBlock.

On a Mac? Also see Why won't my Mac computer connect to my mBot (mBlock 3 only)?

3. Verify that the correct COM (USB) port has been selected.

From the Connect menu, choose Serial Port and then select the COM (USB) port to which mBot is connected.

If you are not sure which COM port is the correct port, unplug your the USB cable from your computer/Chromebook, close mBlock, and then restart it. Choose the Serial Port option in the Connect menu and take note of which COM ports are recognized. Then, with the mBot turned on, re-connect the USB cable. mBlock will update the list with the new connection. Select that new COM port.

When mBlock recognizes and connects to mBot, you will see two indications:
*The window title will change from “Disconnected” to “Serial Port Connected”.
*The indicator circle next to the mBot section of the Robots palette will change from red to green.

NOTE: The list of COM ports populated by mBlock is a list of all USB ports on your computer currently being used, either by an mBot or other USB device (keyboard, mouse, etc.) Thus, it is possible to select an incorrect COM port. When you do, mBlock will report that it is “connected” to mBot. But if you have chosen the wrong COM port, the “Upload to Arduino”, “Reset Default Program”, or “Upgrade Firmware” functions will fail. Follow the procedure described above to identify the correct COM port.

If you have tried the preceding steps and mBlock will still not connect to mBot, investigate the additional, but rare, problems:
*Is the USB cable damaged? Try swapping it out for a different cable.
*Is the correct controller selected in mBlock? In the Boards menu, verify that “mBot (mCore)” has been selected.

mBot Troubleshooting and FAQs