Standard Modes

These modes are the typical behaviors you will see from your Core on a regular basis. They are the light patterns of a healthy Core.

Here's the typical pattern of a Core after power up.


When it is breathing cyan, your Core is happily connected to the Internet. When it is in this mode, you can call functions and flash code.

OTA Firmware Update

If your Core is blinking magenta (red and blue at the same time), it is currently loading an app or updating its firmware. This state is triggered by a firmware update or by flashing code from the Web IDE or Desktop IDE. You might see this mode when you connect your Core to the cloud for the first time.

Note that, if you enter this mode by holding MODE on boot, blinking magenta indicates that letting go of the MODE button will enter safe mode to connect to the cloud and not run application firmware.

Looking For Internet

If your Core is blinking green, it is trying to connect to Wi-Fi.

More information

Connecting to the Cloud

When the Core is in the process of connecting to the cloud, it will rapidly blink cyan. You often see this mode when you first connect your Core to a network, after it has just blinked green.

Listening Mode

When your Core is in Listening Mode, it is waiting for your input to connect to Wi-Fi. Your Core needs to be in Listening Mode in order to begin connecting with the Mobile App or over USB.

To put your Core in Listening Mode, hold the MODE button for three seconds, until the RGB LED begins blinking blue.

Wi-Fi Network Reset

To erase the stored Wi-Fi networks on your Core, hold the MODE button for about ten seconds, until the RGB LED blinks blue rapidly.

Wi-Fi Off

If your Core is breathing white, the Wi-Fi module is off. You might see this mode if:

  • You have set your module to MANUAL or SEMI_AUTOMATIC in your user firmware
  • You have called in your user firmware

Safe Mode

Safe mode, breathing magenta (red and blue at the same time), connects the Core to the cloud, but does not run any application firmware. This mode is one of the most useful for development or for troubleshooting. If something goes wrong with the app you loaded onto your device, you can set your device to Safe Mode. This runs the Device OS but doesn't execute any application code, which can be useful if the application code contains bugs that stop the device from connecting to the cloud.

The Core indicates that it is in Safe Mode with the LED breathing magenta.

To put your device in Safe Mode:

  1. Hold down BOTH buttons
  2. Release only the RST button, while holding down the MODE button.
  3. Wait for the LED to start blinking magenta
  4. Release the MODE button

Before entering safe mode, the Core will proceed through the normal steps of connecting to the cloud; blinking green, blinking cyan, and fast blinking cyan. If you're unable to connect to the cloud, you won't be able to enter safe mode.

The device will itself automatically enter safe mode if there is no application code flashed to the device or when the application is not valid.

DFU Mode (Device Firmware Upgrade)

If you wish to program your Core with a custom firmware via USB, you'll need to use this mode. This mode triggers the on-board bootloader that accepts firmware binary files via dfu-util

Installation tutorial can be found here.

And a usage guide here.

To enter DFU Mode:

  1. Hold down BOTH buttons
  2. Release only the RST button, while holding down the MODE button.
  3. Wait for the LED to start flashing yellow
  4. Release the MODE button "

The Core now is in the DFU mode.

DFU mode requires device drivers under Windows. These should automatically be installed by the Particle CLI installer, but if you think you are having driver issues, there are additional DFU troubleshooting tips here.

Some users have reported issues with dfu-util on a USB3 ports (typically the blue ones). Use a USB2 port if the USB3 port doesn't work.

Factory Reset

A factory reset restores the firmware on the Core to the default Tinker app and clears all your Wi-Fi credentials.


The procedure is same as the one described above (DFU Mode), but in this case you should continue holding down the MODE button until you see the Core change from blinking yellow to blinking white. Then release the button. The Core should begin after the factory reset is complete.

  1. Hold down BOTH buttons
  2. Release only the RST button, while holding down the MODE button.
  3. Wait for the LED to start blinking yellow (continue to hold the MODE button)
  4. The LED will turn solid white (continue to hold the MODE button)
  5. Finally, the LED will turn blink white rapidly
  6. Release the MODE button

You can reset Wi-Fi credentials by performing a Wi-Fi Network Reset.

Troubleshooting Modes

These modes let you know about more atypical issues your Core might be exhibiting. Use this section to troubleshoot strange colors you might see from your Core.

Wi-Fi Module Not Connected

If the Wi-Fi module is on but not connected to a network, your Core will be breathing blue. Note that this will be dark blue and not cyan.

Cloud Not Connected

When your Core is connected to Wi-Fi but not to the cloud, it will be breathing green.

More information


Using the Signal option in the Web IDE, or the particle cloud nyan CLI command, you can have a device's status LED display a rainbow pattern. This is handy if you have multiple devices nearby and are not sure which one is which.

Blinking red indicates various errors.

While connecting to the Cloud, the RGB LED will be blinking cyan followed by:

  • 1 orange blink: Decryption error.
  • 2 orange blinks: Could not reach the internet.
  • 3 orange blinks: Connected to the internet, but could not reach the Particle Device Cloud. This sometimes is seen as yellow or red and indicates bad server keys.
  • 1 magenta blink: Authentication error.
  • 1 red blink: Generic handshake error. The device could have the wrong keys or has just encountered a generic error in the handshake process.

Repair instructions

Red Flash SOS

Is your Core blinking red? Oh no!

A pattern of more than 10 red blinks is caused by the firmware crashing. The pattern is 3 short blinks, 3 long blinks, 3 short blinks (SOS pattern), followed by a number of blinks that depend on the error, then the SOS pattern again.

Perform a factory reset, tweak your firmware and try again!

There are a number of other red blink codes that may be expressed after the SOS blinks:

  1. Hard fault
  2. Non-maskable interrupt fault
  3. Memory Manager fault
  4. Bus fault
  5. Usage fault
  6. Invalid length
  7. Exit
  8. Out of heap memory
  9. SPI over-run
  10. Assertion failure
  11. Invalid case
  12. Pure virtual call
  13. Stack overflow

The two most common ones are:

Hard Fault (1 blink between 2 SOS patterns)

Some causes of hard fault include:

  • Using an invalid pointer.
  • Memory corruption caused by freeing memory twice, overwriting the end of a block of memory, etc.
  • Making Wire (I2C) calls without calling Wire.begin().

Out of heap memory (8 blinks between 2 SOS patterns)

If your Core crashes repeatedly with an SOS code, first try recovering with Safe Mode and flashing Tinker with the CLI to see if it was something recently added in your user application.

particle flash <mydevice> tinker

Some tips for reducing the memory used by your firmware can be found here.

Stack overflow (13 blinks between 2 SOS patterns)

Stack overflow occurs when you try to store too much data on the stack. The size is quite limited, and storing large temporary objects on the stack can cause problems.

  • Main loop thread: 6144 bytes
  • Software timer callbacks: 1024 bytes

Solid colors

Solid colors are rare. There are two expected situations:

  • Solid white if you are in the middle of a factory reset.
  • Solid magenta if you are loading code in ymodem serial mode.

In most cases, solid colors are the side effect of a bug. If code crashes or infinitely loops with interrupts disabled, it's possible that the LED animation will stop. The color of the LED is the color it last was before failure. So for example, it could be solid cyan if it was previously breathing cyan, or solid red if it was trying to output an SOS pattern.

No status LED

If you power up your Core and the status LED never comes on and the small blue led next to pin D7 is on dimly, you have a missing or corrupted bootloader.

This can be corrected using a JTAG/SWD programmer if you have one. Otherwise, you should contact support.