Understanding your Photon2

Shamelessly copied from an earlier version of http://docs.particle.io and adapted for Photon2

Table of contents

  1. What is a Particle Photon2?
  2. What do the Buttons do?
  3. What do the LEDs (Light Emitting Diodes - or lights) tell me?
  4. Pins
  5. PWM (Pulse Width Modulation) Pins

The Particle Photon2 (credit: Particle)

What is a Particle Photon2?

The Particle Photon2 is a Wi-Fi development kit for internet-connected hardware. It is, in essence, the “brains” of a connected hardware product or project.

The Photon2 has on board a microcontroller, which is a small, low-cost, low-power computer that can run a single application. The microcontroller runs the show; it runs your software and tells the rest of the Photon2 what to do.

Microcontrollers are particularly good at controlling things; hence the name. They have a set of “pins” (little spider leg type things sticking off the chip) that are called GPIO (General Purpose Input and Output) pins, or I/O pins. They can be hooked to sensors or buttons to listen to the world, or they can be hooked to lights and motors to act upon the world. These microcontroller’s pins have been directly connected to the headers on the sides of the Photon2 so you can easily access them; specifically, the pins labeled D0 to D7 and A0 to A5 are hooked directly to the microcontroller’s GPIO pins.

The microcontroller can also communicate with other chips using common protocols like Serial (also called UART), SPI, or I2C (also called Wire). You can then make the Photon2 more powerful by connecting it to special-purpose chips like motor drivers or shift registers. Sometimes we’ll wrap up these chips on a Shield, an accessory to the Photon2 that makes it easy to extend the Photon2.

The Photon2 also has a Wi-Fi module, which connects it to your local Wi-Fi network in the same way that your computer or smartphone might connect to a Wi-Fi network. The Photon2 is programmed to stay connected to the internet by default, so long as it can find and connect to a network.

When the Photon2 connects to the internet, it establishes a connection to the Particle Cloud. By connecting to the Cloud, the Photon2 becomes accessible from anywhere through a simple REST API. This API is designed to make it very easy to interface with the Photon2 through a web app or mobile app in a secure, private way, so that only you and those you trust can access the Photon2.

What do the Buttons do?

There are two buttons on the Photon: the RESET button (when holding the Photon2 with its USB-port to the top, it’s the button on the right) and the MODE button (on the left).

The RESET button will put the Photon2 in a hard reset, effectively depowering and repowering the microcontroller. This is a good way to restart the application that you’ve downloaded onto the Photon2.

The MODE button serves a few functions:

  • Hold down the MODE button for three seconds to put the Photon2 into Listening mode to connect it to your local Wi-Fi network. The LED should start flashing blue.

  • To put the microcontroller into SAFE mode (where it boots up without loading any code you’ve flashed to it), hold MODE and RESET, release RESET and when the LED displays magenta release the MODE button

  • To put the microcontroller into DFU mode (where you can manually update the firmware via USB), hold MODE and RESET, release RESET and when the LED displays yellow release the MODE button

Diagram of the Photon2 board and it’s pins and buttons! (credit: Particle)

What do the LEDs (Light Emitting Diodes - or lights) tell me?

There is one main RGB LEDs in the middle that shows you the status of the Photon2 internet connection and device status.

The RGB LED could show the following states:

  • Flashing blue: Listening mode, waiting for network information.

  • Flashing green: Connecting to local Wi-Fi network.

  • Flashing cyan: Connecting to Particle Cloud.

  • High-speed flashing cyan: Particle Cloud handshake.

  • Slow breathing cyan: Successfully connected to Particle Cloud.

  • Flashing yellow: Firmware Update Mode, waiting for new code via USB or JTAG.

  • Flashing magenta: Updating firmware.

  • Slow breathing magenta: Safe Mode

  • Slow breathing white: WiFi Off

The RGB LED can also let you know if there were errors in establishing an internet connection. A red LED means an error has occurred. These errors might include:

  1. Two red flashes: Connection failure due to bad internet connection. Check your network connection.

  2. Three red flashes: The Cloud is inaccessible, but the internet connection is fine. Check our Status Board to see if there have been any reported outages on the Particle cloud.

  3. Four red flashes: The Cloud was reached but the secure handshake failed.

  4. Flashing yellow/red: Bad credentials for the Particle Cloud.

Pins

The Photon2 has 24 pins that you can connect a circuit to. These pins are:

  • VUSB: To power the Photon2 off an unregulated power source with a voltage between 3.6V and 6V, or, if you’re powering the Photon2 over USB, this pin can be used as 5V V~OUT~ to power external components. In this case consider the current limitation imposed by your USB power source (e.g. max. 500mA for standard USB 2.0 ports). Avoid powering the Photon2 via USB and V~IN~ concurrently.

  • Li+: This pin is internally connected to the positive terminal of the LiPo battery connector.

  • 3V3: This pin will output a regulated 3.3V power rail that can be used to power any components outside the Photon2. (Also, if you have your own 3.3V regulated power source, you can plug it in here to power the Photon2).

  • GND: These pins are your ground pins.

  • RST: You can reset the Photon2 (same as pressing the RESET button) by connecting this pin to GND.

  • D2 to D8: These are the bread and butter of the Particle Photon2: GPIO (General Purpose Input/Output) pins. They’re labeled “D” because they are “Digital” pins, meaning they can’t read the values of analog sensors.

  • A0 to A5: These pins are 6 more GPIO pins, to bring the total count up to 16. These pins are just like D2 to D8, but they are “Analog” pins, which means they can read the values of analog sensors (technically speaking they have an ADC peripheral). As with the Digital pins, some of these pins have additional peripherals available. A0-A5 are PWM-able

  • TX and RX: These pins are for communicating over Serial/UART. TX represents the transmitting pin, and RX represents the receiving pin.

  • SDA & SLC: Primarily used as data pin and clock pin for I2C, but can also be used as a digital GPIO.

  • MO,MI & SCK: Primarily used as SPI interface pins, but can also be used as a digital GPIO.

PWM (Pulse Width Modulation) Pins

When you want to use the analogWrite() function on the Photon2, for instance to smoothly dim the brightness of LEDs, you need to use pins that have a timer peripheral. People often call these PWM pins, since what they do is called Pulse Width Modulation. All of the Photon’s Digital and Analog Pins can be used to perform PWM.

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