Photon

The Photon is a tiny WiFi development kit based around USI's WM-N-BM-09 module. This module is a combination of Broadcom's BCM43362 WiFi radio and a STM32F205G microcontroller.

The Photon has a similar footprint and is as close to drop-in compatible as possible with the Spark Core.

Some highlights of the USI module:

1. IEEE 802.11b/g/n
2. Soft AP mode - read smooth WiFi setup process
3. STM32F205G
   • 1 MB Flash
   • 128KB RAM
   • 120 MHz clock
4. Measures 12mm x 11mm x 1.3mm

Compared to the Spark Core, the Photon introduces some additional hardware features and changes:

1. Pin 3V3* is now replaced with VBAT. This pin can be used to power the internal RTC, backup registers and SRAM when the module is put in standby mode.
2. Pins D1 and D2 can also be used for CAN communication (TX and RX respectively).
3. Pin A3 now features a DAC (channel 2)
4. Pin A6 is changed to DAC and exposes a DAC (channel 1).
5. Pin A7 is changed to WKP (Wakeup). This pin can be used as a standard GPIO, ADC input, PWM or to WAKEUP (rising edge) the module from sleep/standby modes.

A detailed description of the pin mapping can be found in the pin-mapping folder of this repository.

• Sheet 1: Overview of the pin-out.
• Sheet 2: Detailed description of USI module pin-out and its internal mapping to the microcontroller and WiFi radio.

Pin Descriptions:

• VIN: This is the power supply pin to the Photon with a voltage range of 3.6 to 5.5VDC (internally regulated down to 3.3VDC). When the Photon is powered via its USB port, this pin will ouput a voltage of approximately 4.7VDC. Why 4.7 and not 5? Well, the actual voltage will be the USB voltage, which is normally 5, minus the forward voltage drop (0.3V) of the protection diode.
• RST: This is an active-low reset pin for the Photon.
• VBAT: Supply to the internal RTC, backup registers and SRAM (1.8 to 3.3VDC).
• 3V3: This pin is the output of the on-board regulator and is internally connected to the VDD of the WiFi module. When powering the Photon via VIN or the USB port, this pin will output a voltage of 3.3VDC. This pin can also be used to power the Photon directly (max input 3.3VDC). NOTE: When powering the Photon via this pin, do not put power on the VIN pin.
• WKP: This is an active-high input that allows you to wakeup the module from sleep/deep sleep modes. When not used as a WAKEUP, this pin can also be used as a digital GPIO, ADC input or PWM.
• D0 - D7: These are digital only GPIO pins.
• A0 - A5: These can be used as digital GPIOs or as ADC inputs.
• DAC: This pin can be used as a digital GPIO, ADC input or as a DAC ouput.
• RX: Primarily used as UART RX, but can also be used as a digital GPIO, ADC input or PWM.
• TX: Primarily used as UART TX, but can also be used as a digital GPIO, ADC input or PWM.

Please review the spreadsheet under the pin-mapping folder to better understand the alternate functions of the GPIO pins.

Eagle (schematic and pcb layout):

Under the eagle folder, you'll find the history of Photon designs.

1. cam-drc: Contains CAM Jobs (for creating gerbers) and DRC (Design Rule) files.
2. photon_v001: The initial photon design. This version of the design uses the same dimensions as the Spark Core and provides through-hole headers for mounting.
3. photon_v010: Several versions later, numerous tweaks and additions to the schematic, smaller less blinding RGB LED, aligned D7 LED with D7 pin, new SMPS voltage regulator, castellated and non-castellated have been merged, new slightly larger higher gain antenna, Bluetooth Co-existance pins are broken out to pads for a 1.27mm pitch (0.050") connector, pads on the bottom side of the board were added for the RGB LED, and MODE button connections and are centered on the 0.1" grid, and RF switch for software selection of u.FL vs Chip Ant. RF Test board's for versions are included to make tuning of matching components in RF stage easier. There is a second Photon design here with antenna scooted to the left 0.027" to give more clearance between D0 pin and antenna. C1 in Pi filter was removed to make room for this tighter layout.
4. photon_v019: Several more versions later, numerous tweaks and additions to the schematic, WM-N-BM-09 soldermask updated, added some GND vias, MODE button label changed to SETUP, increased width of top and bottom (short) sides of PCB 20 mils to allow for v-score (overall board height is now 1.44"), SETUP and RESET buttons and RGB led are not centered on the 0.1" grid anymore but they are all still inline with each other, RF switch was changed to a much smaller 1mm version, 0201 dc blocking capacitors added to all RF ports, Pi filter was tuned to match antenna to 50 ohm impedance, half of the pads on the bottom were enlarged to 60 mils square, added fabrication spec.

#License

Designed by Spark IO. Distributed under a Creative Commons Attribution, Share-Alike license. Development kits based on this product should be distributed under a similar license. Commercial products using the Photon as a reference design need not comply with this license; further questions can be sent to [email protected]. Check license.txt for more information.