dfrobot FireBeetle 328P Low-Power Arduino Board (BLE 4.1)

AI context

Dense context for pasting into a model prompt — addresses, pinout, voltages, tolerances and the vendor's reference circuit.

PART: DFRobot FireBeetle 328P Low-Power Arduino Board (BLE 4.1), SKU DFR0492, 58 mm x 29 mm, two 18-pin 2.54 mm header rows (36 holes). It is an ATmega328P board with a separate BLE 4.1 module on the same PCB: 14 digital pads D0-D13, six analogue inputs A0-A5, one SPI, one I2C and one UART, with the on-board LED on D13 (DFRobot names it LED_BUILTIN). The ATmega328P runs from 3.3 V and DFRobot ships it with the Arduino Pro or Pro Mini bootloader for ATmega328 at 3.3 V and 8 MHz.
PINOUT: DFRobot prints no pad numbers, so the numbers here are this entry's own - left row 1-18 first, then right row 19-36, both starting at the antenna end with the micro-USB at the far end. Left row, pads 1-18: D0 (RXD), D1 (TXD), D2, D3 (PWM), D4, D5 (PWM), D6 (PWM), D7, D8, D9 (PWM), D10 (PWM), D11 (PWM), D12, D13, GND, AREF, 3V3, VCC. Right row, pads 19-36: A0, A1, A2, A3, A4, A5, NC, SCK, MOSI, MISO, SDA, SCL, NC, NC, NC, NC, NC, RST. The six pads DFRobot marks PWM are D3, D5, D6, D9, D10 and D11, and the ATmega328P has six timer compare outputs across three timers. The 14 digital and six analogue pads match DFRobot's own count of 14 digital and 6 analogue interfaces.
I2C AND BUSES: the right row carries SDA and SCL as pads of their own, and separately carries A4 and A5. On the silicon these are not independent - the ATmega328P's pin table gives PC4 as ADC4/SDA and PC5 as ADC5/SCL - so the SDA pad and A4, and the SCL pad and A5, reach the same two pins, and using an analogue input on A4 or A5 takes the I2C bus with it. SPI is SCK, MOSI and MISO on the right row (PB5, PB3 and PB4 on the chip) with no dedicated chip-select pad. UART is D0/D1, which is also the pair the BLE module and the USB-serial bridge share. There is no I2C device on the board, so no fixed address exists to record.
SUPPLY: operating voltage 3.3 V, with the VCC rail stated at 3.7 V to 5.5 V and a 3.7 V LiPo on the battery connector. DFRobot rates the 3.3 V LDO output at 600 mA maximum discharge and the charger at 400 mA maximum charge, and quotes 25 uA in power-down against 70 uA with the interrupt enabled.
LOGIC AND LIMITS: the ATmega328P in this build is a 3.3 V part, so its I/O swing is 3.3 V and not 5 V - DFRobot's spec table lists the VCC I/O range, not the logic level, and feeding 5 V into a digital pad is outside the chip's ratings even though the bare ATmega328P can run at 5 V. The device data sheet gives -0.5 V to VCC+0.5 V on any pin except RESET (-0.5 V to +13.0 V), 6.0 V maximum operating voltage, 40 mA DC per I/O pin, 200 mA total on VCC and GND, and an operating range of 1.8 V to 5.5 V for the chip itself.
REFERENCE CIRCUIT: DFRobot publishes no schematic for this board, so decoupling and pull-up values cannot be quoted from a vendor drawing and none are recorded here. What the vendor does document is the handshake between the two chips: the BLE 4.1 module wakes the ATmega328P by driving D2 high, and the ATmega328P wakes the BLE module by pulling D3 low, so both lines are claimed by that function before any user circuit.
TRAPS: the BLE module occupies the ATmega328P's serial port, so a Bluetooth connection must be dropped before an upload or the sketch will not download. The bootloader is the 3.3 V / 8 MHz Pro Mini one, which cannot keep up with 115200 baud - DFRobot recommends 9600 and says anything faster comes back as gibberish. The Arduino IDE lists the port as an Arduino UNO; the board to select is Arduino Pro or Pro Mini, ATmega328, 3.3 V, 8 MHz. Bluetooth device IDs are assigned by connection order (ID1 to ID4) and cannot be changed, so connect the central first. HID, iBeacon and tree networking are listed as under development, not available. D9 to D13 are on the left row while the SPI pads are on the right row, so a shield built for an Uno's header order will not map across.