dfrobot FireBeetle ESP8266 IoT Microcontroller (Supports Wi-Fi)

AI context

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

PART: DFRobot FireBeetle ESP8266 IoT Microcontroller (Supports Wi-Fi), SKU DFR0489, 58 mm x 29 mm with 53 mm x 24 mm mounting holes, 24 g, built on an Espressif ESP8266EX: 32-bit Tensilica L106, 80 MHz default and 160 MHz maximum, 50 KB SRAM available to the sketch, 16 MB external SPI flash on board, 10-bit SAR ADC and 802.11 b/g/n Wi-Fi on 2.4 GHz only. It adds a micro-USB socket, a CH340C USB-serial bridge with an STM8S003 auto-download circuit, a TP4056 Li-ion charger, a 3.3 V LDO and two 18-pin 2.54 mm header rows (36 holes).
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: IO3 (D0, RXD), IO1 (D1, TXD), IO13 (D2), IO10 (D3), IO15 (D4), IO2 (D5), IO5 (D6), IO4 (D7), IO0 (D8), IO12 (D9), NC, NC, NC, NC, GND, AREF, 3V3, VCC. Right row, pads 19-36: A0, NC, NC, NC, NC, NC, IO0, SCK (IO14), MOSI (IO13), MISO (IO12), SDA (IO4), SCL (IO5), NC, NC, NC, NC, NC, RST. Ten pads carry the Dx aliases D0-D9 and those aliases are DFRobot's own: D0 is GPIO3 and D1 is GPIO1, which are the UART0 RX and TX lines, so the serial console occupies two of the ten. GPIO4, GPIO5, GPIO12 and GPIO13 each appear on both rows (as SDA/SCL/SCK and as D7/D6/D9/D2 respectively) and the two pads of each pair are one net - do not use them as two independent signals. Only one analogue input exists, A0, and there is no AREF source on the board.
I2C: SDA is GPIO4 and SCL is GPIO5, and both are broken out twice - as GPIO4/GPIO5 on the left row and as SDA/SCL on the right row. There is no I2C device on the board, so no fixed addresses exist to record.
SUPPLY: the ESP8266EX itself runs 2.5 V to 3.6 V and the board regulates 3.3 V from a micro-USB 5 V input or a 3.7 V LiPo on the JST connector, with a stated input range of 3.3 V to 5 V. DFRobot rates the 3.3 V output at 600 mA maximum discharge and the charger at 500 mA maximum charge, quotes 80 mA average operating current and 46 uA in low-power mode.
LOGIC AND LIMITS: logic is 3.3 V with no level shifting anywhere on the header pins - the ESP8266EX table gives VIL of -0.3 V to 0.25 x VIO, VIH of 0.75 x VIO up to 3.6 V, and 12 mA maximum per IO, so a 5 V sensor output must be divided or shifted before it reaches any pad. The ADC (TOUT) accepts 0 V to 1.0 V when driven from outside, which is the ceiling on the A0 pad.
REFERENCE CIRCUIT: the board carries its own regulation, charging and USB-serial, so a host needs only 5 V on the micro-USB or a cell on the battery connector. 10 kOhm pull-ups to 3.3 V are fitted on both I2C lines, on EN, and across the reset switch, so a sensor with its own pull-ups is paralleled rather than required; add nothing unless you are chaining many devices. The two UART lines run through 470 Ohm series resistors to the CH340C. A0 reaches the ADC through a 220 kOhm series resistor into the same node as the on-board battery divider (320 kOhm from the battery rail, 100 kOhm to ground), which is scaled so a 4.2 V cell lands just under the 1.0 V ADC full scale.
TRAPS: the VCC pad is the raw rail - 5 V under USB and about 3.7 V on a LiPo - not a regulated 3.3 V, and feeding 5 V back into it while on battery is not what the power path expects. Because A0 shares the battery divider node, an external signal on A0 is attenuated and loaded by that network and cannot be read independently of the battery sense. GPIO0, GPIO2 and GPIO15 are the boot-mode straps; GPIO0 is pulled low by the STM8/CH340 auto-download circuit at reset, so anything wired to D8 must not fight that pull-down. The ESP8266EX data sheet warns that U0TXD must not be pulled low externally during power-up, which is the D1 pad. Five holes on the right row and four on the left are NC and carry no net at all. DFRobot lists operating temperature as -40 to +85 C in one line of the same table and -10 to +55 C in another, so neither figure is quoted here. The CHG LED blinks with no battery connected, is lit while charging and goes dark when the charge completes. Espressif marks the ESP8266EX not recommended for new designs in the current data sheet.