to the on-board SPI flash memory IC, which stores the ESP8266’s program memory and
potentially other data.
Back of the Thing
Flipping the Thing over revels a few trace jumpers and test points, which you may find handy
for your application. (Plus a friendly Phant.io logo, to remind you about our data storage
service on data.sparkfun.com.)
Jumpers
Jumper
Label
Default
Setting
Notes
DTR Closed
Allows for auto-reset while programming the ESP8266, but makes
serial debugging difficult.
I2C PU Closed Connects 10kΩ pull-up resistors to the SDA and SCL pins.
FTDI VCC Open
Connects the 3V3 pin on the serial header directly to the
ESP8266's 3.3V supply.
Of these jumpers, the DTR one is the most commonly modified. The DTR output of the FTDI
Basic is used for two purposes: to reset the ESP8266 and pull GPIO0 low (putting the chip in
bootloader mode). Keeping this jumper closed enables programming, but makes debugging
via the Serial Monitor difficult, as the board will reset into bootloader mode whenever the
terminal opens. Using and modifying this jumper is discussed later in this tutorial.
The FTDI_VCC jumper defaults to open to ensure that, if a 3.3V Logic (5V power) FTDI
Cable is used to program the Thing, 5V isn’t accidentally delivered to the IC. Also, most 3.3V
FTDI boards don’t have a lot of juice to supply on the 3.3V bus (they often supply about 50mA
max).
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