The Simplest Network - Making Things Talk - page 45

Figure 2-6
FTDI USB-to-TTL cable. In addition to the transmit, receive,
voltage, and ground connections, it also has connections for
hardware flow control, labeled Request to Send (RTS) and Clear
to Send (CTS). Some devices use this to manage the flow of serial
data.

FTDI
USB-to-TTL Serial Cable

GND
CTS

Black
Brown

Ground
Clear-to-send

Provides voltage output
when plugged into USB port

Vcc
TX

Red
Orange
Yellow

To microcontroller RX

To microcontroller TX RX

RTS Request-to-send

Green

Using an Arduino As a USB-to-Serial Adapter

Arduino boards have a built-in USB-to-serial adapter so that
the microcontroller can communicate with your personal
computer serially. The USB-to-Serial adapter's transmit
pin (TX) is attached to the microcontroller's receive pin
(RX), and vice versa. This means you can bypass the micro-
controller and use the Arduino board as a USB-to-Serial
adapter. There are times when this is handy, like when you
want to communicate directly with the Bluetooth radios
you'll see later in this chapter. To do this, either remove the
microcontroller carefully, or put a sketch on it that does
nothing, like so:

Then connect the desired external serial device as follows:

External serial device's receive pin → Pin 0 of the Arduino
board

External serial device's transmit pin → Pin 1 of the Arduino
board

Now your serial device will communicate directly with the
USB-to-Serial adapter on the Arduino, and the microcon-
troller will be bypassed. When you're ready to use the micro-
controller again, just disconnect the external serial device
and upload a new sketch.

void setup() {}
void loop() {}