He needed a way to snoop on the back and forth serial communications ... serial cable containing the TX, RX, DTR, and GND wires. This cable connects the Arduino to the ESP8266 WiFi module.

On-board jumpers allow the transmitter and receiver to be connected to a choice of Arduino I/O pins – default is Tx is connected to UART Serial pin 1 and Rx to UART Serial pin 0. The associated ...

Arduino Micro has some extra leds that it is tricky to programme. Like almost all Arduinos, has a built-in led – the green one on the left in the photo. And it has a pair of yellow leds – called TX ...