The four pins

What is on the board

A microphone capsule in a foam ring, eight small parts round it, and a four-pin header along the bottom edge. The header is right-angled, so the pins point out past the edge of the board and it lies flat in a breadboard or on a cable.

The capsule is an electret microphone, 9.7 mm across, and the only part that hears anything. The small parts are its supply, its filters and a one-transistor amplifier. A capsule and one transistor goes through them.

The four names

GND is on the square pad. The capsule's ground lead, the transistor's emitter and three of the small parts end here.

VCC feeds three resistors: one powers the capsule, one biases the transistor, and SIGNAL hangs from the third. Match it to your board: 3V3 beside an ESP32, ESP32-S3 or Pico, 5V beside an Uno. A loud sound can take SIGNAL up to VCC itself.

NC means not connected, and on this board it means it literally. The net list, the list of every electrical connection on the board, does not mention it.

SIGNAL is the transistor's output. In silence it rests at one voltage, somewhere between the rails, and sound makes it swing above and below that voltage. It goes to an analog pin, not a digital one. It is not a loudness level: louder does not simply mean higher.

No light on the board

Some TinkerBlock blocks carry an LED that shows what the output is doing. This one does not, and it has no comparator either, so there is no on-off output and no knob to set one. The first reading is the test: a still line in the Serial Plotter that jumps when you clap.

The back of the board

Turned over, the order reverses. The square pad is on the right, and it is still GND. The back prints TK27 ANALOG MIC SENSOR and DETECTS SOUND INTENSITY, but no pin names. The intensity is something your sketch works out from the swing; the board itself only passes the swing on.