The four pins
Four pins, three of them wired. GND and VCC power the block, SIGNAL goes HIGH for a moment each time the spring touches its rod, and NC is connected to nothing. The board has a pull-down, not a pull-up, and it prints ACTIVE HIGH to say so.
What is on the board
The spring switch lying flat along the top, three small parts in a row under it, a red LED under those, 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 panel.
The row of three, left to right, is R4, the 1 kΩ resistor for the LED; R3, the 10 kΩ pull-down; and C1, the 100 nF capacitor, which is the brown one. The LED sits under them, above the header. The switch is the tallest part, about 5.6 mm above the board.
The four names
GND is on the square pad. The pull-down, the capacitor and the LED's resistor all return here.
VCC goes to one leg of the switch and nowhere else. Whatever you connect to VCC is what your pin receives while the spring touches the rod, which is why VCC sets the voltage has its own article.
NC means not connected, and on this board it means it literally: no trace reaches that pad.
SIGNAL is the output, on the switch's other leg. At rest it sits at 0 V and your board reads LOW. Each time a knock swings the spring onto the rod, it goes to VCC for a moment and your board reads HIGH. HIGH means knock, and the front of the board says so in a box: ACTIVE HIGH.
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 TK28, the number on the box, and no pin names.
When it does not work
Hold the board with the clear switch at the top and the header pins pointing down. Read GND, VCC, NC, SIGNAL from left to right. GND is also the square pad, which is the one mark that survives when the labels are hidden in a breadboard.
No. It is connected to nothing on the board. It is there so every TinkerBlock block has the same four-pin header and one cable fits all of them. Wiring it does no harm and changes nothing.
Turned over, the order reverses: SIGNAL is on the left and GND on the right, and GND is still the square pad. The back prints TK28 KNOCK SENSOR and SENSES VIBRATIONS instead of the names. Count from the square pad and you cannot get it backwards.
They are where the switch's two legs come through the board and are soldered. One leg is VCC and the other is SIGNAL. Nothing else is wired to them, and there is nothing to connect there yourself.
What holds SIGNAL at 0 V while nothing happens, and what makes the LED flash.
The pull-down and the light →Edit this page — content/books/knock-sensor/the-four-pins.mdx
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