The four pins
Four pins, and three of them are wired to one part: a 10 kΩ thumbwheel potentiometer that stands past the board's top edge. GND and VCC are the two ends of its track, SIGNAL is the contact that slides along it, and NC is connected to nothing.
What is on the board
One part. A thumbwheel potentiometer, 16 mm across and 2 mm thick, lying flat with its face up, 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 rather than down through it, and the board lies flat when it is plugged into a breadboard or a cable.
A potentiometer, pot for short, is a resistor with a third contact that slides along it. This one's track is 10 kΩ from end to end. Turning the wheel moves the sliding contact, which is called the wiper.
The four names
GND is on the square pad, and it is one end of the track.
VCC is the other end. Whatever voltage you put on it is the top of the range: with the wheel at that stop, SIGNAL is VCC.
NC means not connected, and on this board it means it literally. The net list, which is the list of every electrical connection on the board, does not mention it at all.
SIGNAL is the wiper. It carries a voltage anywhere between 0 V and VCC, so it goes to an analog input: a pin that can measure a voltage, not only tell HIGH from LOW.
The wheel stands past the edge
The wheel's centre is about 4 mm below the board's top edge and its radius is 8 mm, so about 3.9 mm of it stands past the edge. That is the part you turn. Because it lies flat, nothing on the board stands up the way a knob on a shaft does, which is the reason to pick this block over the TK08.
The back of the board
Turned over, the order reverses. The square pad is on the right now, and it is still GND. The back is where the part number is printed, TK07, which is the number on the box and the address of this block's page.
When it does not work
Hold the board with the wheel facing you 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 board is in a breadboard and the labels are hidden.
No. It is not connected to anything on the board, on either side. It is there so every TinkerBlock block has the same four-pin header and the same 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 TK07 DISC POTENTIOMETER and a line about what it does instead of the names. Count from the square pad and you cannot get it backwards.
So a thumb can turn it from the side. The wheel lies flat, face up, and about 3.9 mm of it stands past the top edge. In a box or a case, that edge is the one to leave open.
What the wheel does to the voltage on SIGNAL, and the current that does not change.
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