Pressure sensing system

A pressure sensing system comprising:

• a circuit board having a top surface and a bottom surface;
• a case located near the bottom surface of the circuit board, wherein a distance between circuit board and the case decreases when the circuit board is subjected to a pressure;
• a cover layer covering a part of the top surface and a part of the bottom surface, wherein a part of the top surface which is not covered by the cover layer includes a plurality of first passing zones and a second passing zone, and a part of the bottom surface which is not covered by the cover layer includes a plurality of bottom passing zones;
• a plurality of light emitters located on the first passing zones, respectively;
• and
• a photo detector located on the second passing zone, wherein light emitted by the light emitters enters into the circuit board, and part of the light passes through the second passing zone to enter into the photo detector after being reflected by the cover layer, and part of the light passes through the bottom passing zones to enter into the space between the case and the circuit board.