Use the advantage of photoplethysmogram（PPG）

an IR optolelctronic muscle contraction sensor circuit in reflection mode is designed.An IR LED driven by a programmable current source emits into muscle tissue.The IR light transmits in a “banana shape” path and finally scatters out of the skin.The output light intensity is relevant to the contraction degree of the muscle.The optolelctronic detection circuit transform the tiny outgoing light signal into electrical signal

after subsequent filtering and amplification processing

AD sampling is carried out by microcontroller unit（MCU）.The result shows that each parameter of the circuit is as expected.The circuit is used to detect isometric contraction of biceps brachii.By measurement and analysis on two arm postures

the output signal can reflect the contraction degree of the muscle.