The invention relates to an improved circuit device of an
infrared photoelectronic switch, which is used for detecting the key action and playing force of a keyboard
musical instrument. The circuit device is characterized in that: two identical phototriode chips manufactured on the same
electrode support are packaged into an integrity to be an
infrared double-control photo
diode by plastic resin, the
infrared double-control photo
diode and an infrared emitting
diode form an infrared double-control photoelectronic switch; each key corresponds to a group of infrared double-control photoelectronic switches and an
auxiliary circuit, the keys, the infrared double-control photoelectronic switches and the
auxiliary circuit are mutually in
electrical connection according to line and row relation to form the matrix scanning circuit of the whole keyboard; and the underside of each key is provided with an infrared
photoresist plate, the two phototriodes arranged in the infrared double-control photo diode are
cut off or conducted in sequence when the
photoresist plate moves up and down along with the key, and a corresponding
signal is output to the master control board of an electronic
musical instrument after being detected by the matrix scanning circuit. The time interval of the signals output when the two phototriodes are
cut off in sequence is detected to calculate the force of playing the keys. Compared with the prior art, the invention has reliability and accuracy, sensitive response, small volume, relatively low cost and strong practicability, and particularly does not influence the playing handfeel of the keys.