Heart rate monitor

  
Light filtering through the finger tip is detected by the cadmium sulphide photoresistor CD1 which forms the feedback network for transducer amplifier section ICA producing a weak signal which is further amplified by ICB. This signal is now compared against a user adjusted threshold, comparator ICD triggers gating on the piezoelectric buzzer PZ1. On each falligg edge of the comparator's output signal one-shot multivibrator ICD produces a 2 ^s pulse which is inverted by Ql and averaged by the RC network consisting of Ml, C6 and C7.

The 10 trimpot R20 in Ql's collector circuit sets the scale factor for Mi where full scale is 150 beats per minute.




Leave Comment

characters left:

New Circuits

.