I found this circuit on a December 1976 Radio Elettronica. The Italian magazine no longer exists, but with the replacement of some components the circuit can be easily assembled. For example, we replaced BC107 with BC547, BC548 or BC549. The sensor consists of a small light bulb and an LDR in a tube where we stick our finger. In this way the light goes through the finger, changing intensity according to the pulsations and thereby activating the LED. Outputs A and B can be connected to an amplifier.
