Marcus Glahn: Difference between revisions

The basic principle is the translation of of the human blood flow into an electronic value. The photocell changes its resistance up to the light going into it. The resistance changes if fresh blood comes through your fingertip because of the decreasing of passing light. Two 546B transistors (operation amplifiers) switching the LED array on and of. Up to the size of the fingertip the sensitivity of the photocell (resistance) has to be set with a potentiometer. Due to some experiments and experiences i decided to use a combination of a fixed and a variable resistor (the poti). The variable resistance can be changed from 0-470 ohms which allows a fine threshold setting for the fingertip size.