Reaction tester electronic project circuit

A very simple reaction tester can be made using electronic scheme in the figure below. when the power button Contact is closed, astabil multivibrator built around IC1 produces pulses which are applied to counter IC3. As soon as S2 button was actuated, astabil multivibrator circuit is blocked, the latest LED lights in order to further decoder IC4. Frequency of the astabil multivibrator can be adjusted using potentiometer P1 between 10 and 80 Hz. The circuit requires a supply voltage of 5 volts and a maximum current of about 120mA.