A peak level indicator when signal exceeds a certain maximum value. This can be very useful, for example, with tape recorders, mixing consoles, etc. One of the most important requirement of a peak level indicator is that it must respond to very brief signals. This circuit is constructed by using an inverting Schmitt trigger 74HC14 CMOS type. Input impedance is high enough peak indicators. Value up to certain limits depending on the position of TR1. Function units as follows. Input half wave rectified by D1. When the voltage exceeds R1 trigger the threshold, a logic [H] generated on the output of the second Schmitt trigger. Trigger threshold dependent on supply voltage. With a 5V supply the trigger level 3.6V. Positive pulse at the output of the second trigger is feedback to the input through C2. The following is a schematic drawing:
If the input signal is very short, the logic level will be maintained during the H charging time C2. This time is determined by the values of C2 and R1. Outputs during this time of the third trigger is the logic of L, so that D4 LED lights as an indication that the input signal level is too high. TR1 trimmer is adjusted to a desired level of maximum peak of the indicator should begin to function.
C1=100nF 100V MKT
C2=150nF 100V MKT
D4=RED LED DIODE