AC power supply voltage out-of-limit indication circuit

When the power supply voltage is lower than the lower limit value, the yellow light-emitting diode VL2 lights up. When the power supply
voltage exceeds the upper limit, the red LED also lights up (that is, VLi ~ VL3 all light up).
    Adjust the potentiometers RPi and RP2 to change the lower limit and upper limit setting values.
    TP-801 single board computer uses 5v DC power supply. In order to protect the single board computer from the threat of excessive power supply voltage , use