Here is a circuit that can sense the static electricity level in the atmosphere. It gives LED indications for both positive and negative atmosphere charges. The circuit uses a low noise JFET input Opamp TLO 71 to detect the atmospheric charge.
The op amp has well matched high voltage JFET input device for low input offset voltage. The BIFET technology provides wide bandwidth and fast slew rate with two input bias currents. IC1 (TLO71) is designed as a voltage sensor cum signal amplifier. Its Non INV input is connected to the aerial (1 meter plastic wire) through R2. R1 maintains the input impedance of IC1 to make the input sensitivity normal.
VR1 and VR2 adjust the voltage level at the INV input of IC1. Resistor R3 and R4 determines the gain of the inverting amplifier and with the shown values it is 1000. That is, a difference of 1 milli volt at the input gives 1 volt output. Output from IC1 is used to switch on T1 and T2 at different output states.
When there is positive charge in the atmosphere, output of IC1 becomes high and T1 conducts to light Red LED. If the atmospheric charge is negative, output of IC1 remains low and T1 off. This causes T2 to conduct and Green LED lights. These states of LEDs change as the atmospheric charge changes. Adjust VR1 and VR2 for IC’s input sensitivity and VR3 for the threshold level of T1.Adjustments should be done in a sunny day so that atmospheric charge will be around 100 milli volts.