Build Your Own Lightning Predictor Circuit – 300kHz

Description

Indeed, enjoying VHF FM broadcasts presents considerable benefits compared to MW/LW AM transmissions from earlier times – currently, we experience vibrant stereo sound free from disruptions, signal degradation, and unwanted noise! However, your FM radio will no longer accurately forecast the imminent arrival of a thunderstorm as did the AM radio previously – consistently and with considerable lead time before the adverse weather arrived! The fundamental principle is that AM detection faithfully replicates the characteristics of electrical disturbances such as lightning and large static discharges approaching, in a straightforward manner: these are perceived as subtle crackling sounds in the loudspeaker, largely independent of the radio’s frequency setting! Assuming no AM radio is available presently, a specialized VLF receiver attuned to approximately 300 kHz can accurately identify the sound of an approaching storm!

The uncomplicated receiver depicted here incorporates a loosely-tuned amplifier driving a flashing circuit that illuminates an LED in synchronization with the electrical storms. The frequency and brightness of the LED activity reflect the strength and distance of the approaching storm respectively. Examining the circuit diagram, the LED driver is not activated to flash until a surge of RF energy, amplified by T1, reaches the base of T2. The receiver operates on 3 volts and has a minimal standby current of about 350 microamperes, which will hardly impact the longevity of a pair of 1.5-V D-size cells. T2 and T3 constitute a monostable generator triggered by sudden decreases in T1’s collector voltage.

More about components

Integrated circuits, often referred to as ICs, are complex semiconductor devices containing many interconnected transistors, resistors, and capacitors. In this circuit, the LM339 is a versatile comparator IC commonly employed for detecting voltage thresholds. This IC effectively compares two input voltages, triggering an output signal when one surpasses the other. In this instance, the LM339 acts as the comparator, initiating the LED flashing sequence when the amplified RF signal from T1 exceeds a predefined voltage level. These ICs are known for their compact size, high reliability, and ease of integration, making them ideal for precision circuit designs. They're available in a variety of packages, including DIP and SOIC, and are readily obtainable from numerous electronic component suppliers. The LM339 typically operates within a voltage range of 3V to 16V, making it compatible with the input signal received from the antenna. Its precise comparison capabilities ensure reliable detection of the storm’s intensity through the LED flashing mechanism.

Circuit diagram:

Preset P1 is adjusted until the LED remains off when there’s no thunderstorm nearby for several hundred miles. The value of the LED series resistor is subject to experimentation and LED current. L2, C1 and the antenna are coarsely tuned for resonance at approximately 300 kHz. Frequency-wise, lightning is a fairly broadband phenomenon so any tuning between 200 and 400 kHz will be suitable for the circuit but be certain you’re not inadvertently tuned to a proximate VLF transmitter! The input signal is derived from a 70-cm length of rigid wire, with coil L1 inserted for impedance matching and extending the antenna electrically.

Warning:

This circuit and specifically the antenna must not be utilized to attract lightning. Consequently, neither the circuit nor the antenna may be deployed outdoors and/or powered from the mains supply.