Lightning Detector Circuit: Build Your Storm Warning Device

Egor! Hurry over! A tempest is approaching!

Here is a VLF receiver set to 300 kHz designed to detect the static of impending thunderstorms. A bright lamp flashes in synchrony with the lightning strikes indicating the proximity and strength of the storm. Figure 1 depicts the straightforward receiver which includes a tuned amplifier powering a modified flasher circuit. The flasher is configured to remain inactive until a surge of RF energy, amplified by the 2N3904, is applied to the base of the 2N4403. The receiver’s idle current is approximately 350 microamps, a negligible amount for a couple of D cells, and hardly diminishes the battery’s lifespan. Naturally, the more severe the weather, the shorter the battery duration.

Circuit Diagram

For optimal effect, position the lamp in a vintage holder featuring a large, colored glass lens. Alternatively, construct your own fixture with a sheet of textured colored glass situated behind a panel painted with black-crackle finish. Explore ideas by viewing several classic science fiction films for inspiration.

A completely different strategy involves mounting the circuit within an empty glass jar, with the antenna and bulb projecting through the top. (A malted-milk jar’s red plastic lid provides easy access and a visually appealing appearance.) Utilize a pin jack for the antenna. The device presents a distinctly handcrafted aesthetic while remaining fascinating.

Boat operators may elect to replace the lamp with a 3-volt buzzer to provide an early warning of deteriorating weather conditions. Select one of those unbreakable clear plastic jars similar to large coffee creamer jars. Apply a small amount of silicone rubber to seal the antenna hole within the jar lid. Employ a longer antenna for enhanced sensitivity, considering the limited electrical noise sources on the lake.

2N3904

The 2N3904 is a small-signal NPN bipolar junction transistor commonly used as a general-purpose amplifier. In this circuit, it acts as the initial gain stage, amplifying the weak RF signal received by the antenna. Its characteristics, including a moderate gain and relatively low saturation voltage, make it suitable for this application. The transistor is essential for boosting the signal strength before it's processed by subsequent stages, ensuring reliable operation of the flasher circuit. It is a common component in many low-power electronic circuits and is known for its ease of use and reliability.

2N4403

The 2N4403 is a general-purpose silicon NPN bipolar junction transistor. Here, it serves as the second amplification stage. Its design allows for a further amplification of the signals received, improving the sensitivity of the detector. The transistor ensures that the signals are suitably strengthened for reliable operation. Due to its robust nature, it is frequently deployed in electronic applications where reliable amplification is required. It is a highly popular choice for beginners due to its simplicity and ease of use.

Calibration is straightforward: adjust the potentiometer until the regular flashing ceases completely. (Utilize a multi-turn trimmer.) When properly calibrated, the lamp will occasionally flash when large motors or appliances switch on and off, and approaching storms will produce a dramatic display. Clearly, calibration becomes more challenging during severe weather. Adjust the potentiometer without the antenna if lightning is nearby. Tune an AM radio to the bottom of the dial to monitor the pulses that the lightning detector is receiving.

This lightning detector is not overly sensitive, so it won’t flash with every radio crackle but will only flash when storms are close. Enhanced sensitivity can be achieved by extending the antenna length, considering the limited electrical noise sources around the lake. The experienced experimenter might add another gain stage after the first by duplicating the 2N3904 circuitry, incorporating a 47-ohm emitter resistor to slightly reduce gain. However, this additional gain can cause instability if the layout is poor; therefore, novices are advised to use a longer antenna or adjust the sensitivity potentiometer with greater care. (When operating correctly, the added gain reduces the need for precise potentiometer adjustment.)