A Charged Cloud Alert Device Project - Or - My Crystal Set Meets Ben Franklin's Kite

Based on knowledge that Ben already had plus what he learned from the kite experiment, he invented the lightning rod. He had observed that strong sparks of electricity jump easily from smooth surfaces such as ball-shaped electrodes, but never do so if at least one of the electrodes has a sharp point. When accumulating a static charge, if there is a sharp pointed electrode, it causes many tiny little harmless discharges rather than the big one we call lightning.

A lightning rod consists of a sharp wire usually at the top of a building that is connected to ground. It drains the electrical charge from air masses that drift by during storms.

A crystal set radio antenna wire located outdoors that is small in diameter (especially an uninsulated one) probably acts very similar to the sharp point at the top of a lightning rod. It tends to provide the same function as long as it presents a DC path to ground. Like most others, whenever I am not using my crystal set, I try to keep the antenna lead connected to the ground lead. This essentially turns my antenna wire into a lightning rod which lowers the odds of lightning striking it or things near it.

Sometimes people install lightning arrestors between their antenna lead-in wire and ground. These arrestors include two sharply pointed electrodes that are close together and pointing at each other. One is connected to the antenna lead and one is connected to ground. If a high voltage begins to appear between the electrodes (that is, between the antenna wire and ground), very small discharges take place between the two points to keep the charge on the antenna from exceeding a safe level. Here can be seen an example of a simple homemade lightning arrestor: http://myplace.frontier.com/~bwalker1945/LongWire4.html Still, the charge might reach upwards of many hundreds of volts or more before this safety device begins to act.

One evening a few weeks ago, we were experiencing pop-up thunderstorms around our part of Ohio. I was playing with my crystal set and noticed just how much crackling static was happening in my earphone. It was being caused by the various storms even though there were no storms within perhaps 10 miles of our house.

My antenna lead terminates in an insulated alligator clip which makes it easy to move from place to place. At one point, I was moving the antenna lead from one tap on a coil to another tap. As the alligator clip reached its new location, I observed a distinct spark between the clip and the tap terminal. Instinctively, I drew the alligator clip away and paused for a moment. I tried again and saw the same spark. I repeated it another time or two. I momentarily wondered whether I had somehow managed to get our house's electrical power tied into my crystal set circuit but, based on my experiences with my CB antenna many years earlier, I soon realized that the whole thing was a side effect of the distant thunderstorms.

Recognizing what was happening, I reached into my parts boxes and pulled out an NE-2 Neon lamp. When a Neon lamp is on, it glows with a characteristic orange color. Typical small Neon lamps contain two electrodes enclosed in a glass envelope which is filled with low pressure Neon gas. The two electrodes connect to the outside world via two wires.

When the lamp is in its resting condition, the two wires behave as if they are an open circuit having a very high leakage resistance of many tens of megohms. However, if the voltage between the two electrodes reaches a critical point (about 90 volts), the Neon gas begins to ionize and conduct electricity between the two electrodes. This is also when it gives off the orange glow. Once on, the lamp will stay lit until the voltage falls below about 60 volts. Then it returns to the off condition.

NE-2 Neon lamps are the most common type available although many others look similar and behave very similarly. They generally resemble this:

When I connected an NE-2 Neon lamp between the antenna and ground leads while charged thunderstorm air masses were drifting past my antenna, I observed the Neon lamp to exhibit a series of dim, fast blinks of orange glow. These rapid dim blinks were rather hard to see, but they were there. Placing something black behind the lamp helped make them visible.

To make the blinks much more distinct, but occur less often, I paralleled a capacitor with the Neon lamp. I needed a capacitor with a maximum voltage rating of at least 200 volts. I chose a 0.1 uF capacitor.

With the capacitor connected, the Neon lamp blinked more brightly. The capacitor absorbs the energy until its charge reaches 90 volts and then the Neon lamp fires to discharge it. How fast the blinking cycle repeated was dependent on how much charge my antenna was receiving from the charged air masses passing by. It stopped completely when the storms had moved on and there were no strongly charged air masses in my area.

By the way, some air masses invoked a positive charge while others invoked a negative charge. The orange glow in a Neon lamp appears around the more negative electrode. Closely observing the lamp can reveal how the polarity changes from time to time during a stormy evening.

As interesting as this circuit is, a Neon lamp just never really blinks very brightly. I found it easy to miss if I was not looking directly at the lamp. I wanted something more striking to take place. My next step was to consider adding a high-brightness LED. It turns out that two LEDs are needed, wired in parallel with one pointing each way because the cicuit needs to handle both positively and negatively charged air masses.

Any color of LEDs could have been used but I selected Blue to indicate when the antenna is experiencing a negative charge and Red when the antenna is experiencing a positive charge. The blink rate remained about the same as before but now the blinks were substantially brighter and much more noticeable. The Neon lamp is still required as it provides the necessary hysteresis between fire (90 volts) and extinguish (60 volts) voltages.

Of course, with all this stuff connected between my antenna and ground, it seemed there would be no way to also use my crystal set radio. <Scratch head for a few minutes.>

Adding a radio frequency choke in the ground circuit keeps all this blinking activity working just as before but also allows all the radio signals (less the high voltage DC charges) to appear directly across the RF choke. The radio signals can still be routed to a crystal set even while this circuit is detecting the charged air masses during times of storm activity. Having arrived at a workable circuit, I abandoned my prototype which was built on an old remnant of lumber and rebuilt it in a plastic project box that had long awaited a project. Here is the schematic and photos of the finished piece ready for use.

Although the Neon lamp is still necessary in the circuit, I decided that I did not need to be able to see it. The LEDs readily catch my eye when they blink.

Just to be clear, the blinking of these LEDs and the Neon lamp are not synchronized with lightning strikes. Indeed, much of the blinking takes place when there are no strikes. Also, having lightning strikes taking place at some distance will not necessarily cause charged air masses to drift past my antenna and cause the LEDs to blink.