Monday, July 8, 2013

Portable Lightning Detector

This is not directly Ham Radio Related, but Radio theory does apply. Some of my hobbies include Photography and Storm Chasing. I chase storms from a safe distance, and capture lightning as seen in this picture. While chasing storms, I use the AM radio in my car, tuned to the lower part of the band where it is quiet. I can hear the interference generated by the lightning strikes through the AM radio as it is susceptible to the wide band low frequency pulse from the lightning. This method helps to give me an indication of how active the storms are. The Pops I hear on the AM radio are generated by both Cloud-To-Cloud and Cloud-To-Ground strikes, so this can be useful in determining if charges are still building within the storms nearby. One problem with the AM radio, it hears the lightning strikes from a good distance away, but it doesn't give me any direction information.
With this in mind, I began researching a lightning detector that would react to the same low frequency pulse. I found a few diagrams online that would listen to the AM burst around 300KHz generated by the lighting. I ordered a bunch of parts, and spares, to build a Directional Lightning Detector. After I built the Directional unit, I used the spare parts to make a Portable Lightning Detector.

When a pulse is detected, the red LED will illuminate for about a half second. I added a low voltage vibration motor to this unit so I could have it on my side, and be alerted to lightning in the area. This type of vibration motor can be found in old pagers and cell phones. I plan on adding a 75db 3v buzzer to this design, so I can switch between an audible or a silent alert.
Here is the inside of my Portable Lightning Detector. The unit operates from 2 AA batteries. The White switch is for power, and the silver switch is for which alert, audible or vibrate.

I was going to use the small speaker in this picture, but I am opting for the buzzer instead.
I used a 2m/440 Amateur Radio Antenna for this setup, onto the SMA jack I mounted onto the case. Sensitivity can be improved with a longer antenna if needed. This size of antenna should make this unit sensitive for what I need, while keeping the length to a manageable size.

Current draw while on standby is about 5mA. When the vibrate motor starts, the draw spikes to about 50mA. Based on 2500ma AA batteries, I estimate a runtime of about 300 hours or 12.5 days of standby time.

Below is the schematic diagram of how this Lightning Detector is currently put together.