South African Amateur Radio Development Trust
P O BOX 90438 GARSFONTEIN 0042 SOUTH
OBJECTIVES OF THE TRUST
|UPDATED 31 January 2010||SARL YOUTH BURSARIES|
Amateur Radio Mirror
Mondays 21:05 CAT
Bursaries are available for learners and students under 25 years of age to become radio amateurs. Details
BUILD A LIGHTNING
John Willescroft ZS6EF
A Sunday Afternoon Project that is Interesting to use and can be really useful.
It is a nice summers day and you are enjoying your hobby, then suddenly a thunder clap announces the start of the antenna race. Can you disconnect the HF antennas before the next bang or will you be holding the connector in your hand when the next strike occurs. We have all been there, we try and pull out the plugs before it gets to bad, but sometimes we are caught.
This device called the Lightning Predictor it will give you a warning of an incoming lightning strike and with a little imagination and Amateur ingenuity you can use it to disconnect things before and during a storm.
The device is very simple it measures the static charge between the clouds and the earth and as the charge builds up before a storm the led indicators shows you the charge increasing in intensity. It is very interesting to watch the wave type motion as the led signals increase and decrease, as the static charge increases and decreases, as a storm approaches, and the sudden drop in charge when a strike occurs.
The rod picks up the static charge together with other electronic noises. The resistor which is adjustable makes sure the correct level can be set on the microprocessor pin. The zener diode protects the microprocessor pin from over voltage, and the capacitor slows down the fast edges of the lightning so that the zener can clamp them.
The microprocessor measures the AC & DC voltage components on the input pin to determine when the result is between 4 set levels. When each level occurs the appropriate led is lit. No charge on the pin and the bottom led will flash every second to show you the unit is alive and the microprocessor is working. When the lower led stays alight then a small charge is present. As the charge increases the next led will light and so it carries on increasing until the top led is alight.
When the top led is alight then a strike is immanent, by this time you are checking your rigs for damage.
You will find an option link on the PCB LK1. When this is linked permanently the bottom led will flash each time any led is re-lit. This allows you to disconnect the led and connect a small sounder with a diode across it to the bottom led. This arrangement will give an audible warning when conditions change. The 1 second flash to show the unit is connected and working is removed so when you just hear the beep. All will be quiet until the charge builds up then you will hear the beep and know the fun has started.
The Lightning Predictor is now available in kit form
How to order the kit
Deposit R150 including packaging and postage in the SA Amateur Radio Development Trust account.
Send proof of payment and your full name and delivery address (postal) to email@example.com
Mark the subject line LP order