But I didn't want to rip off someone elses stuff and the design constraints I had put in place were pretty tight so I started from scratch...
Detecting lightning requires 'listening' for the RF energy produced during a thunder storm. Any AM radio can detect this, so build an AM radio, connect it to something that will register the loud pops and crackles from the lightning and your done.
Display
I decided the display power requirements were 2V to 5V at no more than 500uA. I wanted an LED display that would show how often the lightning was occurring.
LED's are realy efficient now and putting 250uA through some white ones I had on my desk gave a satisfactory light output. The LED's would need multiplexing since I could only light them one at once. Again going with what was at hand I used a PIC16LF819, which when clocked at 31kHz only draws about 7uA.
Radio
I wanted a simple AM radio front end that would use a ferrite bar antenna so it would fit nicely in a box. I have collected hundreds of circuit ideas that would suffice so I tried out one I had on a scrap of paper...
This worked quite well but then I got obsessed with building an AM radio that tuned the LW and MW bands. The radio I needed would tune to somewhere below 500kHz, peak detect the received signal and buffer it for sampling by the PIC. The test circuit is shown below, its a simple reflex receiver followed by an amplifier and peak detector. It uses a moving coil meter as the display.
The coil is a LW radio coil wound on a 12cm ferrite rod. The meter is a 1mA FSD moving coil meter. The detector draws under 500uA from a 5V supply.
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