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Tech Forum

September 2015

Geocache Container With Flashing Light

I’m building a geocache container. To make it look authentic, I’d like the red light to flash every few seconds. Unfortunately, I don’t have any “Nuts & Volts” electronics skills — what type of long-lasting battery and low-power LED light to use — and am hoping to get some expert advice.

Steve Bass
Altadena, CA


Search online for “firefly circuit 7555” and you will find what you want. (Or “unijunction transistor flasher” for the old fashioned method). The LED should be a high brightness type with diffused lens, at least 300mcd. The LED’s above 1CD typically use clear lens, so can’t be seen off axis. As an alternate, if you only need it to run a couple of days, then just solder a L-36BSRD flashing LED inside a 9V battery snap, I make these up for cavers, they leave them behind like breadcrumbs to find their way back.

Bob Turner
Salamander Bay, Australia