Use solar power to charge your 2·4V or 3·4V NiCad and nickel metal hydride mobile phone batteries

Some people shun traditional sun-and-sand holidays to seek the independent life. Carrying a small tent and a minimum of equipment on their back they walk, climb, camp, and fish to get as close to nature as they can. So what self-respecting independent traveler would carry a mobile phone? Apparently, many do. Some simply wish to maintain contact with family and friends at home. Others see it as an important piece of safety equipment that may be used to summon help in an emergency.

However, there is a problem. Once the phone battery has run "flat", it may be impossible to charge it. With no mains or 12V (car) supply available, use of the phone may be restricted to emergency use only and kept switched off most of the time. Even so, the battery (depending on type) will self-discharge fairly quickly. On a long trip, it may be found that it has discharged whether the phone has been used or not.

This solar-operated circuit will charge a nominal 2·4V or 3·6V nickel-cadmium or nickel-metal-hydride mobile phone battery. It may also be used to power an inexpensive 3V personal cassette player (the type that normally use two AA-size cells).