This simple system keeps its battery in a reasonable state of charge for its application - occasional LED lighting. The lighting control system uses a 4W LED lamp, cannibalised from a mains-powered GU10 spotlight whose power circuitry had failed. When the woodshed door is opened a reed relay turns on a 4060 CMOS timer which turns on the light, and then turns it off again when the door is closed or after about six minutes if the door is still open. If light is needed for more than six minutes there is a push-button to reset the timer.
The tricolour LED indicator shines blue to indicate the LED lamp is, or should be, on. Since the indicator LED is mounted outside the woodshed this blue LED indicates if the reed switch fails to turn off the lamp when the door is closed.
These domestic maker circuits are not particularly novel, but they do illustrate some uses of references and op-amps in simple analog control and measurement - and in particular highlight a problem with some types of precision voltage reference, and its solution. And they're real - I've built 'em both in the last couple of months and they are in daily use.
About the author
James Bryant was European Applications Manager for Analog Devices for over a quarter of a century, and is a well-known lecturer on analog electronics. He is the author of many articles, papers and application notes on analog electronics, of many of Analog Devices'Technical Seminars, and of about a third of their monthly"Rarely Asked Questions"columns.
Despite his retirement he still lectures frequently on analog electronics, hypnotism and radio, and is experienced in lecturing in English to audiences whose native language is not English. His website may be found at www.jbryant.eu/home-eng.htm