Both these circuits are remarkable in that they can flash an LED from a single 1.5V battery. A typical LED needs 2-3V to work properly and both these circuits include a voltage doubler to boost the voltage to drive the LED. Both circuits will operate continiously for several months on an alkaline AA battery. I have one circuit that is still flashing (ca. 1 second flash rate) after 10 years of continious service on one HP2 Duracell battery !
click on above 'thumb-nails' to get full details of circuit diagrams
The transistor circuit is included because of the recent difficulty in finding a supplier for the LM3909 flasher IC. The designer (Michael Kin, Electronics World, p.483, June 1998) claimed that the transistor circuit should operate for greater lengths of time than the IC circuit. See for yourself in the results below which show the battery voltage and flash rate comparisons for the two circuits left-on for a number of months.
Click here for information about the best LED to use
Bat info: two AA 'Duracell Ultra' bats were used for the test taken from a two AA pack (bats. marked b.b.f MAR 2007).
COMPARISON OF RESULTS FOR THE TWO FLASHER CIRCUITS
|DATE||Transistor bat V||Trans. Flash/min||LM3909 bat V||LM3909 Flash/min||
2 x bright
transistor v dim
LM3909 not flashing
(NOTE: ' - ' means data missing for this entry)
THE CREATIVE SCIENCE CENTRE, 2001
(JPH-NESTA supported project)
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