TWO LOW POWER LED FLASHERS

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 lab temp.
(C)
comments
23/07/00 1.61 16 1.61 22 20 -
10/08/00 1.51 - 1.50 - - -
22/08/00 1.49 - 1.48 - - -
28/08/00 1.48 16 1.47 20 - -
01/10/00 1.45 16 1.44 19 - -
28/10/00 1.43 16 1.40 19 - -
06/01/01 1.37 15 1.34 17 10 -
11/02/01 1.35 15 1.33 16 14 -
05/03/01 1.34 15 1.31 16 17 -
05/04/01 1.33 15 1.29 15 - -
05/05/01 1.31 15 1.25 15 - -
05/06/01 1.30 16 1.20 14 25 -
02/07/01 1.27 16 1.18 15 23 -
20/08/01 1.20 15 1.12 12 25 LM3909 brighter
16/09/01 1.20 14 1.07 10 20 LM3909
2 x bright
26/10/01 1.15 14 0.99 8 17 both dim
16/11/01 1.13 13 0.98 7 18 both dim
LM3909 brighter
16/12/01 1.10 11 0.97 not flashing 10 transistor v dim
LM3909 not flashing

(NOTE: ' - ' means data missing for this entry)

THE CREATIVE SCIENCE CENTRE, 2001
(JPH-NESTA supported project)


THE CREATIVE SCIENCE CENTRE

Dr Jonathan Hare, The University of Sussex
Brighton, East Sussex. BN1 9QJ.

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