How to Design Micro-Powered LED Flasher

A simple LED flasher can be built with a TLC7555 Timer used as a lowfrequency oscillator and drive to an LED. lC1 runs in a low frequency determined by R?R3 and C1. Frequency is in the range between 0.1 and 5 Hz but

you can alter it by changing Cl. This capacitor can range from 1 to 10 uF.

Duty cycle is determined by R2/R3 ratio and is important in applications where

you need reduction of energy consumed. Though Figure 1 shows fixed resistors for R2 and R3, you can use trimmer potentiometers if you prefer. The

potentiometers, of course, are handy for altering the frequency and duty cycle

of the oscillator.

Rl values depend upon the power supply voltage. With power supplies between 5 and 6 volts, R1 is 470 ohms. With power supplies between 6and 9

volts, Rl is 560 or 680 ohms. With power supplies in the range between 9and

12 volts, Rl must be 1,000 ohms. The circuit drains only 250 uA from a 6-volt

power supply.

Figure lshows the schematic diagram for the Micro-Power LED Flasher. At

the heart of the circuit is lOl, a 555 timer.

Use the parts placement diagram as a guide when assembling the MicroPower LED Flasher. Components placement, using a terminal strip as chassis, is shown in Figure 2.

Take special care with positions of polarized components, such as the LED

and electrolytic capacitor.

After you are sure that you have wired all the components correctly, put the

batteries in the battery holder. The LED should flash.

Parts List - Micro-Power LED Flasher

lC1 - TLC7555 CMOS Integrated Oircuit - Timer

LEDI - Common red, green or yellow LED

D1 - 1N914 general purpose silicon diode

Rl - 560 ohm, 114W,5% resistor

R2 - 1,000,000 ohm, 114W,5% resistor

Rg - 4,700 ohm, 114W,5% resistor

C1 - 4,7 uF,6 IM/DC electrolyticapacitor

C2 - 10 UF, 12 W\/DC electrolyticapacitor

81 - 6 to 12V AA cells, 9V battery or power supply