Low Cost LED Blinker circuit


Here is a simple LED
Alternate flasher for decoration purpose. The 20 High bright LEDs
flashes alternately giving a brilliant colour display. The circuit is
low cost and derives DC directly from AC without using a step down
transformer. The design is too simple so that the circuit can be
assembled on a small piece of common PCB.

Power to the circuit is derived from 230 Volt AC through AC capacitor CX
which is used to step down 230 volt AC to low volt AC. 474 K 250 Volt
AC capacitor gives around 20 volts AC and 40 mA current. This low volt
AC is rectified through the Bridge rectifier D1 through D4 and filtered
by C1.

The LED driver is an Astable multivibrator using two
NPN transistors T1 and T2.The circuit works on the principle of
charging and discharging of capacitors C2 and C3. Current from the
positive rail flows through first set of LEDs 1- 10 to the collector of
T1 through resistor R3. Resistor R3 limits current through the LEDs to
protect them.

The current through R3 and LEDs charges capacitor C2. It then
discharges through the base of T2 and resistor R5. This gives base
current to T2 and it conducts. As a result second set of LEDs 11-20
lights. As the Capacitor C2 discharges completely, T2 turns off and LEDs
11-20 also turns off. The same thing happens in the other side also.
This gives alternate flashing of LEDs. Thus the flashing effect is
produced through the switching of T1 and T2 by the charge from
capacitors.

Low cost LED Blinker circuit diagram

Connection: Connect high bright Red LEDs 1-10
serially from R3 to the collector of T1. Similarly connect High bright
Green LEDs 11-20 from R4 to the collector of T2. Cathode of LED 10 and
LED 20 should be connected to the collector of T1 and T2 respectively.
The LEDs can be fitted alternately on the display boards or Photo frames
by drilling holes. Connect the LEDs with the circuit using thin plastic
wires.

Caution: This circuit is dangerous since
it uses high volt AC which can be lethal if handled carelessly. Do not
touch or trouble shoot when the circuit is connected to mains. Do not
try the circuit if you are not an experienced person to handle AC
circuits.

What is LED?


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