It’s the circuit of dancing light using 555 Timer constructed in astable mode. This circuit blinks two LEDs randomly with a small delay and it can be easily modified to include more LEDs or for controlling incandescent lamps. Time period of oscillation is dependingon the value of R1, R2 & C1.
1st and 8th pins of 555 Timer are used to provide power, Vcc and GND respectively. 4th is the Reset pin which is active low input and is tide to Vcc to avoid accidental resets. 5th is the Control Voltage pin which is not used in this application, hence it is grounded via 0.01μF capacitor to avoid high frequency noises. When the output is HIGH capacitor charges to Vcc via resistor R1 and Diode. When the output is LOW capacitor discharges via resistor R2 and Discharge pin (7th) of 555 Timer.
When the output is LOW (0V) upper LED glows and when the output is HIGH (5v) lower LED glows. Instead of current limiting resistors R3, R4 you may use another LED, such that two LEDs will come in series. You can use higher supply voltages if you need to drive more LEDs. 555 can source or sink up to 200mA current, if you need more current use a transistor driver.
You can also connect this circuit to relay for controlling incandescent lamps as shown below.
Here transistor is wired as a switch, when the base input is HIGH transistor turns ON and the relay is energized. Since the output of the 555 timer is square wave, the relay energizes and de-energizes continuously. Incandescent lamps turn ON alternatively since they are connected to Normally Open (NO) and Normally Closed (NC) of the relay output.
555 Timer IC
Resistors R1 = R2 = 100k, R3 = R4 = 330 or 470 ohm
Capacitors C1 = 10uf (106) microfarad and C2 = 0.01uf (103) microfarad
Components for relay circuit
12V DC battery or supply
12volt DC relay
Resistor - 4.7k