Hi, welcome to Elonics. In this tutorial, I'll show you how to make a flashing or blinking LED circuit using a 555 time IIC in stable mode. This arrangement toggles the LED on and off at regular intervals of time and the flashing rate can be changed by modifying the value of timing resistor or capacitor used. We'll discuss more about this along with the working explanation later in this video. This circuit is also capable of alternatively flashing two LEDs one after the other by just connecting an extra LED in opposite polarity to the output pin of the 555 IC.
And in most of the LED projects like these, we would like to adjust the LED's flashing duration on the fly and that can be achieved by replacing the timing resistor with a potentiometer. So now we will be able to vary the flashing speed whenever required. Additionally, you might need to add a relay module at the output of 555 timer IC if you intend to use this circuit with heavy loads, for example lights that operate on AC power or LED strips.
For the list of components required, link to the circuit diagram or links to all the previous and upcoming projects, please go through the description below. I will be using this row as positive rail and this as negative rail. Place 555 timer IC on the breadboard with its notch facing up and the pin numbering starts from here. This is pin 1, pin 2 and so on until pin 8. Now connect pin 1 to negative rail and pin 8 to positive rail.
Next connect the pins 6 and 2 to each other and similarly connect pins 4 and 8 of the 555 timer IC to each other. Next, place a 1K ohm resistor between pin 7 and pin 8 of the 555 IC. Then place a 100K ohm resistor between pin 6 and pin 7 of the IC. Next, take a 10uF capacitor and connect its negative terminal to pin 1 of the 555 timer IC and the positive terminal to pin 2 of the IC. Now extend the output pin of 555 IC which is at pin 3. Then connect the anode of an LED to this extended row and the cathode to negative rail via a 220 ohm resistor.
Refer to this table to find out what values of LED series resistor to use, especially if you wish to operate this circuit on 9 or 12 volts. Connect the power supply and the flashing LED circuit is now ready. To increase the flashing rate, you can replace this capacitor or this resistor with a different valued ones. And the pattern is that if you replace this resistor with a smaller valued one, the flashing rate increases and vice versa.
Similarly if you replace the capacitor with a smaller one, the blinking rate increases and the opposite happens when you use a smaller capacitor. For converting this circuit into an alternating 2 LED flasher, you need to connect cathode of another LED to the output pin of 255 timer IC and the R node to positive rail via a series resistor. Here pin 4 is connected to pin 8 which is connected to positive rail, so I've directly connected other terminal of the LED's resistor to pin 4. For dynamically adjusting the flashing or blinking speed, the timing resistor between pin 6 and pin 7 of the 555 timer IC can be replaced with a potentiometer.
So now it is much easy to vary the flashing speed whenever required. Now let's try to briefly understand how this circuit works. If pin 2 detects any voltage less than 1 third of the supply voltage, it turns on the output. And if pin 6 detects any voltage more than 2 thirds of the supply voltage, it turns off the output. And whenever the output is in OFF state, pin 7 will be internally connected to 0 volts.
In this circuit, immediately after the power supply is turned on, the capacitor will be in discharged state and so the voltage at pin 2 will be 0 volts. Since this voltage is less than 1 third of the supply voltage, the output turns on. Simultaneously, pin 7 will internally disconnect from 0 volts and so the capacitor starts charging via resistors R1 and R2.
Once the voltage across the capacitor crosses 2 thirds of the supply pin 6 senses it and turns off the output. Simultaneously, pin 7 will reconnect internally to 0 volts, which results in capacitor discharging via resistor R1. And once the voltage across the capacitor falls below 1 third of the supply voltage, pin 2 will turn on the output and this whole cycle repeats again and again.
You can practically observe the charging and discharging of the capacitor by measuring the voltage across it using a multimeter. And since the resistor R1 is involved in both charging and discharging of the capacitor, increasing its value reduces the flashing rate. This is because the capacitor takes more time to charge and discharge as we keep increasing the value of this resistor.
Similarly, more the capacitor value, more will be the time taken for it to charge and discharge and so the flashing rate reduces. You can use this formula for calculating the resistor or capacitor values for any time period or flashing rate required. Thanks for watching this video, do subscribe and have fun.