A blinking LED circuit can be used for model railroad crossings, blinking bike lights, decorations, or as just a fun introductory electronics project. This circuit uses only one LED, but could be adapted to drive multiple LEDs or blink two LEDs alternately. The circuit uses a 555 timer IC (Integrated Circuit), a very common IC that can be configured to either send a single pulse, or output a square wave oscillating between supply voltage and ground. Here it's used as a type of oscillator called an astable multivibrator.
- Skill level:
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Things you need
- Solderless breadboard
- 9-volt battery clip
- 555 timer IC
- Jumper wires
- 2 10k ohm resistors
- 1uf electrolytic capacitor
- 330 ohm resistor
- 9-volt battery
Place the 555 timer IC on the breadboard so that the pins straddle the centre divider. The 555 IC is an eight pin DIP (Dual In-line Package) chip. There is a dot at one end of the chip. The pins are numbered counter-clockwise from the dot, so if you're holding the chip with the dot at 12 o'clock, pin 1 is immediately to the left of the dot and pin 8 is to the right.
Connect a 9-volt battery connector to the power and ground rails of the breadboard. The red wire on the battery connector is power, and the black wire is ground. Do not connect the battery yet.
Connect pins 4 and 8 of the 555 IC to the power supply rail. Connect pin 7 to the power supply through a 10k ohm resistor.
Connect pin 7 to one leg of another 10k ohm resistor. The other leg of the resistor connects to both pins 2 and 6, and to ground through a 1uf electrolytic capacitor. The negative lead of the capacitor should go to ground.
Connect pin 1 of the 555 IC to ground. Pin 3 is the output pin. Connect one leg of a 330 ohm resistor to pin 3, and the other leg to the anode of the LED. Connect the cathode of the LED to ground. The cathode of the LED is the shorter leg, and sometimes the base of the bulb is flat on the cathode side. Connect the battery, and the LED will blink.
Tips and warnings
- The rate the LED blinks at is controlled by both the value of the capacitor and the values of the resistors connected to pin 7. The duty cycle, or the ratio of when the LED is on to when it is off, is controlled by the ratio of the two resistors connected to pin 7. If they are equal, the LED will be on and off for equal amounts of time. Change both resistor values by the same amount to change the blinking rate while keeping a 50 per cent duty cycle.
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