BeginnerLighting
555 LED Flasher
Build an adjustable blinking LED with a classic NE555 timer; learn the timing-capacitor and resistor relationship.
Parts from the database
- NE555P × 1Timer IC
Other supplies
- solderless breadboardCommon build supply
- 5 mm LEDCommon build supply
- 330 Ω resistorCommon build supply
- 10 kΩ resistorCommon build supply
- 100 kΩ potentiometerCommon build supply
- 10 µF electrolytic capacitorCommon build supply
- 100 nF decoupling capacitorCommon build supply
- regulated 5 V supplyCommon build supply
- jumper wiresCommon build supply
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Connections
- Pin 1 to ground; pin 8 to +5 V; pin 4 (RESET) to +5 V.
- Join pins 2 and 6. Connect the timing capacitor from this joined node to ground.
- Connect 10 kΩ from +5 V to pin 7. Connect the 100 kΩ pot as a variable resistor between pin 7 and pins 2/6.
- Put 100 nF across pins 8 and 1. Connect pin 3 to the LED through 330 Ω, with the LED cathode to ground.
Build steps
- Build the power and decoupling connections first, then check the timer chip notch and pin numbering.
- Add the timing network and verify the capacitor polarity before powering up.
- Add the LED and current-limiting resistor. Turn the potentiometer to change the blink rate.
- If you have a multimeter, measure pin 3: it should switch between low and high rather than stay fixed.
Software and firmware setup
This is a hardware-only circuit; no firmware is required.
Test your build
The LED should blink continuously; turning the potentiometer should make it noticeably faster or slower. Approximate frequency is 1.44 / ((RA + 2×RB) × C); real parts and the potentiometer's wiring affect the result.
Troubleshooting
- If the LED stays dark, check its polarity and the pin 3 connection.
- If the output never changes, recheck pins 2, 6 and 7 and make sure RESET is high.
- If timing is erratic, shorten the timing-node wires and check the 100 nF supply bypass.
Safety and limitations
Use a regulated low-voltage supply only. Never connect this breadboard circuit to household mains.
Manufacturer and platform documentation
Community Notes for This Project
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