BeginnerTimers & Logic
555 One-Shot LED Timer
Press a button to start one adjustable LED pulse, then estimate its duration from the timing resistor and capacitor.
Parts from the database
- NE555P × 1Monostable timer
Other supplies
- breadboardCommon build supply
- regulated 5 V supplyCommon build supply
- pushbuttonCommon build supply
- 10 kΩ pull-upCommon build supply
- 100 kΩ timing resistorCommon build supply
- 100 µF electrolyticCommon build supply
- 10 nF capacitorCommon build supply
- LEDCommon build supply
- 330 Ω resistorCommon build supply
- 100 nF bypass capacitorCommon build supply
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Connections
- DIP-8 pin 1 to ground, pin 8 and pin 4 to +5 V; put 100 nF between pins 8 and 1.
- Join pins 6 and 7; use 100 kΩ from +5 V to that node and 100 µF from the node to ground, positive at the node.
- Pull pin 2 up to +5 V through 10 kΩ and use a button from pin 2 to ground. Put 10 nF from pin 5 to ground.
- Connect pin 3 through 330 Ω to the LED anode and its cathode to ground.
Build steps
- Check the IC notch and capacitor polarity before powering.
- Press and release the trigger button briefly.
- The nominal pulse is 1.1×R×C, about 11 seconds for 100 kΩ and 100 µF; real electrolytics have wide tolerance.
- Change one timing value at a time and compare the measured interval.
Software and firmware setup
This is a hardware-only circuit; no firmware is required.
Test your build
One short button press turns the LED on for one delay, then off. Holding the trigger low can retrigger it.
Troubleshooting
- No pulse: pin 2 should be high idle and go low only while pressed.
- LED stays on: check pins 6/7 are joined and capacitor polarity.
- Timing differs: measure the actual R and C; electrolytic tolerance is substantial.
Safety and limitations
Use isolated regulated 5 V only. The output is for an LED or logic input, not mains wiring or a high-current load.
Manufacturer and platform documentation
Community Notes for This Project
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