Blinking LED (Hello, World)
A red light that blinks on and off, all by itself.
What you’ll learn
- What a 555 timer chip does.
- Astable mode — the chip generates its own clock.
- How resistors and a capacitor decide the blink speed.
What you need
| Item✓ | Qty | ~Cost | Where to buy | |
|---|---|---|---|---|
| 9V battery + snap clip | 9V battery + snap clip | 1 | GHS 23.00 | Any supermarket or hardware store. |
| 220 Ω resistor | 220 Ω resistor Look for red-red-brown stripes. | 1 | GHS 0.75 | Electronics shop or online (Amazon, Adafruit). Look for red-red-brown stripes. |
| Red 5 mm LED | Red 5 mm LED Any colour works; red is brightest. | 1 | GHS 1.50 | Electronics shop or online. Any colour works; red is brightest. |
| Half-size breadboard | Half-size breadboard | 1 | GHS 23.00 | Online (Amazon, Adafruit, AliExpress). |
| Jumper wires | Jumper wires | 4 | GHS 30.00 | Online — usually sold in packs of 30. |
| 555 timer IC (NE555 / TLC555) | 555 timer IC (NE555 / TLC555) Bargain even by the bag of 10. | 1 | GHS 7.50 | Electronics shop or online. Bargain even by the bag of 10. |
| 10 kΩ resistor | 10 kΩ resistor Brown-black-orange. | 1 | GHS 0.75 | Electronics shop or online. Brown-black-orange. |
| 100 kΩ resistor | 100 kΩ resistor Brown-black-yellow. | 1 | GHS 0.75 | Electronics shop or online. Brown-black-yellow. |
| 10 µF capacitor (electrolytic) | 10 µF capacitor (electrolytic) | 1 | GHS 1.50 | Electronics shop or online. |
| 100 nF capacitor (ceramic) | 100 nF capacitor (ceramic) | 1 | GHS 0.75 | Electronics shop or online. |
| TotalTotal | ~GHS 89.50 | |||
Build it step by step
Plant the 555 across the trench
Pin 1 at e10, pin 8 at f17 — the chip straddles the centre gap so each side has its own column-strip.
Power pins
Pin 1 (GND) → − rail. Pin 8 (VCC) → + rail.
Tie pins 4 and 8 together
Reset (pin 4) needs to sit at + or the chip won’t run.
Tie pins 2 and 6 together
Trigger and threshold sense the same point on the capacitor.
Drop the timing components
10 kΩ between pin 7 and +; 100 kΩ between pin 7 and pin 6/2; 10 µF between pin 6/2 and −.
Add the bypass cap
100 nF between pin 5 and − keeps the control voltage steady.
Wire the LED
Pin 3 → 220 Ω resistor → LED anode → LED cathode → − rail.
Run it
Snap the 9 V on. The LED blinks at about 1 Hz — once a second.
How it works
The capacitor charges up through the two resistors. When the voltage on it crosses ⅔ of VCC, the 555 flips its output low and starts dumping the capacitor through pin 7. When it drops to ⅓ of VCC, it flips back and starts charging again. The result is a square wave on pin 3 — and a blinking LED. Bigger R or C = slower blink.
If something’s not working
LED stays on (or stays off) and never blinks
- · Pin 4 (reset) is floating — tie it to +.
- · Polarity on the electrolytic cap is wrong.
- · Pins 2 and 6 aren’t connected to each other.
Blinks way too fast or too slow
- · Wrong-value resistor or capacitor. R values stack with C to set the period.
Try this next
Swap the 100 kΩ for a 1 MΩ — the blink slows to a heartbeat.
Swap the 10 µF for a 100 µF — even slower.
Drive a buzzer from pin 3 instead of an LED. You just made a square-wave audio oscillator.