Tier 2 · Timer MagicmediumAge 10+40 min
Adjustable Blink Speed
Turn a knob to make the LED blink fast or slow.
What you’ll learn
- A potentiometer is a knob-style variable resistor.
- How an analog input changes a circuit’s timing.
- Why every guitar volume knob is a potentiometer.
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. |
| 100 kΩ potentiometer | 100 kΩ potentiometer Linear-taper (B100K) is fine for this. | 1 | GHS 15.00 | Online. Linear-taper (B100K) is fine for this. |
| TotalTotal | ~GHS 104.50 | |||
Build it step by step
Build Project 6 first
You need the 555 astable working at ~1 Hz before you mod it.
Replace R2 (100 kΩ)
Remove the fixed timing resistor between pins 7 and 6.
Drop the potentiometer in its place
Tie pin 7 to one outer leg, the wiper (middle leg) to pin 6. The third outer leg is unused.
Spin the knob
Clockwise = more resistance = slower blink. Anticlockwise = less resistance = faster.
How it works
A pot is just a fixed resistor with a sliding contact. Wiring it as a "rheostat" (two legs, ignoring the third) gives you a knob-controlled resistance from ~0 Ω to 100 kΩ. In the 555 astable, that resistor sets the discharge time, so the blink rate slides smoothly under your fingers.
If something’s not working
Knob does nothing
- · You wired both outer legs — that’s using the pot as a divider, not a rheostat. Move one wire to the wiper.
Blink stops at one end of the rotation
- · Pot resistance is hitting near zero — the cap charges instantly. Add a 1 kΩ in series so the minimum stays sane.
Try this next
Add a second pot in series — coarse and fine speed knobs.
Swap the LED for a buzzer — adjustable-pitch tone generator.