Touch Lamp
Touch a wire and the light stays on for 5 seconds, then turns off.
What you’ll learn
- Monostable mode — the 555 fires once per trigger, then resets.
- Why a tiny static touch is enough to start a circuit.
- How RC values set the on-duration.
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. |
| 470 kΩ resistor | 470 kΩ resistor | 1 | GHS 0.75 | Online. |
| 10 µF capacitor (you may already have one) | 10 µF capacitor (you may already have one) | 1 | GHS 1.50 | Online. |
| TotalTotal | ~GHS 91.75 | |||
Build it step by step
Place the 555
Same straddle position as Project 6.
Wire monostable timing
Pin 7 → + via 470 kΩ; pins 6 and 7 joined; pin 6 → − via 10 µF.
Pull pin 2 high
Pin 2 → + via 100 kΩ. That’s the resting state.
Run a touch wire from pin 2
A bare jumper poking up from pin 2. Brushing it briefly pulls pin 2 low and triggers the timer.
LED on the output
Pin 3 → 220 Ω → LED → −. Touch the wire — the LED stays on for ~5 seconds, then turns off on its own.
How it works
In monostable mode, pin 2 going low for a moment kicks the 555 into its "on" state. The output stays high while the capacitor charges through the 470 kΩ. When the cap reaches ⅔ VCC, the chip flips back. T = 1.1 × R × C — about 5 seconds with these parts.
If something’s not working
Stays on forever after one touch
- · Pin 2 is shorted to −, or the trigger wire is touching another wire.
Doesn’t fire when touched
- · Pin 2’s pull-up resistor is missing.
- · You’re standing on a fluffy carpet — try grounding yourself first.
Try this next
Swap 470 kΩ for 1 MΩ — on-time goes up to ~10 seconds.
Drive a relay from pin 3 — touch the wire, lamp on, watch the relay click.