TTP223 Capacitive Touch Lamp
A copper pad behind plastic, one IC, and a MOSFET — touch anywhere on the surface to toggle a string of LEDs.
Difficulty: Breadboard. Estimated build time: about 30 minutes. Estimated parts cost: about US$4.60. 5-line bill of materials. Compare supplier offers when available. A touch-activated lamp that uses no buttons or switches — just a pad of copper foil hidden behind a plastic enclosure.
Decide the mode
Look at the TTP223 breakout's back: there are two small solder pads labeled A and B. Both unsoldered = momentary output (high while touched). Bridge A = toggle mode (each touch flips). Bridge B = active-low. We want toggle, so bridge A with a tiny solder blob.
Make a touch pad
Cut a 25 mm × 25 mm square of adhesive copper foil and stick it to a piece of plastic. Solder a wire to the foil. The foil and the wire are now your sensing electrode — they connect to the TTP223's TPAD pin (or via the breakout's onboard PCB pad if your breakout already has one).
Wire the IC
VCC → +3.3 V or +5 V (TTP223 is happy with either). GND → ground. SIG (output) → 2N7000 gate. The breakout has its own decoupling cap on board; if you're using the bare SOT23-6 IC, add 100 nF at the supply pin.
Wire the MOSFET output stage
9 V battery + → 220 Ω → 3 LEDs in series → 2N7000 drain. 2N7000 source → battery −. Gate → TTP223 SIG (with a 100 kΩ pull-down to ground for safety — keeps the gate from floating when the IC is disconnected).
Calibrate the sensitivity
Power up. Hover your finger near the foil — the LEDs should toggle on. The TTP223 auto-calibrates over ~500 ms when first powered: keep your finger AWAY during the first half-second after power-up. If it's too sensitive (false trips when you bring your hand within 5 cm), put the foil behind thicker plastic. Too dead (have to mash your finger on it)? Use thinner plastic or a bigger pad.