Don't Ride Route 13

Step On It. It Lights Up. That's It.

No soldering. No wiring diagrams. If you can tape two things together, you can make this.

What You Need

• 1 pressure sensor — use any of these: a pressure mat switch (the flat kind from door chimes, under $2), a thin-film pressure sensor (RP-S40-ST, under $3), or make your own from two sheets of aluminum foil separated by a piece of foam with a hole in the center.
• 1 orange LED, diffused (the soft kind, not the bright clear ones. Craft store or online. About a quarter.)
• 1 CR2032 coin battery (the flat silver one from the drugstore) #1 Swamp Glow#2 Route 13
• Electrical tape #1 Swamp Glow#2 Route 13#3 Three-Knock

Parts — where to buy each one →

How to Build It

The pressure mat has two wires. The LED has two legs — one long (positive), one short (negative). Wire the mat in series with the LED and the battery. Long LED leg to battery positive (+). Short LED leg to one mat wire. Other mat wire to battery negative (−). Wrap the connections with electrical tape.

Slide the mat under a chair cushion, a doormat, a rug — anywhere someone will step or sit. Run the LED wire to wherever you want the glow to appear. When weight hits the mat, the circuit closes and the LED lights up orange. Lift the weight, it goes dark.

If you use the RP-S40-ST thin-film sensor instead of a mat, it works the same way — wire it in series. The difference: the harder someone presses, the brighter the LED glows. Light step, dim glow. Heavy step, bright glow.

ATtiny85. Sit Down. Watch It Fade.

A thin-film pressure sensor, same LED — but now a tiny chip reads the pressure and controls the fade. Someone sits, it glows. They stand up, it fades over five seconds. Like the warmth leaving a seat.

Parts

• 1 ATtiny85 chip (8-pin DIP) #1 Swamp Glow#2 Route 13#3 Three-Knock
• 1 thin-film pressure sensor (RP-S40-ST — a flat resistive strip that changes resistance when pressed)
• 1 orange LED (same as Version 1)
• 1 resistor, 150Ω (for the LED) #1 Swamp Glow#2 Route 13
• 1 resistor, 10kΩ (pull-down for the sensor)
• 1 CR2032 coin battery (same as Version 1) #1 Swamp Glow#2 Route 13
• 1 CR2032 battery holder with leads and switch #1 Swamp Glow#2 Route 13#3 Three-Knock

Parts — where to buy each one →

Pin Orientation

Hold the chip so the small notch or dot faces left.

Bottom-left is Pin 1. Top-left is Pin 8. Pins count counter-clockwise.

Pin Reference

• Pin 1 — RESET (leave unconnected)
• Pin 2 — PB3
• Pin 3 — PB4
• Pin 4 — GND (ground)
• Pin 5 — PB0 ← LED output
• Pin 6 — PB1
• Pin 7 — PB2 / ADC1 ← pressure sensor input (analog)
• Pin 8 — VCC (+3V power)

Step 1 — Program the Chip

Use a Tiny AVR Programmer board (~$10) — plug the ATtiny85 into the socket, plug the board into USB, and upload a short program from the Arduino IDE. Six lines. One time. After that, the chip remembers.

void setup() { pinMode(0, OUTPUT); }
void loop() {
  if (analogRead(1) > 100) {       // pressure detected
    for (int i = 255; i >= 0; i--) {
      analogWrite(0, i);           // fade from bright to dark
      delay(20);                   // ~5 seconds total
    }
  }
}

Step 2 — Connect It

Five connections. No soldering. Bend the resistor legs and LED legs directly onto the chip pins — they're long enough.

• Pin 5 (PB0) → either leg of the 150Ω resistor (it works both ways) → other resistor leg to LED long leg (+).
• Pin 7 (PB2) → one wire from the pressure sensor. Other sensor wire to Pin 8 (VCC).
• Pin 7 (PB2) → also connect a 10kΩ resistor from Pin 7 to Pin 4 (GND). This is the pull-down.
• Pin 8 (VCC) → red wire from battery holder.
• Pin 4 (GND) → black wire from battery holder and LED short leg.

Tape it together with electrical tape. The battery holder has a built-in on/off switch.

Step 3 — Hide It

Tuck the circuit behind furniture, under a shelf, or inside a gap. Run the sensor wire to wherever you're hiding it — under a cushion, doormat, or rug. The sensor is thin enough to disappear under fabric.

Troubleshooting

Doesn't light? Check LED polarity (long leg to resistor side). Check 150Ω resistor is between pin 5 and the LED, not bypassed. Check sensor wires are on pin 7 and pin 8 (VCC). Check 10kΩ pull-down is between pin 7 and pin 4 (GND). Check battery is seated. Try flipping the LED. If it triggers too easily, raise the threshold in code (e.g. 200 instead of 100). If it won't trigger, lower it (e.g. 50).