Collision Sensor

What it is

A lever microswitch, a 10 kΩ pull-down resistor, and a red LED that lights while the lever is pushed in. At rest the pull-down holds SIGNAL at 0 V and your board reads LOW. When something pushes the lever in about a millimetre and a half, the switch clicks, connects SIGNAL to VCC, and your board reads HIGH. Let go and it is LOW again.

It is the TK04 push button's circuit with a different switch, and it reads the same way. What it is for is different. Ultrasonic and infrared sensors report a distance, and some surfaces fool them. A bumper reports nothing at all until it touches something, and then it is certain. Use a distance sensor such as the TK50 to slow down for what it can see, and this for what it could not.

VCC is the voltage your pin sees

The switch joins SIGNAL straight to VCC, so whatever is on VCC is what your pin receives on a hit:

Never 5V beside a 3.3 V board, and never a motor battery. With VCC unconnected, the bumper does nothing and the light never comes on. The LED currents are worked out from a red LED's typical forward voltage rather than measured.

Which pin is which

Switch at the top, header at the bottom, reading left to right:

The switch has contacts called COM, NO and NC of its own. The board wires COM to VCC and NO to SIGNAL, and leaves the switch's NC unconnected; the header's NC pin is a different thing that also goes nowhere. The back prints TK17 COLLISION SENSOR and DETECTS IMPACTS instead of pin names. Turned over, the square pad is on the right, and it is still GND.

Wiring, in three lines

1. GND to your board's GND.
2. VCC to 5V on an Uno, 3V3 on an ESP32, ESP32-S3 or Pico.
3. SIGNAL to a digital pin: D2 on an Uno, GPIO 25 on an ESP32, GPIO 4 on an ESP32-S3, GP15 on a Pico.

Leave NC unconnected. Set the pin to INPUT, not INPUT_PULLUP: the pull-down is already on the board. These are the TK04 push button's pins too.

Example

// The GPIO number SIGNAL is wired to.
// Uno: 2. ESP32: 25. ESP32-S3: 4. Pico: 15.
const int BUMPER_PIN = 4;

void setup() {
  Serial.begin(115200);
  pinMode(BUMPER_PIN, INPUT);   // the block has its own pull-down
}

void loop() {
  if (digitalRead(BUMPER_PIN) == HIGH) {   // HIGH is a hit
    Serial.println("hit");
  } else {
    Serial.println("clear");
  }
  delay(200);
}

from machine import Pin
import time

# The GPIO number SIGNAL is wired to. ESP32: 25. ESP32-S3: 4. Pico: 15.
bumper = Pin(4, Pin.IN)       # no pull: the block has its own

while True:
    if bumper.value() == 1:   # 1 is a hit
        print("hit")
    else:
        print("clear")
    time.sleep_ms(200)

Where to start

The handbook below is ten short articles, each with a working figure. The first read is the whole build in three wires and a few lines, and stop and back off is the sketch a robot actually needs.

If your hit counter goes up by more than one per bump, read one bump counts as several and then counting hits.

And before plugging it into an ESP32, VCC sets the voltage is the one page that protects the board.