SC7301 Micro Limit Switch with Lever - 3-Pin SPDT 5A 250VAC

Wiring & getting started

Wiring diagramArduino Nano

1. Find the pins

   Hold the switch with the numbered face towards you, the lever pivot on the left and the tabs pointing down. The tabs read 1, 3, 2 from left to right: pin 1 (COM) at the pivot end, pin 3 (NO) in the middle and pin 2 (NC) at the far end. The back face has no numbers, so check you have the numbered face. At rest COM is joined to NC, and pressing the lever swaps it to NO.

2. Solder two wires

   Hook a stripped wire end through the hole in tab 1 and tab 3, then solder each one. Thin 26 AWG hook-up wire suits a run to a board. Leave tab 2 bare for this test.

3. Connect it to your board

   Wire pin 1 (COM) to GND and pin 3 (NO) to D2, as in the drawing. No resistor is needed, because the example code switches on one built into the Nano. On an ESP32 or Pico, use GND and any free input pin and change the pin number in the code.

4. Load the test code

   Upload this sketch, then open the Serial Monitor at 9600 baud.

   Example Arduino codeArduino C++

   // SC7301 limit switch test for an Arduino Nano or Uno.
   // Wire pin 1 (COM) to GND and pin 3 (NO, the middle tab) to D2.
   const int SWITCH_PIN = 2;
   int lastState = HIGH;
   
   void setup() {
     pinMode(SWITCH_PIN, INPUT_PULLUP);  // turns on the Nano's built-in resistor
     Serial.begin(9600);
     Serial.println("Press the lever");
   }
   
   void loop() {
     int state = digitalRead(SWITCH_PIN);
     if (state != lastState) {
       Serial.println(state == LOW ? "Pressed" : "Released");
       lastState = state;
       delay(20);  // skip the few milliseconds of contact bounce
     }
   }

5. Check it works

   Press the lever by hand. You hear a click and the Serial Monitor shows Pressed, then Released when you let go. If it shows Pressed while the lever is at rest, the wire is on pin 2 (NC): move it to pin 3.

6. Mount it at the end of travel

   Fix it with two M2 screws so the moving part presses the lever near its tip just before the end of travel, with a little travel left after the click. Put a solid stop behind it so the switch only senses the position and never takes the knock.