Question for 204-121ST

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------Question for 204-121ST Please Put your question below------

Please explain the meaning of the schematic diagram shown in the data sheet below.

datasheet
datasheet360×202 25 KB

The schematic diagram from the resources is as follows.

schematic
schematic315×148 2.14 KB

Is it correct to understand that for this to function as an SPDT switch, pins 2-3 are connected and pins 1-4 are not connected when OFF, and pins 1-4 are connected and pins 2-3 are not connected when ON?

2

Hi @haruki ,

Welcome to DigiKey TechForum and thanks for your inquiry.

The DIP switch MPN#204-121ST is a Single Pole Double Throw (SPDT) type, meaning it has:

  • One common terminal (C)
  • Two output terminals (typically labeled 1 and 2)

In the schematic diagram:

  • Pin 1 and Pin 4 form one switch path
  • Pin 2 and Pin 3 form the other switch path

image
image447×304 2.14 KB

Correct Interpretation of ON/OFF States
Your understanding is mostly correct, but let’s clarify it precisely:

When the switch is in the OFF (default) position:

  • Pins 2 and 3 are connected
  • Pins 1 and 4 are not connected

When the switch is in the ON (actuated) position:

  • Pins 1 and 4 are connected
  • Pins 2 and 3 are not connected

This behavior matches a locking SPDT switch, where the toggle or push action changes the connection from one path to the other.

Tip for Testing:
You can verify this with a multimeter in continuity mode:

Test between pins 2 and 3 when the switch is not pressed.
Test between pins 1 and 4 when the switch is pressed or locked ON.

Additional Information:

1 Like
3

Thank you for your response. I understand.