> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/wokwi/wokwi-docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Relay Module

> Electrically operated switch with normally open and normally closed contacts

Electrically operated switch.

## Pins

<ParamField path="VCC" type="power">
  Supply voltage
</ParamField>

<ParamField path="GND" type="ground">
  Ground
</ParamField>

<ParamField path="IN" type="input">
  Control signal (e.g. from micro-controller)
</ParamField>

<ParamField path="NC" type="contact">
  Normally closed
</ParamField>

<ParamField path="COM" type="contact">
  Common pin
</ParamField>

<ParamField path="NO" type="contact">
  Normally open
</ParamField>

## Attributes

<ParamField path="transistor" type="string" default="npn">
  "npn" (active-high) or "pnp" (active-low)
</ParamField>

## Operation

The relay is an electronic switch.

When the `IN` pin is high / disconnected, `COM` is connected to `NC` (NC means normally closed).

When the `IN` pin is low, `COM` is connected to `NO` (NO means normally open).

Setting the "transistor" attribute to "pnp" inverts the logic: when `IN` is high, `COM` is connected to `NO`, and when `IN` is low / disconnected, `COM` is connected to `NC`.

## Simulator Examples

* [One relay module controlling two LEDs](https://wokwi.com/projects/347308007359513172)
* [Arduino Uno controlling four relay modules](https://wokwi.com/projects/398166790321189889)