node-red-contrib-sr-latch

A Node-RED SR Latch (Set-Reset Flip-Flop) node - a memory element that holds its state until set or reset.

Features

• Set state to ON (true)
• Reset state to OFF (false)
• Toggle between states
• Multiple input formats supported
• Topic takes priority over payload
• Configurable output mode (on change only / always)
• Configurable initial state

How It Works

SET    ──┐     ┌── RESET
         │     │
State: ──┴─────┴──────────────
         ON    OFF

The latch remembers its state until changed.

Configuration

| Property | Description | Options | |----------|-------------|---------| | Initial State | State when Node-RED starts | SET (ON) / RESET (OFF) | | Output Mode | When to send output | On state change only / On every input |

Usage

Input

The node accepts multiple input formats:

Via msg.topic (takes priority):

• set or s - Set to ON
• reset or r - Reset to OFF
• toggle or t - Toggle state

Via msg.payload:

• Boolean: true = SET, false = RESET
• Number: 1 = SET, 0 = RESET
• String: "set", "s", "on", "true", "1" = SET
• String: "reset", "r", "off", "false", "0" = RESET
• String: "toggle", "t" = TOGGLE

Output

{
  "payload": true,
  "action": "set",
  "previousState": false
}

| Property | Description | |----------|-------------| | payload | Current state: true (ON) or false (OFF) | | action | Action performed: "set", "reset", or "toggle" | | previousState | State before the action |

Examples

Basic Set/Reset

Input: {topic: "set"}   → Output: {payload: true, action: "set"}
Input: {topic: "set"}   → (no output - already set, no change)
Input: {topic: "reset"} → Output: {payload: false, action: "reset"}

Using Boolean Payload

Input: {payload: true}  → SET (ON)
Input: {payload: false} → RESET (OFF)

Toggle Mode

State: OFF
Input: {topic: "toggle"} → Output: {payload: true} (now ON)
Input: {topic: "toggle"} → Output: {payload: false} (now OFF)
Input: {topic: "toggle"} → Output: {payload: true} (now ON)

Topic Priority

Input: {topic: "set", payload: false}
→ Output: {payload: true} (topic wins!)

Use Cases

• Manual Override: Latch a manual mode flag until reset
• Alarm Acknowledgment: Latch alarm state until operator acknowledges
• Mode Selection: Toggle between operating modes
• Start/Stop Control: Control a process with set/reset signals
• Memory Element: Remember a state across flow executions

Node Status

Shows current state in the editor:

• SET (ON) - Green dot, state is true
• RESET (OFF) - Blue dot, state is false

Author

sr.rpo

License

MIT