Lua Examples

Lua Examples

Worked examples for the Lua Graph Editor. Each example shows the nodes, connections, and generated Lua code. For the full node catalog, see Lua Node Reference.

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Example 1: Low Battery Alert

Goal: Send a warning to the GCS when battery drops below 11.1V.

Nodes

1. Battery sensor -- reads voltage
2. Constant -- value 11.1
3. Compare -- operator < (less than)
4. Debounce -- 5000ms delay to avoid spamming
5. Send GCS Text -- message "LOW BATTERY", severity Warning

Connections

Battery [Voltage] --> Compare [A]
Constant [Value]  --> Compare [B]
Compare [Result]  --> Debounce [Input]
Debounce [Output] --> Send GCS Text [Trigger]

Generated Lua

local WARN_SENT = false

function update()
  local voltage = battery:voltage(0)
  local is_low = voltage < 11.1

  if is_low and not WARN_SENT then
    gcs:send_text(4, "LOW BATTERY")
    WARN_SENT = true
  elseif not is_low then
    WARN_SENT = false
  end

  return update, 1000
end

return update, 1000

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Example 2: Geofence Distance Warning

Goal: Alert the pilot when the vehicle is more than 500m from home.

Nodes

1. GPS Position sensor
2. Constant -- value 500
3. Compare -- operator >
4. Send GCS Text -- message "GEOFENCE WARNING"

Connections

GPS Position [Distance from Home] --> Compare [A]
Constant [Value]                  --> Compare [B]
Compare [Result]                  --> Send GCS Text [Trigger]

GPS Position provides raw latitude/longitude. The compiler calculates distance from home using the ArduPilot ahrs:get_home() API.

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Example 3: Camera Trigger on RC Switch

Goal: Trigger a relay when RC channel 7 goes above 1700us.

Nodes

1. RC Channel sensor -- channel 7
2. Constant -- value 1700
3. Compare -- operator >
4. Rising Edge -- fire only on the transition (not continuously)
5. Trigger Relay -- relay 0, state ON

Connections

RC Channel [Value] --> Compare [A]
Constant [Value]   --> Compare [B]
Compare [Result]   --> Rising Edge [Input]
Rising Edge [Triggered] --> Trigger Relay [Trigger]

Generated Lua

local prev_state = false

function update()
  local ch7 = rc:get_pwm(7)
  local is_high = ch7 > 1700

  local rising = is_high and not prev_state
  prev_state = is_high

  if rising then
    relay:on(0)
  end

  return update, 200
end

return update, 200

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Example 4: Terrain Follow with Rangefinder

Goal: Log rangefinder altitude to a CSV file every 2 seconds.

Nodes

1. Rangefinder sensor -- instance 0
2. Run Every -- 2000ms interval
3. Baro Altitude sensor
4. Log to File -- filename terrain.csv, comma separator

Connections

Run Every [Flow]          --> Log to File [Trigger]
Rangefinder [Distance]    --> Log to File [Value 1]
Baro Altitude [Altitude]  --> Log to File [Value 2]

The resulting CSV file on the SD card contains timestamped rangefinder and barometric altitude data, useful for post-flight terrain analysis.