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Optional: OAT Temperature Sensor

An outside air temperature (OAT) sensor allows OnSpeed to compute density altitude and true airspeed corrections without relying on EFIS data.

When You Need One

  • No EFIS connected — if you're running OnSpeed standalone (no Dynon, Garmin, or MGL), the DS18B20 OAT sensor provides the temperature data needed for TAS corrections
  • EFIS doesn't provide OAT — some older EFIS units may not output OAT on the serial interface

If your EFIS provides OAT data via serial (Dynon SkyView, Garmin G5/G3X, MGL all do), you probably don't need a separate OAT sensor — select the EFIS OAT source instead. When the selected source is unavailable, OnSpeed falls back to the ISA standard-atmosphere temperature for the current pressure altitude.

Hardware

  • DS18B20 digital temperature sensor (OneWire protocol)
  • Waterproof probe versions are available and recommended for aircraft use
  • Accuracy: ±0.5°C from -10°C to +85°C

Wiring

The DS18B20 connects to the controller via the OneWire protocol. The data pin differs by hardware variant: GPIO 3 on V4P, GPIO 14 on V4B.

  1. VCC → 3.3V or 5V from the controller
  2. GND → Ground
  3. Data → OAT pin (GPIO 3 on V4P, GPIO 14 on V4B)
  4. Add a 4.7kΩ pull-up resistor between Data and VCC (required for OneWire)

Mounting

Mount the sensor probe where it will measure outside air temperature:

  • Outside the cabin — in the airstream, not inside the cockpit
  • Shielded from direct sun — solar radiation heats the sensor and gives false readings
  • Away from engine heat — don't mount near exhaust or engine cowling
  • In moving air — a location with good airflow during flight (e.g., under a wing root fairing)

Configuration

  1. Connect to the OnSpeed web interface
  2. Set OAT Source to Internal probe (DS18B20) in the configuration
  3. Save and reboot

Verify the sensor is working by checking the SENSORS console command — the OAT reading should show a reasonable ambient temperature.

Runtime configuration

The OAT source is a runtime setting (OATMODE), not a compile-time option. Choose PROBE, EFIS, or ISA from the web interface without reflashing firmware.