GPIO Battery Temperature

FALCON supports up to two battery temperature sensors using NTC thermistors connected to GPIO pins. The measured temperatures are broadcast over CAN in the 0x620 - Battery Status message as min/max values.

Thermistor Installation

The thermistor is connected in a voltage divider configuration with a pull-up resistor to the IO reference voltage:

IO +5V ──┤ 3.3kΩ pull-up ├──┬──┤ NTC thermistor ├── IOGND
                                                      │
                                                   GPIO pin

1. Connect a 3.3kΩ resistor between IO +5V and the GPIO pin
2. Connect the NTC thermistor between the GPIO pin and IOGND

warning

The pull-up resistor value and reference voltage are fixed in the firmware (3.3kΩ pull-up, 5V reference). Using different values will result in incorrect temperature readings.

tip

After connecting, verify your wiring by checking the Rthermistor and Vthermistor states in the respective /btemp1/ or /btemp2/ folder. The resistance should match the expected thermistor value at room temperature.

Setup

1. Assign GPIO pins

Configure which GPIO pins the thermistors are connected to in the /io/ folder.

in_btemp1

GPIO ID for battery temperature sensor 1. Set to 0 to disable.

in_btemp2

GPIO ID for battery temperature sensor 2. Set to 0 to disable.

2. Configure thermistor parameters

Each sensor has its own parameter folder (/btemp1/ and /btemp2/) where the thermistor characteristics are configured.

info

The thermistor parameters are located in the /btemp1/ and /btemp2/ folders.

thermistor_r0 [Ohm]

Resistance of the thermistor at 25°C.

thermistor_beta [K]

Beta coefficient of the thermistor. Use a negative value for NTC thermistors.

States

Sensor 1 (/btemp1/)

State	Unit	Description
Rthermistor	Ohm	Calculated thermistor resistance
Vthermistor	V	Filtered voltage reading at the GPIO pin
temperature	°C	Temperature calculated from thermistor resistance

Sensor 2 (/btemp2/)

State	Unit	Description
Rthermistor	Ohm	Calculated thermistor resistance
Vthermistor	V	Filtered voltage reading at the GPIO pin
temperature	°C	Temperature calculated from thermistor resistance