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Temperature sensors.md

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Temperature sensors

It is now possible to measure temperatures with the help of the I²C LM75 and 1-Wire DS18B20 chips. The temperature values can be displayed on the OSD and they are also logged. A total maximum of 8 temperature sensors can be connected. The support is enabled by default on F4 and F7 FCs. To use with F3 FCs you need to build a custom firmware.

LM75

Up to 8 can be connected to the flight controller.

  • Package: SOP-8, breakout boards can be found easily
  • Interface: I²C (max 400kHz)
  • Supply: 2.7 to 5.5V
  • Temperature range: -55 to +125°C

On the purple LM75 (CJMCU-75), address line pins on the bottom of the PCB need to be bridged either to ground or VCC (to define I2C address)

image

Pin definition:

A2 A1 A0 Address INAV add
GND GND GND 0x48 0
GND GND VCC 0x49 1
GND VCC GND 0x4A 2
GND VCC VCC 0x4B 3
VCC GND GND 0x4C 4
VCC GND VCC 0x4D 5
VCC VCC GND 0x4E 6
VCC VCC VCC 0x4F 7

If more than one sensor is used, each sensor must have different address.

DS18B20

  • Package: TO-92, SO-8, µSOP-8
  • Interface: 1-Wire
  • Supply: 3.0 to 5.5V (parasitic power not supported)
  • Temperature range: -55 to +125°C

None of the flight controllers on the market at the time this documentation is written supports 1-Wire directly. To use these sensors a I²C to 1-Wire interface chip needs to be used, the DS2482. Connect the DS2482 SCL and SDA lines to your FC, add a 4.7kohm pull-up resistor between VCC and the DQ pin then connect all the sensors DQ pin to the DS2482 DQ pin.

Configuring temperature sensors

The temp_sensor CLI command can be used to display and change the temperature sensors configuration. When a new temperature sensor is connected it is automatically detected and will appear in the output of the temp_sensor command.

  • temp_sensor without any argument displays all the sensors configuration
  • temp_sensor reset deletes all the sensors
  • temp_sensor index type address alarm_min alarm_max osd_symbol label to configure a new sensor or modify the configuration of an existing one.

Parameters description

  • index is the index of the configuration slot you want to change
  • type can be 1 for LM75 or 2 for DS18B20
  • address is the address of the device on the bus. 0 to 7 for a LM75 or the full 64bit ROM in hex format for a 18B20
  • alarm_min is the temperature under which the corresponding OSD element will start blinking (decidegrees centigrade)
  • alarm_max is the temperature above which the corresponding OSD element will start blinking (decidegrees centigrade)
  • osd_symbol is the ID of a symbol to display on the OSD to the left of the temperature value. Use 0 to display a label instead (see next parameter). See the table bellow for the available IDs
  • label is a 4 characters maximum label that is displayed on the OSD next to the temperature value
Symbol ID Description
1 Generic temperature symbol
2 ESC temperature symbol
3 VTX temperature symbol
4 Motor temperature symbol
5 Battery temperature symbol
6 Exterior temperature symbol

Example output

Example output of the temp_sensor command on a system with two LM75 and four DS18B20 sensors connected

temp_sensor 0 1 0 -200 600 0
temp_sensor 1 1 1 -200 600 0
temp_sensor 2 2 7c0118681e1cff28 -200 600 0
temp_sensor 3 2 7d01186838f2ff28 -200 600 0
temp_sensor 4 2 210118684001ff28 -200 600 0
temp_sensor 5 2 f801186750c7ff28 -200 600 0
temp_sensor 6 0 0 0 0 
temp_sensor 7 0 0 0 0

To set for example the OSD symbol of the first temperature sensor to the ESC symbol:

temp_sensor 0 1 0 -200 600 2

To change for example the configuration of the fourth sensor to label BATT, minimum value alarm 0.5°C and maximum value alarm 45°C

temp_sensor 3 2 7d01186838f2ff28 5 450 0 BATT

Configuring the way OSD temperature labels are displayed

You can use the osd_temp_label_align setting to chose how the labels for the temperature sensor's values are displayed. Possible alignment values are LEFT and RIGHT.

Example

LEFT alignment:
T1   xxx°C
ESC  xxx°C

RIGHT alignment:
 T1 xxx°C
ESC xxx°C