LCD screen shows "-999" value instead of real measurement value

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LCD screen shows "-999" value instead of real measurement value

AlfredC
Administrator
This post was updated on .
Value "-999" is indicative of sensor reading failure. You should never see this value on the LCD screen.

Sensors connected to LiV are configured in the ON_BOARD_SENSORS section of "~/liv/livDB/livDB.config" file. If a certain sensor is configured as "No", then livDB process will not initialise and read that particular sensor, but write a -999 value in liv sqlite Data Base.

When livLCD process starts, it will first look at livDB.config file, and it will skip displaying measurements for sensors that are configured "not present" on the board. If you see the -999 value for one of your sensors being displayed on the LCD screen, it means that the sensor is configured as "present" and livDB failed to read any measurements out of that sensor.

Here is what to do if you experience the -999 issue with one of your sensors:
1) make sure the sensor is connected to the board
2) make sure the sensor is properly connected to the board (please refer to photos on "LiV DIY assembly" page for the correct orientation of the sensor)
3) go to "~/liv/livDB" directory and test reading sensors with the following commands:
- "sudo python airPressureSensor.py" (for BMP 180 sensor)
- "sudo python co2Sensor.py" (for K30 sensor)
- "sudo python temperatureHumiditySensor.py" (for DHT22 sensor)
If you see any errors, try fixing them (e.g make sure your sensor is configured to the right GPIO number in livD.config file).

If you are using LiV RPi on a Raspberry Pi model B or B+, you will see the -999 value for the temperature and humidity sensor even if the sensor is plugged in properly and it has the right GPIO number setting in the configuration file. This is because LiV RPi image on the SD card works out of the box with RPi model 3 and 2. If you have a Raspberry Pi model B or B+, you need to do some additional settings:
- "cd ~/liv/livDB/Adafruit_Python_DHT"
- "sudo python setup.py install"
- "sudo shutdown now"
-  turn power off and back on








 


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