UM1479

System overview

Doc ID 022381 Rev 1

21/28

2.1.2

MEMS for freefall and vibration data logging

The LIS3DH is the MEMS device used in this application. The LIS3DH MEMS device has

been used to identify a freefall event and a vibration level event for the data logger board.

Whenever the data logger board undergoes a freefall, the date, hour, and minute of that

instance is logged inside the EEPROM as a freefall event.

For a vibration event, 5 levels are defined based on the empirically observed results of the

MEMS output for shaking the data logger board. These levels are defined as: highest

sensitivity, high sensitivity, medium sensitivity, low sensitivity and lowest sensitivity.

In the case of Event Logger mode:

The threshold for the vibration level is defined using the GUI and the RFID reader. When the

vibration seen by the data logger board is equal to or greater than this threshold, the value is

logged as a vibration event along with the date, hour, and minute of the event.

In the case of Data Logger mode:

At every second, board vibration is checked and the value is logged inside the EEPROM. If

there is no vibration on the board, it is logged as no vibration level in the EEPROM.

2.1.3

Humidity sensor for percentage humidity data logging

The HIH-5030 is the humidity sensor from Honeywell. Output of this sensor is analog

voltage which is measured using ADC of the STM8L microcontroller and then converted into

percentage humidity.

In the case of event logger mode:

Maximum and minimum threshold values for percentage humidity are configured using the

GUI and the RFID reader. In the event logger system, the humidity value is calculated every

1 second, and if this value is outside the configured threshold values, it is logged inside the

EEPROM along with the date, hour, and minute of that instance.

In the case of data logger mode:

At every second, the humidity value is calculated and stored inside the EEPROM.

2.1.4

Photo sensor for light data logging

The APDS-9004 is a photo sensor which is used to sense the ambient light in the data

logger application. Output of the photo sensor is an analog voltage which is measured using

ADC of the STM8L microcontroller.

For light intensity logging, 5 levels are defined based on an empirically observed voltage

level output of the photo sensor circuit. These levels are defined as: dark, semi dark,

normal, bright, and very bright.

In the case of event logger mode:

The threshold for the light level is defined using the GUI and the RFID reader. When the light

intensity as seen by the data logger board is equal to or greater than this threshold, the

value is logged as an event along with the date, hour, and minute inside the EEPROM. After

every second, this comparison of threshold light intensity and present light intensity is done

and then, accordingly, the event is logged inside the EEPROM. This logging of count for light

intensity is checked every 1 second. In the case of data logger mode:

At every second, the light intensity value is calculated and stored inside the EEPROM.