pwsat-droptower

This project is a part of PWSat2 Drop Tower tests campaign.

This project consist of few parts:

• Arduino UNO board + Arduino protoshield - it is called MainController.
• BackupLogger which logs all transmitted data via an UART by the Arduino board.
• An external electromagnet which is controlled via the MainController.
• Separation switch which detects DropTES-PWSat2 separation. Checked by the MainController.
• Redundant battery pack composed of lead-acid batteries.

Arduino board modes

There are two modes of the Arduino board which are selected with a jumper:

• Free Fall triggering - it detects free fall, next it waits between 20-300ms and it cuts-off an electromagnet.
• Switch triggering - it detects change the switch's state, next it waits 100-500ms and it cuts-off an electromagnet.

In case of accelerometers' failure it automatically change the current mode to switch triggering mode. Any microSD failure doesn't affects on Arduino board mode.

Detecting Free Fall

The ADXL345 accelerometer is responsible for free fall detection.

The ADXL345 library installation and testing:

• For free fall detection with ADXL345 clone the library from GitHub into your Arduino Lib folder.
• Upload the following into the board: code
• Drop the board from min 1-1.5 meters and see the messages in the serial monitor.

Controlling a MOSFET

The MOSFET transistor is responsible for switching on/off the 12V for an electromagnet. It is controller via the D7 port:

• 0 -> electromagnet is ON,
• 1 -> electrmagnet is OFF.

Arduino reset doesn't affect on the stwich.

Writing to SD Card on Arduino board

For writing to SD the extnal Arduino library was used. The library is called SdFat and its much faster compared to the standard one available out of the box.

Executed tests with writing short strings into sd card:

milis	x	y	z	state
1058	7	-35	6	0
1067	8	-37	5	0
1076	8	-35	6	0
1085	9	-33	5	0

• x,y,z - readings from accelerometer
• state - additional data where FF indicates the point where the Free Fall was detected
• milis - time in miliseconds since the program started (used just for testing purposes)

Experiment data:

16.9 MB after 2.5 h of work