BEXUS
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Previous BEXUS flight information from Stratocat - http://www.stratocat.com.ar/fichas-e/2006/KRN-20060619.htm

Experiment information
The experiment interface has been kept as simple as possible. The users only have some things to keep in mind when designing there experiment. The users interface has following features:

MPEG -> Experiment : Housekeeping interface
The platform offers the experiments three power supplies: +5, +12, and -12 V. The three supplies can be maneuvered individually and have short circuit protection and over current protection. The maximum current output of the supply is 2A on the +5V output, 1 A on the +12V and -12V output.

This is however depending on the number of experiments using the supply. If there are too many sharing it, the maximum output will lowered for each experiment. Consult the platform operator or project manager when defining the requirements for the experiment. The total power for the flight is 260Wh. It's recommended to design your experiment PCB such as the experiment rack can be used. Use a PCB with dimensions 160mm x 100mm.


160x100 PCB placed in the experiment rack.

Experiment -> MPEG : Data interface
Protocol: UART via RS232
Handshaking: HW - RTS
Baud rate: 9600 bps
The experiments have a serial data interface with the platform and the up/downlink. The system is using UART via RS232 with a simple hardware handshaking protocol. The handshaking consists of a channel that tells the experiment if it's ok to send data or not. A logical one on the RTS states that it's ok for the experiment to send 1(one) byte of data to the ground station. A logical zero means that the node will not respond to the data transmitted and any data sent during this time will be lost. The communication baud rate is 9.6 kbps. The downlink consists however of 2 independent 9.6 kbps channels. These are shared by all experiments.

There will also be 3(three) independent digital control signals to the experiment. These are using TTL levels. The output current should not exceed 20 mA. Over loading or short circuit may damage the node.

Experiment -> E-LINK : Data interface
Protocol: UART via RS422
Handshaking: None
Baud rate: 9600 bps
There is a possibility to not send the experiment data through MPEG but directly through the E-LINK up/downlink system. The experiment should then use the RS422 protocol and there is no need for any handshaking. Note that the three independent digital control signals from MPEG still can be used via the MPEG connector.

Experiment -> MPEG : The connector
The experiment will use a connector to interface with MPEG.
For the connector on the experiment hardware use following specifications:
- 15 pin DSUB.
- Male type.
- Use panel mounted connector with wires to the PCB. No PCB mounted connector.
- Use the pin numbers in the connector.



1) Interlock in. Connect with wire to pin 15. No connection to experiment circuitry.
2) RTS. Serial data flow control.
3) TX. Experiment transmit output.
4) RX. Experiment transmit input.
5) GND1.
6) Digital output 0.
7) Digital output 1.
8) Digital output 2.
9) GND2.
10) 5V.
11) GND3.
12) 12V.
13) GND1.(same as pin 5)
14) -12V.
15) Interlock out. Connect with wire to pin 1.

The interlock between pin 1 and 15 must, as said above NOT be connected to any circuitry on the experiment. A direct jumper cable in the connector itself is recommended. It is also recommended that no circuit board mounted connectors are used. Instead use a panel mounted type with cables from the connector to the circuit board. This will produce less stress on the soldering.

Pin 5 and 13 are both GND1 and either or both can be used. Which ground to use will however be decided by the platform manager, so don't do permanent designs for this before consulting. The Tx and Rx are the experiments transmitter output and receiver input. Note that theese will not be used if the experiment sends data directly to the E-LINK system. All cables between the experiments and MPEG or E-LINK will be provided by the platform manager.


Panel mounted connector and interlock.

Experiment -> E-LINK : The connector
The experiment will use a connector to interface with the E-LINK up/downlink system.
For the connector on the experiment hardware use following specifications:
- 9 pin DSUB.
- Male type.
- Use panel mounted connector with wires to the PCB. No PCB mounted connector.
- Use the pin numbers in the connector.




1) TX +.
2) TX -.
3) RX -.
4) RX +.

In the E-LINK end, there will be a military type 12, 8 pin connector. All cables between the experiments and MPEG or E-LINK will be provided by the platform manager.

E-LINK up/downlink system explanation