PSAS/ news/ 2006-01-04 - Capstone Team: USB discussion and schedule planning

Communication bus discussion

The old LV2 bus system, on the "bus continuum":

master/slave model < - - -flight computer model- - - - - - - - - - - - - - - - > peer-to-peer model

The Men Micro board only brings out one USB port, but it has 2 CAN nodes. We could go totally USB, or we could put the IMU on one CAN bus, and put everything else on another CAN bus. The last system (where everything was on the same CAN bus), was adequate bandwidth-wise. For more information on CAN bus bandwidth utilization, see this page. It is important to note that we might need more bandwidth in the future.

(!) The avionics team has been kicking around the idea of having a node that monitors the rocket state and turns on a tri-colored LED according to the system state. As far as we can tell, there is no way to monitor the USB bus, unless it's through the host (the flight computer). Messages are intended for only one device, which means there would be redundancy in the messages to the state monitoring node.

USB discussion

USB pros:

A USB node would most likely be self powered. The problem the avionics team had with the last rocket was that the bus voltage was a wide range. When the lithium ion batteries were being charged, the bus voltage could be as high as 20V. It was usually between 10V-15V, but each node needed a specific DC current (9V or 12V, exactly). Thus a switching power supply was needed for each node, to convert the "20V" bus down to the required voltage.

USB fact and question list




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