Project Status
Flight Tested on F08L01 and ongoing
Project Statement
Ginger is a bidirectional cross-band data routing system which provides wireless access between capsules and the ground via 2.4ghz radios on what are known as Allspice Nodes. These nodes send data to the ginger capsule which then relays the commands to the ground through a high power 70cm link, and vice versa. The allspice network currently transfers data at 250kbps, though the ground link bitrate may change. Store and forward is not implemented in the ginger capsule, and it is up to the allspice node to provide such functionality in the event of a ground link loss.
The communications team seeks to provide every capsule/experiment with an allspice node to allow access to this versatile real-time network. All allspice nodes are designated a three letter callsign. Allspice nodes are allowed to use more than one callsign in rare cases to provide data separation between experiments which share a node, or specialized operations such as GPS data broadcasting.
Design Features
- V1 Nodes are 2.54 cm x 3 cm
- V1 node Cost is US$26
- Output power is 1mW
- bitrate is 250kbps
Performance
- Allspice processors run at 9MHz
- All external IO is bitbanged, and is slow for now
Allspice Nodes Built
TMP
Flight Tested on F08L01
- Node cut out at -30 C on F08L01. Reason is unknown, dry ice test is scheduled.
- Node TMP is a capsule-less experiment designed to test the limits of the technology. This node is subject to temperatures below -70 degrees C. It contains a high precision 10k thermistor as well experiments to validate connectivity. This is the first node ever built.
PRS
Flight Tested on F08L01
- Node PRS is a sensor experiment which resides in a micro-capsule. The micro-capsule is 7cm x 5cm x 5cm and is designed to be clipped or hung from an inter-capsule support line. PRS contains an external pressure sensor and an internal temperature sensor.
- This node contains a 5V charge pump to interface with a 5V sensor.
GPS
Not Flight Tested
- Node GPS uses an EZ430-RF2500 target board to read and decode NMEA data from a UBLOX-5H (lea) module. The data is then translated into ginger packet form and sent out at a programmable interval. Rough temperature measurements of the IC are also sent out at a separate but programmable interval.
- This Node is likely more temperature sensitive due to the GPS chipset and should probably be kept in a micro-capsule. Heaters are most likely not required but flight testing will determine this.
Todo
- Discover why TMP cut out at -30 C. Is this a processor limitation or is this a radio frequency drift issue. Is it both?
- Characterize the in-chip temperature sensor and thermistor with dry ice for a more accurate fit at low temperatures.
Bugs
V1
- CC2500 DVDD pin is not wired correctly, easy greenwire fix between vias.
Insights
- V2 nodes should have onboard 5V charge pumps and more ADC channels wired out.
- TI has released a wireless dev kit that, while somewhat stripped down, would work as an allspice node as it is based on the CC2500. At $20 it is somewhat cheaper than the current allspice nodes and is already populated.
- Allspice nodes using MSP430F2xxx chips with dual uarts would mean less software required for interfacing with I2C, SPI, UART and at faster speeds.
- TI EZ430-RF2500 would make great simple nodes.
