Generic rocket/vehicle/aircraft telemetry/instrumentation payload package

[Luke Weston]

Hi guys,

Just wanted to get your thoughts or opinions on a little something I've been sketching up recently.

https://github.com/lukeweston/SSRPGenericTelemetryModule

The layout of the main board has not been done yet although the schematic is complete. I still need to make some tweaks to the Venus638 peripheral GPS receiver board, it's not finished yet. And yes, the readme and documentation is pretty lacking... I'll fill that in in more depth soon, when I get around to it.

This was originally drawn up around the basic desirable requirements we already had on the wiki for the ASRI SSRP program, for a general-purpose, reusable sensor/instrumentation package for ASRI's student Zuni/Sighter flights, but it has potentially broad applicability to a range of other extra things where a portable, compact, battery-powered sensor/datalogging module with high-performance RF telemetry capability is wanted, for other applications such as rockets, vehicles and aircraft in lots of different research or education situations.

This hardware platform has the following capabilities/components:

- Micro-SD card for removable datalogging and storage.
- Real-time clock with battery backup.
- USB interface for battery recharging as well as PC-based communications, programming, debugging or data analysis.  
- Barometric pressure sensor (30,000 feet approx. maximum).
- 3-axis MEMS gyroscope.
- 3-axis accelerometer.
- 3-axis magnetometer.
- Single-axis high-range accelerometer (up to 200 g-units) for rocket motor characterization in addition to the lower-range, more sensitive 3-axis accelerometer.
- Differential pressure transducer for pitot tube airspeed measurement.
- Temperature sensor.
- Central microcontroller (Atmel ATmega2561).
- On-board Silicon Labs Si1000 microcontroller with integrated UHF transceiver (100mW transmit power in the ~900 MHz spectrum).
- Power supply from a single 3.7V lithium-polymer cell, with on-board recharge control.

- 8 channels of 0-4096mV analog data acquisition from additional external payload electronics. (50 ksps total at a 2.7V power supply, probably a little bit higher than that at 3.3V, so that's at least  6.25k samples per second for each of the 8 individual ADC channels... but that's pretty firmware dependent, it assumes the microcontroller is not busy with anything else and the SPI bus is not occupied talking to any of the other devices; that's only what the MCP3208 ADC itself is capable of which isn't really a realistic metric.)

- Support for a range of different GPS receiver modules and different antenna types, mounted away from the main board to provide more flexible antenna mounting without having the loss of a microwave cable between the GPS antenna and the chip.

- Support for a range of different external RF telemetry hardware if more performance is desired than the on-board Si1000 can provide from its internal RF chain. For example, the RFDesign RFD900 900 MHz RF modem can be used, which consists of a Si1000 microcontroller with external RF front-end LNA/PA etc, providing telemetry ranges of up to nearly 100 kilometers with line-of-sight.

- In any of the above cases, whether the on-board RF chipset is or an external Si1000-based solution is used for the telemetry, all the radios can use essentially the same firmware, such as the SiK firmware developed by Tridge and others for the Si1000 microcontroller.

Any ideas, thoughts or comments about this? I'd appreciate any ideas or feedback you'd like to discuss.

Regards,

  Luke

[Stuart Young]

Had a quick look over just the SSRP module schematic and it looks really good.

Quick Q: Would it be hard to break out the reset line so that you could use that same output from the MCP130T-300I to reset something else (eg: a peripheral built for this device), and/or isolate the MCP130T-300I completely from the ATMega 2561?

I could see cases with peripherals where you may want to capture the reset, do stuff, THEN reset the AVR yourself once you're done. Really a 2 pin 0.1" header that a link/header could be placed on (and a on-board bridge by default that you could cut if you wanted to use the header) would probably be sufficient. Without the track cut, it gives you access to the pins, with the track cut, you can put your own circuitry between the MCP/AVR as required.

PS: Noticed you used an FTDI chip. Any known issues with availability on those?

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[Luke Weston]

I used the FTDI FT230X, which I want to try out because it seems attractive - it's claimed to be faster than the FT232, it's smaller, lower pin count and it's also significantly cheaper - also cheaper than an ATmega8U2 or similar. Also has a lower external component cost than ATmega8U2 - no crystal etc.

DigiKey currently shows no stock of the 768-1153-ND, but I'm not sure if that's just a temporary thing or indicative of some fab supply issue.

Agree with you on the reset stuff - suffice to say, thinking about reset management such as brownout detection, WDT, and all that sort of stuff and throwing a reset to the microcontroller(s) when desired is worth thinking about well in this sort of application.

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[Andy Gelme]

hi Luke,

On 2013-02-21 04:26 , Luke Weston wrote:
> Just wanted to get your thoughts or opinions on a little something
> I've been sketching up recently.
> https://github.com/lukeweston/SSRPGenericTelemetryModule

That's a nice piece of work.

> - 3-axis MEMS gyroscope.
> - 3-axis accelerometer.
> - 3-axis magnetometer.

Consider using a single 9DOF IMU chip, like the Invensense MPU-9250 or
MPU-9150 ?

http://invensense.com/mems/gyro/nineaxis.html

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