I am in the process of designing an inertial sensing cape for the
Beaglebone platform. The cape will have a 16 bit 3 axis accel, 16 bit
3 axis gyro, 3 axis magnetometer, atmospheric pressure sensor and a
digital motions processor to integrate the sensor Indormation into a
cohesive positional quaternion. (all the chips have internal die temp
sensing too...)
My intention is to provide a sensor platform that will appeal to most
aerial/ground robotics needs while still being financially
attractive. My question is,
"Would most applications need gps as well?"
My worry is that adding gps will increase the cost and complexity
without drastically increasing the functionality that most users would
get from the cape. So this is your chance to speak up and tell me what
you would use. Would you be willing to pay an additional 25 dollars to
have gps? Are there other functionalites that would be appropriated?
My hope is to have the schematics done soon so all feed back would be
appreciated.
Depends on the application. For someone who only needs inertial
navigation, gps will be useless. OTOH for outdoors navigation gps may
be useful. Are you going to sell those capes? You could offer two
versions: one with all sensors, one with some of the sensors not
populated. I think that eliminating gps from the design will make it
much less attractive for a wide range of potential users.
In addition I would like to see two (2) barometers such as ST LPS001WP, for example, a GPS/Galileo/Glonass/QZSS receiver such as ST STA8088EX, for example, and a proper I2C connector for off-board sensors. An RGB LED for indications would also be handy as well as a few processor readable jumpers.
Would be interesting to see your block giagrams and schematics for comments…
Thanks for the feedback Seppo and Jacek. To answer your questions,
1) Yes I hope to sell the capes. So I am trying to walk a fine line
between a board that is amazingly feature rich vs just unnecessarily
expensive. Especially because I don't have a viable sense of the
market.
2.) Seppo, what application are you envisioning where (2) barometers
would be helpful? Also, my plan is to use the bmp180 from bosch.
3.) I am looking into different GPS chips. Seppo, I cannot find the
STA8088EX in stock anywhere.
4.) There are already four user controlled LED's on the beaglebone. I
don't know how beneficial another status LED would be if it was buried
in a stack of capes.
Don't worry, I will post my schematics for review.
Just a fast answer, see below.
Maybe you should rank all the nice stuff and
put those of highest rank that there is room of to the board.
Thanks for the feedback Seppo and Jacek. To answer your questions,
Yes I hope to sell the capes. So I am trying to walk a fine line
between a board that is amazingly feature rich vs just unnecessarily
expensive. Especially because I don’t have a viable sense of the
market.
2.) Seppo, what application are you envisioning where (2) barometers
would be helpful? Also, my plan is to use the bmp180 from bosch.
In avionics you want to measure the static AND the dynamic
preassure. You can then calculate your air speed.
3.) I am looking into different GPS chips. Seppo, I cannot find the STA8088EX in stock anywhere.
Sorry, I don’t have any idea about the status of that chip!
4.) There are already four user controlled LED’s on the beaglebone. I
don’t know how beneficial another status LED would be if it was buried
in a stack of capes.
Could be on the edge of each cape (on a standard location)
as should be the jumpers…
Since you're able to stack capes, I'd say lets have a separate GPS cape and then you should be able to fit more sensors on your cape. Keep each type of thing on a separate cape... i.e. Sensors on one cape, communications on another. that way your sensor cape could be used in more situations. i.e. Balloon flights can use the GPS and Cellular, while HVAC types could use Wireless or Zigbee.
The more modular the system, I think, the more functional and customizable the BeagleBone you'll have.
As always in engineering, here again we have the dilemma of
modularization vs. integration.
I would say that priorisize the functions taking in account their
joint use and put as many top priority things on the board
as there is comfortably room on the cape.
I agree with your comments as well… while mine were what shouldn’t be included on a board, what IS included is also important.
I would love to see a “weather” cape. i.e. all the sensors needed to monitor the immediate environment. Temp/Light/Humidity/movement, etc…
I do have one concern with Stacking. What order may be required in the stacks. i.e. if you add a wireless or GPS cape… how will it be affected in the stack in the case of pairing it up with the “Weather” module. If GPS is on top, Light sensor may not work as good, whereas, if the GPS is underneath, will it not get as good a signal. Therefore, I’d like to make a design recommendation that things that need to interface with the immediate surroudings need to be pointed to either top or bottom of the cape, that way light can be viewed from the side and not in the middle of the cape. GPS should include an external antenna mount so as to mitigate that issue
Is there a document that anyone has created on design tips yet? I’d recommend the above be submitted to add to it.
I'd perhaps look at keeping functionally similar things on a single
cape. Like GPS I'd pair with gyros etc, realistically, someone who
buys the cape is going to do so for a purpose and 90% of the time want
to use related functionality.
On another note will you be selling any Batman or Superman Capes?
Thanks for the feedback. You brought up hard but important decision
points. I decided that GPS should be included in the design. So here
is the final sensor list for the Inertial/Motion Sensing Cape.
1.) MPU-6000- 16 bit 3 Axis Accel, 16 bit 3 Axis Gyro, Internal DMP
Engine, 400 Khz i2c bus, ...
2.) BMP180 - (1) Barometric Pressure sensor with .17 m altitude
resolution. Sorry Seppo, I don't foresee anyone using two without
imposing extreme mounting constraints. 400 Khz i2c bus.
3.) HMC5883L- 3 axis magnetometer with a 12 bit adc provides 1-2
degree compass heading accuracy. Heading information is incorporated
into the MPU-6000's quaternion matrix.
4.) Venus638FLPx-L GPS- 20 Hz update rate, 2.5 m accuracy, 29 second
cold start, 1 second hot start, -148dBm cold start sensitivity. I am
planning on including a back-up battery connector for the GPS.
Additionally, I am going to provide a SMA connector for a user select-
able GPS antenna. The antenna connector will be exposed near the
micro-sd card.
I will publish schematics when they are in a decent place. Thanks
again for the feedback. I appreciate it and it definitely helped hone
in on the intent and anticipated uses of the cape.