Re: Small low-cost embedded board for model airplane

On 23 Sep, in article
<1159077661.584590.144500@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
albertgoodwill@xxxxxxxxx "Albert Goodwill" wrote:

Hello Embedded Experts,

For a real-time signal monitoring and logging application, I am loking
a small, low power and light weight microcontroller board. This board
will be carried on a remotely piloted model airplane. As the airplane
flies it will collect data from various sensors and save them to a SD
memory card as well as it will send selected data to the ground for
data logging and monitoring.

I think your requirements below are very optimistic and your main
requirement of low power and low weight will not be met by an off
the shelf board.

Once all the wiring, sensors (and their boards), shielding (for A/D
at least due to local transmitter), your weight and power problems
will be back to bite you. Even the weight of the SD card and its socket
have to be included in the calculations.

Can you recommend any embedded board which can satisfy the following
requirements?

I think you have two choices

Reduce your requirements and sensors to start off

Design your own board for the specific task.

THX,

Albert Goodwill
AlbertGoodwill @ yahoo . com

Requirements
============
* ADC (Analog to Digital Converter)
13 channel (simultaneous sample hold is desirable)
16 bits resolution
it will be used to capture 1000 samples/ second

Simultaneous sample and hold is rare on off the shelf embedded boards and
even rarer on low power and low weight. Considering that most of your
sensors operate in Hz or 10's of range, your sampling rate is 76Hz per
channel which seems over the top to me. Higher A/D sampling rate means more
calculations per second, which means more power used by CPU etc.

I would have expected for these types of sensors a sampling rate of
10 to 20Hz per channel giving 130 to 260 samples per second.
Considering the nature of the sensors being slow response and the
application simultaneous sample and hold seems unnecessary.

* I2C interface
* SPI interface

Some microcontrolelrs have these built in (to varying degrees of
useability), and this can be bit banged, external single chip controller
or even PLD.

* 4 X UART

I can see a need for 3 UARTs, not the fourth. Adding the extra UART
requirement, reduces your choices of boards/microcontrollers.

* Free (or low-cost) C compiler and SW development environment

There are lots of microcontrollers that have ports for GNU compiler
see www.gnu.org


Following are the sensors to be connected to the embedded board
Sensors with analog outputs
* 3 axis accelerometers (0-5v or 0-3.3v analog outputs)
* 3 axis gyros (0-5v or 0-3.3v analog outputs)
* 3 axis magnetosensors (0-5v or 0-3.3v analog outputs)
* 2 pressure sensors (0-5v or 0-3.3v analog outputs)
* 2 current sensor (0-500mv outputs)

Except for the current sensors, the rest have response times, that mean the
output changes if you are lucky at 10Hz. See comments above about A/D.
I actually doubt that the current sensors (probably for measuring
power supply load to this board and main radio control) actually need to
be monitored more than 1Hz anyway.

Keeping your transmitter frequency out of the sensors and wiring will be
interesting.

Unless your airplane is flying at exceptional altitudes (1000's of feet)
or doing very high speed manoeuvres the signals coming out of the sensors
are going to be a very small part of the sensor ranges and will need
amplification before sampling.

RMP Sensor
* 0-10000 RMP sensor with 1 logic pulse per rotation

Which means you have a timer/counter, counting pulses and reading the result
every second at the fastest with range of 0-167 pulses per second, which you
can moving average to gain the rpm.

Fuel Consumption sensor
* 1 logic pulse per xx milliliter fuel flow

Similar approach to rpm, but becomes a running total (or running subtraction)

Sensors with I2C iterface
* 10 temperature sensors with I2C

Thats a lot of wiring as each sensor requires 4 wires, might not another
a/d convertor reading thermistors be easier and lighter. Also how do you
keep the transmitter out of the sensors and their wiring.

Other Sensors
* GPS receiver (accepting DGPS correction) with RS232 interface

Have you totalled up the power consumption of all your sensors, GPS and
secondary transmitter? Then seen what power budget (battery size) that
will need for your expected time duration before adding any form of
embedded board?

I think you will be surprised how much power they require and then
how much the battery weight will be for them alone.

Then see what you can find for computer control.

--
Paul Carpenter | paul@xxxxxxxxxxxxxxxxxxxxxxxxxxx
<http://www.pcserviceselectronics.co.uk/> PC Services
<http://www.gnuh8.org.uk/> GNU H8 & mailing list info
<http://www.badweb.org.uk/> For those web sites you hate

.

Relevant Pages

  • Re: Small low-cost embedded board for model airplane
    ... flies it will collect data from various sensors and save them to a SD ... You did not say if your signals are AC or DC. ... chip since most low size and low power MCUs only have 2 UARTs. ... BTW, when you specify things like small, low power, light weight, you ...
    (comp.arch.embedded)
  • Re: Small low-cost embedded board for model airplane
    ... flies it will collect data from various sensors and save them to a SD ... You did not say if your signals are AC or DC. ... chip since most low size and low power MCUs only have 2 UARTs. ... BTW, when you specify things like small, low power, light weight, you ...
    (comp.arch.embedded)
  • Re: Low cost weight sensor ?
    ... Anton Erasmus wrote: ... Springs, levers and opto or hall sensors would ... There must have been four pressure sensors in the pillars since wires went there and there was neither any mechanical cantilevering nor did this thing move down at all if I stepped on it. ... down and reset the counter when no weight is present. ...
    (comp.arch.embedded)
  • Re: Low cost weight sensor ?
    ... Springs, levers and opto or hall sensors would ... down and reset the counter when no weight is present. ... One then measures the amount of deflection, ...
    (comp.arch.embedded)
  • Re: Need to supply power to 8 sensors. What is the best way?
    ... mA max, I could use a supply with multiple DC power outputs, (eight I ... The sensors will take what they need; ... signal conditioning electronics, and as such the power consumption will ... And well this is my first time supplying 8 ...
    (sci.electronics.design)