Sensor module - advice needed!

DarrenY

Hi Folks,

I am attempting to put together a sensor box for use in gliders/aircraft that will feed a PDA with various information such as GPS position, pressure altitude, rate of climb (variometer), compass heading, roll, pitch and yaw, all via a single serial hybrid-NMEA output.

I have been looking at the Parellax website all day trying to work out how I could plug it all together and was hoping that you could offer me some advice as to the way forward.

Here are the components that I was thinking of using:

Non-Parellax:
Pressure sensor: Motorola MPX100 series silicon piezoresistive pressure sensor
ADC: Analog devices AD7710 (http://www.analog.com/en/prod/0,,AD7710,00.html)
GPS: Holux M-89 Engine Board (I wanted more than 12 channels and SirfStarIII)

Parellax:
Processor + motherboard: Advice needed!
Hitachi HM55B Compass Module
Hitachi H48C Tri-Axis Accelerometer

I need some advice as to how to hook all these up. I understand that each Stamp, module has 2 serial i/o, of which 1 will be taken up by the output to the PDA, leaving just one to use to connect to all 4 of the sensors (GPS, ADC, Compass, Accelerometer)

To sum up my post, I want to connect 4 serial devices to a Stamp module, combine all the individual outputs into 1 hybrid NMEA output (NMEA is just a series of text sentences) and output every 1 second (or maybe 0.5 second..)

Can this be done, and if so, what stamp module/motherboard would you suggest.

For info, I am a C/C++/C# software engineer with limited hardware/electronics experience. If possible I would like to use C, but don’t mind learing BASIC or SPIN if needed....

Thanks All!


NOTE: For the future, I might want to add data-logging to it as well, maybe to a CF or SD card.

Franklin

Any I/O pin on the stamp can be configured as a serial line at TTL levels so that should not be a problem. For ease of use while building and testing the board of education will be a good choice and any of the stamps would work but the BS2Pxx chips have some features that migh come in handy if you decide to change sensors.

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- Stephen

Tracy Allen

Like Franklin says, you are in luck in that the Stamp can use any of its i/o ports for bidirectional serial data, plus in addition there is the debug/programming port that is also available for general purposes. On th down side, the serial ports are not buffered, so, for example, one serial port can't be waiting for and receiving a sentence from the GPS while the BS2 is off doing something else. It sounds like you have a lot of elements to add to your project. Each one on its own is straightforward enough, but you will have to learn PBASIC and chop off the pieces one at a time. Then the integration will be a challenge and to meet the once per second goal. The way I see it, the operation would be synced to the reception of the GPS data, followed by the sensor reads, followed by construction and output of the new sentence. I'd definitely start with the BS2p. You cannot do C on the Stamp--only PBASIC. If you have the budget for it, the professional development board has a lot of built in peripherals to help you get up to speed, and a lot of real estate for sensors. There is a nice SD card interface available from Hitt Consulting that makes the card interface very easy.

The Propeller is also a good option. You could go further with the Prop, because it can multitask and there would be no question about it being able to handle all the timing constraints and the suite of sensors. It does have a steeper learning curve, at least at first. There are several demo and development boards avaiiable, both from Parallax and from independent sources, and I believe Imagecraft plans to have a version of C for the Propeller out by the end of the year. Still, you would want to learn some Spin and assembly to get the picture of what goes on inside.

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Tracy Allen
www.emesystems.com

DarrenY

Thanks!

It sounds like the Prop might be the way to go - I could allocate a cog to each sensor and one for the i/o.

Thankyou for your advice - I am sure I will be back here soon with questions of a more detailed Prop nature!!