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copacetic353
01-09-2009, 07:47 AM
Hello all,

I am a part of a research and development group at a University and I've been recently dispatched to build a system that points an antenna at a moving object.

Basically, I will be mounting the antenna on a tripod stand and I plan on using two motors to control orientation. One motor will control the 360 degree movement about its vertical axis and the other will control the antenna's pitch between 0 and 90 degrees.

I plan on using the propeller MCU and the propeller control board. I am going to be installing a GPS unit and a compass unit on the control board for real time tripod coordinates and direction so that I will not have to change the code every time the tripod's location is changed.

Upon brainstorming the design, I have come up with two problems (so far) to which I am not sure the solution.

1. I know how to detect the direction that the antenna is pointing using the compass module that I will be installing. However, I am not sure how the detect the anenna's position on its tilting axis from 0 to 90 degrees. Any ideas?

2. The system that I am building will be getting streaming data from a ground station via (probably) a serial connection. I don't know if this is even possible with the propeller and if so how to do it?

Thank you for your time!

SRLM
01-09-2009, 07:55 AM
1. You can use an accelerometer, a potentiometer, or a rotary encoder.

2. If it's serial communication, then you can just use one of the OBEX objects.

copacetic353
01-09-2009, 07:58 AM
Are there parallax motors that come with rotary encoders that are interfaceable with the propeller?
How could I use the accelerometer do detect position and I am not sure what a potentiometer is?

copacetic353
01-09-2009, 07:59 AM
If I am using serial communication is there a certain format the info needs? I am not very good at system interfacing.

Kye
01-09-2009, 08:00 AM
Check out parallax's store, and sensor's section. Parallax has a few articles describing how to use an accelerometer to get angle measurements.

Also the propeller chip is a very over powered microcontroller. It can do alot more than you think. Serial communication is very easy for it.

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Nyamekye,

Kye
01-09-2009, 08:03 AM
http://www.parallax.com/Store/Sensors/AccelerationTilt/tabid/172/CategoryID/47/List/0/Level/a/ProductID/93/Default.aspx?SortField=ProductName%2cProductName

http://www.parallax.com/Store/Sensors/AccelerationTilt/tabid/172/CategoryID/47/List/0/Level/a/ProductID/97/Default.aspx?SortField=ProductName%2cProductName

http://www.parallax.com/Store/Accessories/MotorServos/tabid/163/CategoryID/57/List/0/Level/a/ProductID/507/Default.aspx?SortField=ProductName%2cProductName



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Nyamekye,

copacetic353
01-09-2009, 08:05 AM
Will the Hitachi HM55B Compass Module work with the propeller?

copacetic353
01-09-2009, 08:05 AM
Thank you SRLM and Nyamekye!

Kye
01-09-2009, 08:19 AM
Check out the object exchange also:

http://obex.parallax.com/

You can find prebuilt drivers here and stuff here. The sensors section and motor control section will make you're life easier.

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Nyamekye,

sosaraujo
01-09-2009, 08:30 AM
check this guide:
www.dimensionengineering.com/accelerometers.htm (http://www.dimensionengineering.com/accelerometers.htm)

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-------
Adrian Sosa Araujo.- San Luis, ARG - Time Zone (GMT -3)
El planteo de un problema es mas importante que su solución.

SRLM
01-09-2009, 01:43 PM
Any of the sensors that I mentioned will work with the propeller. In fact, pretty much any sensor at all you can figure out ways (perhaps with some additional hardware in extreme cases) to hook it up to the propeller.

A potentiometer is a variable resistor. It's usually in the format of a dial (think stereo speaker volume knob).

Parallax only has one prebuilt system with both a motor and encoders, and that's the wheel and motor mount. However, I don't think that will be best for you, since the resolution is a little low and the price is pretty high (for what you're looking for). The easiest solution and most reliable would be to make your own disk to look something like the following. The use a simple IR beam to determine when the slots pass. Note that this disk only gives you the speed, not absolute position. If you absolutely need the absolute position, then you'll need to make a much more complicated disk. If you don't, you can make an assumption about where it is based on (perhaps) limit switches.

http://www.sscnet.ucla.edu/geog/gessler/topics/encoder-sharp.jpg

Most RF devices (at least the complete solution types) offer as simple serial interface that you can use directly. It's not a problem, and requires only a couple lines of code on your part.

StefanL38
01-09-2009, 04:11 PM
Hello copacetic,

welcome to the forum.
You are free to ask questions as many as you like. You will receive help here.

My personal opinion is: as you are a member of a research and development group at a University it's up to you to do the details.
Every chief you might be working for after university expects that you can solve problems completely on your own.
(without asking the chief about details but of course asking other people that are experts to something)

The propeller can do really a lot. You can even connect a SD-card to store data on it.
If you're planning to process megabytes of data in very fast realtime (datathroughput more than 10kB/second)
there is a limit. Most other things are no problem. The Prop can even handle highspeed signals and frequencies.

The propeller is able to send and receive data at 115200 Baud = 14 kB/second
For send/receive kilobytes of data continuosly without any interruptions it will be a challenge
to keep the receivebuffer from overflowing

Send/receive at slower datarates and smaller datapackages than 10 kB that are coming in / going out intermitend are no problem

The prebuild program-code in the object-exchange save a lot of work and time.

BUT from your question I got the impression that your knowledge about programming and electronics is on a very basic level.
Without a medium knowledge about programming and elecronics - to say it positive - you have A LOT to learn.

As you are a group of students think about engaging one or two new members that have good skills in programming
(the programming-language doesn't matter they will get into the propeller-language called SPIN within two days)
and somebody with good knowledge about electronics.

best regards

Stefan