Hm55b

ellizard

HI all.

I'm experimenting with the HM55B Compass Module,
on the HM55ModDocs.pdf in the SX section it is indicated the possibility to obtain the real angle from North in Degree.
The suggested operation is: arctan(-y/x)
But there is no such command or operator in the SX/B.
I have done a search in the Forum but with no results.........
How can I obtain the arctan calculation with SX?

Anyone has a suggestion on how to accomplish this?

Thanks in Advance

Stefano

P.S. Excuse my fat ignorance about math's

CCraig

Stefano,

· I'm doing some research for a upcoming project. I think we have some work cutout for us. First, I'm worst than anybody when it come to math, but here it goes.

There is a SIN and COS example in the SX/B online help. Look in the PWM example. It's got a small table driven lookup. I believe that this is the start we need. That was the easy part.

Now, go to Tracy Allen's web page. If you don't know it, bookmark it well. On this page:

http://www.emesystems.com/BS2math3.htm

He talks about using the BS2 which only has SIN and COS, the two tools we now have. We may have to "glean" through it because the BS2 uses Brads (binary radians), but I think the answer lies within.

HTH, Chris

added:

Well, a little post note. I'm reading the SIN and COS routines in the SX/B and it does use Brads, but I'm trying to figure out if it will work. I have a lot to learn.


Post Edited (CCraig) : 12/12/2006 2:48:20 PM GMT

Bean

Stefano,
· Here is some code I wrote awhile back that reads the Memsic 2125 and calculates the angle using the CORDIC method.

[noparse][[/noparse]edit] "ATAN word.SXB"· uses word variables for much greater resolution. But it doens't have the code for the HM55B. But you could combine the two if you need the resolution.

Enjoy,
Bean.

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Cheap used 4-digit LED display with driver IC·www.hc4led.com

Low power SD Data Logger www.sddatalogger.com
SX-Video Display Modules www.sxvm.com
Stuff I'm selling on ebay http://search.ebay.com/_W0QQsassZhittconsultingQQhtZ-1

"USA Today has come out with a new survey - apparently, three out of every four people make up 75% of the population." - David Letterman

Post Edited (Bean (Hitt Consulting)) : 12/13/2006 2:42:38 PM GMT

ellizard

HI Bean and CCraig

Thanks for replying to mi request...............

Bean
As usual You are always ready with plenty of example and help
I had a torough look at you file HM55 Compass.SXB, and all the comments relates to.......

Program Description said...
' Demonstration of Memsic 2125 Accelerometer (Parallax Item # 28017)
'
' This program will read the X and Y positions from the Memsic 2125 and
' compute the angle and tilt from the values.
'
' I would recommend connecting the 2125 using two LCD extension cables
' (Item # 805-00002,451-00303). This will allow you to turn the 2125 without
' disrupting the SX-Key connections.

I understand tha this file is a derivation of a MEMSIC application, I did not think of using this approach.
There is always to apprehend by this Forum and their clever participants.
But it's not clear how you connected the HM55B Compass Module

Thanks

CCraig
Eventually your maths skills are more better than mine are......
For Brads to Degrees, it's only a small calculation because Brads : Degrees =255 : 360 so there is a direct relation easy to work out
it should be (Brads * 360) / 255 to obtain the value in Degrees.
It has to be computed correctly in order to avoid exceeding 65535 max value admitted for calculations even the intermediate results.

Anyway thanks to you too.
I'll post the results of my effort to solve this issue.

Warmest Regards
Stefano

Post Edited (ellizard) : 12/13/2006 12:09:36 PM GMT

Bean

Stefano,
Oops, That code was for the memsic 2125. I must have changed the name, but never changed the code. Sorry about that.
I will have to see if I have a HM55B.

Bean.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Cheap used 4-digit LED display with driver IC·www.hc4led.com

Low power SD Data Logger www.sddatalogger.com
SX-Video Display Modules www.sxvm.com
Stuff I'm selling on ebay http://search.ebay.com/_W0QQsassZhittconsultingQQhtZ-1

"USA Today has come out with a new survey - apparently, three out of every four people make up 75% of the population." - David Letterman

Yendor

If you wanted to add another IC to your project for trig functions, you could add the umFPU, but I would rather do it in software myself.· It's also kinda complicated to implement.

Note that there's a 8 pin(v2) and a 16 pin version (v3)

http://www.parallax.com/detail.asp?product_id=604-00030

Rodney

Post Edited (Yendor) : 12/13/2006 5:08:35 PM GMT

Bean

Stefano,
· Okay Ken was kind enough to send me a HM55B compass. Here is some SX/B code that will read the HM55B and set the variable "angle_MSB" to the direction.


· Use RUN->DEBUG->POLL to see the values change in the debugger.

Bean

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Cheap used 4-digit LED display with driver IC·www.hc4led.com

Low power SD Data Logger www.sddatalogger.com
SX-Video Display Modules www.sxvm.com
Stuff I'm selling on ebay http://search.ebay.com/_W0QQsassZhittconsultingQQhtZ-1

"USA Today has come out with a new survey - apparently, three out of every four people make up 75% of the population." - David Letterman

ellizard

HI Yendor.
Sorry for being late in the answer but the job took precedence.....

Thanks for the suggestion ........ to wich i too thinked, and discarded the idea after a bit of consideration.
The system I've in mind is composed of the HM55B module, the SX28 and a bunch of switches and LEDs for interface.
embedding in a umFPU would be for this use a bit like catching mosquitos with an aomic bomb.............


Anyway thanks
Stefano

ellizard

HI Bean.

Today after some days I could rejoin the forum, and I found that today.
And I've found another program for the BRads calculation of the X, Y data from the HM55B module,
what to say...... it's too gentle by You not let dropping a request in the forum until properly accomplished........

I'll let you know about the developments.................


For now Thanks

Stefano