Decimal to Degrees mathematics help

[sayzer]

Keep in mind that "normal" potentiometers are NOT very linear. There are special types for positioning purposes.

Multi turn pots could be a good choice for positioning.
In 360 degree, with the help of some gears, the pot can turn 10 times.

Thus, Alain's math can have a better accuracy.

[ErnieM]

Some things to keep in mind here (and elsewhere too):

1) The max number from the analog conversion is 1023, which is the maximum number expressible with the 10 bits from the converter. SO, the maximum resolution you can get is 360/1023= .3519 degrees per bit

2) Converting from raw A2D number to degrees is simple, just (assuming max reading is 1023, and min is zero) A2Dreading x 360 / 1023. However, it is important to perform the calculation by doing the multiplication first, then the division. If you divide first you’ll loose a lot of precision (do you see why?) You’re working with integer numbers here, so the decimal parts get lost quickly. Alain has a good point when he scale up the reading, just be careful you do not overflow the variable; his use of 64 is the most you can scale this number up

Max scale factor = biggest word / biggest expected number = 65535 / 1023 = 64.0165… so use 64. PBP does have some facilities for handling double precision multiplicands (32 bit products), but that’s trouble to deal with.

[sayzer]

Lets make it simple.

Try my way first.

You will be surprised with the result.

[RFsolution]

Hey Guys

very suprised about the fast reply's , thanks to all !!!

I will give it a try this evening.

I agree that potmeters are not that linair, and I dont need the 0.3 deg
precision, but 8bit is not enough

Will try sayzers solution this evening, if it is not working i will post the code
for the specialists

Thanks agn

[sayzer]

....
if it is not working i will post the code for the specialists

You broke my heart !


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[RFsolution]

Hi

This is what I have but dont see any light in "my" tunnel

OSCCON = $60
DEFINE OSC 4
DEFINE adc_bits 10
DEFINE adc_clock 3
DEFINE adc_sampleus 50

adcresult VAR WORD
dummy var word
adcon1=%100000010
maxvalue var word
minvalue var word
scale var word
result_64 var word

init:
maxvalue = 64000 'this is 359,8 degrees
minvalue = 2200 ' this is equal to 0 degrees

loop:
gosub readadc
Scale = MaxValue - MinValue
dummy = (AdcResult - MinValue) * 64
dummy = dummy * 360
Result_64 = DIV32 Scale
SerOut 6,6,["adc=",#adcresult," scale=",#scale," dummy=",#dummy," res64=",result_64,10,13]
goto loop


readADC:
ADCIN 0, adcresult
return

[ErnieM]

OK, a lot of code, but no hint as to what is going wrong!

When getting up a new project, try to cut it into as many small slices as possible, get first to work, then move on to the next slice.



Slice 1: getting out debug info. Method: just post dummy data.

Slice 2: Read A2D. Method: read it, then output as debug info

Slice 3: Convert to degrees. Method: as discussed

[sayzer]

Hi

This is what I have but dont see any light in "my" tunnel

OSCCON = $60
DEFINE OSC 4
DEFINE adc_bits 10
DEFINE adc_clock 3
DEFINE adc_sampleus 50

adcresult VAR WORD
dummy var word
adcon1=%100000010
maxvalue var word
minvalue var word
scale var word
result_64 var word

init:
maxvalue = 64000 'this is 359,8 degrees
minvalue = 2200 ' this is equal to 0 degrees

.....

You have 10bits of res. Thus you need the result as right justified. But you have adcon1=%100000010 one extra 0 is typed here. So the result becomes as left justified. Thus you get your results as 64000 and 2200.

Change it to adcon1=%10000010. So you now have correct right justified setting.

Then check the readings again.



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