Offset to variable howto ?

[RFsolution]

Hi all

I have the following problem

I read an ADC 10bit but would like to add an offset and keep the 10bit resolution

When the ADC value is smaller than the offset value I got a wrong indication on the LCD
substraction is going negative
any idea how i can solve this ?

eaxample:
offset: 200
if ADC = 512 - offset = 312 => no problem
if ADC = 180 - offset = -20 => wrong value

So i would like to keep the 10bit resolution but just shift it with the offset value ?


Thanks

[skimask]

See {I} {S} DEC {1..10} in the LCDOUT (and others) section of the manual.

[Jerson]

I read an ADC 10bit but would like to add an offset and keep the 10bit resolution
eaxample:
offset: 200
if ADC = 512 - offset = 312 => no problem
if ADC = 180 - offset = -20 => wrong value

This is not addition !!

JF

[RFsolution]

Ok you are right it is not addition but I mean

the 10 bits 1024 represents a position from a potmeter
in order not to change the fysical position i would like to add or substract an offset
but finnaly need to keep the 10bit resolution for further calculation
But I dont now how to do that

any help welcome

[Jerson]

Ok, I think I understand it now. You want to move the physical position of the pot in code.
You will be able to offset the reading. But the part that you've discarded due to the offset will be lost, so you cannot expect the full 10bits once you do this.

JF

[Acetronics2]

Ok you are right it is not addition but I mean

the 10 bits 1024 represents a position from a potmeter
in order not to change the fysical position i would like to add or substract an offset
but finnaly need to keep the 10bit resolution for further calculation
But I dont now how to do that

any help welcome

Hi, RF

Could you be more precise about what you want to do ...

The physical position of WHAT ???

i.e. read a pot with ADC , and from this reading show the pot angle, then place a servomotor's arm ... or what ???

Skimask's answer is one of the numerous possibilities ... consider it !!!

Alain

[RFsolution]

Hi Alain and others

Well I read a potmeter or other position encoder which is 10bit for full resolution
or equal to 1 single turn

Later I will convert this to Degrees (which is no problem)
But i would like to keep the maximum resolution to 10bit
but shift in the software the actual position instead of moving the potmeter mechanicaly

example

0 deg = 0V, 5V = to 360 (1024) or 10bit

imagine that the true 0 degree is at a value of 120 (decimal) and I dont want to move
the mechanical position of the potmeter but would like to see 0 as a decimal value
SO i would like to implement an offset of 120 decimal
whitout touching the 1024 10bit resolution for 1 revolution

I hope this is more clear

Walter

[Melanie]

So why not ADD an offset of 120 (using your example)...

That way zero will be in reality -120, 120 will be zero, and 240 is actually +120 ???

This way you will never go below zero, because zero is your REAL reference point, and your offset value is actually your mechanical zero.

Simple maths prior to displaying the figures will have it display whatever you want it to display.