calculation help for digital to analog converter

garoken · Jul 28, 2013

hi i am now studying a course right but there is a few question i want to ask
1st: say you are given -5 to 10 v output and need to be able to specify the voltage of within 50mv
how do i find resolution, accuracy and bits the converter will need
2nd: an object is moving at 40khz freq. how do i find the frequency the analog unit to the sample at???

because i am not very sure about the formula

iant · Jul 28, 2013

Analogue works within a "Range"
you have been given a range -5 to +10
ignore the -/+ look at the total = 15
now it is a simple calculation.
2.
what is frequency
Khz - Thousand Hertz
1 HZ = 1 cyle per second

welcome to the site

garoken · Jul 28, 2013

ya thanks a lot but as for the formula so far i only found resolution which 2n which is 2 to the power of how many bits but so far i am still lost about the accuracy and bits and for the 2nd does it mean i take 40 x 1000 since 1 khz = 1000hz??? ya i am a beginner at this

iant · Jul 28, 2013

2. 40,000 Hz or 40 thousand cycles per second

the formula 2n is number of bits including 0
the decimal system is 0~9
Binary is 0~1
so 2n = 2 x 1 = 2 bits (that is not 2)
But
2^3 = 2x 2 x 2 = 8
or 1000 (thats actually 8)
the correct formula is
2n - 1 for the binary maximum
2 x 2 x 2 - 1 = 7
OR 0~7 (111)
this gets confusing doesnt it.

your answer is a matter of how many bits is needed for each bit to represent 50mV
how many 50mV's are in 15v
keep calculating
your turn

iant · Jul 28, 2013

does this look close
100101100
there is a trap

iant · Jul 28, 2013

you can always have more bits
if you have 3 bits
you can only show 7 cant you?

balash · Jul 28, 2013

iant said:
Analogue works within a "Range"
you have been given a range -5 to +10
ignore the -/+ look at the total = 15
now it is a simple calculation.

Hmm, as bipolar converters use 1 bit for sign, i'd say that total number of bits for resolution would be calculated for range 0-max(abs(a),abs(b)) where a = max negative value, and b = max positive value.

which in this case would be 0-max(abs(-5),abs(10)) = 0-10V
so the converter would need to have resolution for 0-10V in step of 50mV plus 1 bit for sign

Peter Nachtwey · Jul 28, 2013

1. This should be intuitively obvious. The question is a little strange because though.
2. The answer to this one is not but a web search will provide the answer faster than asking anybody.

I have a feeling that the answer I would give for #1 would be graded wrong because the instructor would not take into account the practical aspects.

iant · Jul 28, 2013

Balash
It may seem hard but it is not
When someone is learning. I will not give you the answer. You will not learn.
My first comment. Ignore the +\- sign has not changed
Do not include it
It is 2:30 am Monday morning. Good night all.

balash · Jul 28, 2013

iant said:
Balash
It may seem hard but it is not
When someone is learning. I will not give you the answer. You will not learn.
It is 2:30 am Monday morning. Good night all.

Agree with learning.

Good night.

P.S. it's 7 pm hot sunday evening here...

garoken · Jul 28, 2013

so for the 1st one the best formula i use is 50 divided by 15 which equals to 3.333333333 then i use 2 to the power of 3 which is equals to 8 but as iant said they are only 7 in a binary so i minus by 1 which is equals to 128 bits??? because if i use to the power of 8 it will be 256 and is the formula for accuracy is it 10-5 over 2(128) or 7????

maxketcham · Jul 28, 2013

Garoken look at this web site, you need to be able to understand bianary to be able to do this type of work, and this page explains bits in an analog converter

http://www.facstaff.bucknell.edu/mastascu/elessonsHTML/Interfaces/ConvAD.html

you may also want to bookmark this page

http://www.facstaff.bucknell.edu/mastascu/elessonsHTML/TOC_BitsBytes.html

garoken · Jul 28, 2013

so i found the resolution is actually outputrange divided by 2^n i have the output range but i am missing the bits cause i am not very sure what is the formula and is accuracy same as maximum quantization error????

iant · Jul 29, 2013

50 mv = 0.05v
15.000 v
15/.05= 300
binary of 300 is the value i posted above
count the numbet of bits used = 9

total accuracey is 2^9 bits
or
111111111
or 511
or 0~511
(512 bits)

iant · Jul 29, 2013

:doh:Let me try that again
now divide 15 by 511 and your accuracey shows
0.02935 - this is the value of each bit in Volts
well within the requested 50mv

calculation help for digital to analog converter

garoken

Member

iant

Lifetime Supporting Member + Moderator

garoken

Member

iant

Lifetime Supporting Member + Moderator

iant

Lifetime Supporting Member + Moderator

iant

Lifetime Supporting Member + Moderator

balash

Member

Peter Nachtwey

Member

iant

Lifetime Supporting Member + Moderator

balash

Member

garoken

Member

maxketcham

Lifetime Supporting Member

garoken

Member

iant

Lifetime Supporting Member + Moderator

iant

Lifetime Supporting Member + Moderator

Similar Topics