Fast / low resolution A/D conversion
I'm considering an application which requires a 12F683 to perform a very fast A/D conversion - I don't need the full 10 bits the ADC normally supplies, probably just 4 bits of resolution is adequate. Reading the data sheet it says that if you terminate the conversion early (after say 5 TAD periods) nothing is stored. Is there a trick to get around this ?
Andrew
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How fast is enough? Do you detect some specific range/values, or just a threshold/single value?
Steve
It's not a bug, it's a random feature.
There's no problem, only learning opportunities.
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Hi, Andrew
Such use of ADCs are explained in the PIC Datasheets relevant chapters and Midrange Manual.
Good explanation also from the great " Bigonoff " ( a good asm teacher from Belgium ) - in French !
see Part 2 $19.6 ...
Alain
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Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
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IF there is the word "Problem" in your question ...
certainly the answer is " RTFM " or " RTFDataSheet " !!!
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Application is to detect a change in light intensity caused by an object passing in front of a confocally illuminated machine vision lens. It is battery powered so I want a low duty cycle illumination but fast enough to detect moving subjects.Originally Posted by mister_e
What i'm thinking is a cycle that runs:
1) Light on
2) Pause enough for sampling cap to charge
3) Start AD conversion
4) Light off
5) Interrupt on conversion complete and compare new intensity to old - GOTO event handler if significant change
6) Pause and loop
What I want is a total loop time of <1msec or less. I can run a TAD of 2usec so it would only be 22usec for the conversion which to be honest is probably way fast enough. It just seems wasteful to do a 10bit conversion when I only want 4 bits of data !
Andrew
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I couldn't find where to reduce the ADC resolution - can you be more explicit ?
Andrew
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You didn't search too much ...
23.7.1 Faster Conversion - Lower Resolution Trade-off
Alain
************************************************** ***********************
Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
************************************************** ***********************
IF there is the word "Problem" in your question ...
certainly the answer is " RTFM " or " RTFDataSheet " !!!
*****************************************
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Or perhaps not looking in the right place. It doesn't refer to it in the device datasheet but does in the midrange manual.
It's a pity you can't just stop the conversion after a certain number of bits.
Anyway, thanks for pointing me in the right direction.
Andrew
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aha ???
from the 16F87xa Datasheet ...To calculate the minimum acquisition time, TACQ, see
the PICmicro® Mid-Range MCU Family Reference
Manual (DS33023).
LOL ... Everything always in the Holy Datasheet plus PbP Manual ...
Ok, lots of reading ... but always useful !!!
Alain
************************************************** ***********************
Why insist on using 32 Bits when you're not even able to deal with the first 8 ones ??? ehhhhhh ...
************************************************** ***********************
IF there is the word "Problem" in your question ...
certainly the answer is " RTFM " or " RTFDataSheet " !!!
*****************************************
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