Beginner A/D Conversion Question
Alan B. Pearce email (remove spam text)
>> ... sensor outputs ... -3.6 and +3.6 volts.
>> I don't know how to handle the negative voltage with an A/D IC.
>> ... There's got to be a simple solution to this problem, ...
>Fortunately, there is.
>> I'm not looking for a complete solution, just some pointers to get me
>> going in the right direction.
>So - standard differential op amp / or summing opamp circuit will do what
>you want. A bit of Googling on that area will turn up something useful.
Personally I would look at an ADC that takes negative voltages. One I have
had contact with is the Linear Technology LT1414 which is 14 bits, but
parallel interface. Requires +5 and -5 supplies, and input range is +/-2.5V.
I am sure that if you go digging around the Linear Technology or Analog
Devices web sites you could find some 14 bit adc that have serial interface,
if this is more useful. A quick scan at LT indicates the LTC1858 might suit,
with SPI interface. Had a quick look at the data sheet, single 5V supply, 8
channel mux, various options for input ranges (0 to 5, 0 to 10, -5 to
+5, -10 to +10), also has 12 bit and 16 bit versions, 100ksps, but it is a
29 pin SSOP package. Looks like it can also be run as 4 differential inputs,
or a mix of differential and single ended. If that doesn't suit, check the
"related parts" table at the end of the data sheet.
Another nice thing about LT is they will sample with no questions asked. My
recent experience with AD is they kept following up, but it was an expensive
device I asked for (around US$30).
See also: www.piclist.com/techref/io/atod.htm?key=a%2Fd
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