ADC module for mid range PIC uControllers

Discussion in 'The Projects Forum' started by ChrisChemist116, Jul 26, 2010.

  1. ChrisChemist116

    Thread Starter Active Member

    Mar 13, 2009
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    1
    Greetings to all

    I am trying to work with this pic -> PIC16F628A, but since this IC doesn't have a built in ADC module what should i do?:confused:

    Okay i know the best option would be to find a PIC which does include a built in ADC like PIC16F88, but how about if i want to skip this step and try to stay with the 628A?

    So, i came across this module ADC0804. However i dont know if such IC would be the best option for me?. This module can be rather old or maybe there are newer replacements.

    Any ideas? Are there any new ADC modules out there? :rolleyes:
     
  2. Markd77

    Senior Member

    Sep 7, 2009
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    I'm not sure why you would want to stick with the 628A. It isn't too hard to change the code to move to a 16F819 or 16F88. Unless you need more precision or speed than a built in one. You have to use more pins and more code to talk to an external ADC and the cost and board space would be higher.
     
  3. tom66

    Senior Member

    May 9, 2009
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  4. ChrisChemist116

    Thread Starter Active Member

    Mar 13, 2009
    78
    1
    Thanks for your comment. I know i may sound rather annoying to stay with what it can be a subtle caprice.

    i was attempting to ask an open question. Of course i understand that it can take more lines in the code and space in the board.

    But how about if we put all of the previous 'pros and cons' aside and just to make this question as a challenge for some people who want to experiment with new things?. regardless the cost and so on. whatever....

    And i do know its easy to change the code from one micro to another. Anyways your critics are welcomed, although not helpful ;)

    What you said about precision and speed its interesting. What is the highest resolution and speed i can find on external ADCs?

    Thanks for the answer. I wasn't even aware Microchip does manufacture external ADCs.

    I took time to see the list and all of them, seem to range between 10 to 13 bits in resolution and 1 to 8 channels on input, which is good for most of the things i do work with.

    But how about more precision or more channels? are there any better options than those provided? I dont know much about other brands.
     
  5. Markd77

    Senior Member

    Sep 7, 2009
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    I had a quick look at RS components and they have ADCs up to 24bit and up to 500MSPS. You could use fairly high speeds if you used a parallel one.
     
  6. tom66

    Senior Member

    May 9, 2009
    2,613
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    Microchip actually manufacture some delta-sigma (ΔƩ) ADCs up to 18-bit and 64,000 samples/second. This URL:

    http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en544175

    I'm not sure it can do 64,000 samples/sec at 18-bit. But it also has the option (from a quick read of the datasheet) for 24-bit 256x oversampling. Of course, this kind of oversampling comes at the cost of speed.

    For more channels, you can look at some of their other offerings, or use a simple 8-channel mux chip, something like a CD4051.
     
  7. sage.radachowsky

    Member

    May 11, 2010
    241
    38
    There are *all* kinds of ADCs out there. Some can sample at MHz rates. Some are 24-bit.

    You have to balance speed, resolution, price, power usage, and other factors, and find what you need. Then do a few hours of searching on the spec sheets and choose the best one for your project, if it is important.

    Typical units in the low-cost category can sample 10K to 100K Hz at 10 to 16 bits. Some ultra low power chips can only sample at 200 Hz but run on only a few microAmps. Some expensive chips can sample 500 KHz at 16 bits, and use 300 mA...

    Analog Designs makes a lot of high accuracy expensive ones. Specialty ADCs are available for audio from them and other makers. Linear also makes a lot of high end ones.

    Texas Instruments makes general purpose and lower power ones. Microchip makes a lot of low power, lower end ADCs.

    I always use the ones in microcontrollers. I have never needed more than 12 bits so far... but you never know.
     
  8. ChrisChemist116

    Thread Starter Active Member

    Mar 13, 2009
    78
    1
    I have seen them as well. As i mentioned to my application 10 bit is just fine, and since my simpathy for the DIP package, overall its not so hard to find. To talk about speeds low sps is just fine as well (for now).

    Did you say Analog Designs?:confused: haven't you meant Analog Devices? They claim to be the world leader in signal processing.

    As i mentioned before, speaking to brands i am totally clueless. However i know that Intersil, Linear Technology, National Semiconductor, Cirrus Logic, NPX have been in the business for quite sometime. I can't tell which is better or which is the oldest or reliable. Maxim IC and Texas instruments also make ADC modules serial and SPI.

    From this post i had come to the conclusion that higher resolution seems to be 24 bits. Is that true?.

    I have seen 31 bits on this Texas Instruments chip -> ADS1282 from the data mentioned in the site tells applications range from Energy exploration, seismic monitoring to high accuracy instrumentation, perhaps medical equipment.

    Okay so, Is there any higher resolution beyond that point? 31 bits is the maximum we've reached with today's technology at a commercial level or at any level?:rolleyes:
     
  9. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
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    As a suggested exercise, try taking a 5 volt signal and dividing it by various powers of 2. You may find that anything beyond 16 bits (65536, or 76 uV/bit) is just not very useful - or possible.
     
  10. ChrisChemist116

    Thread Starter Active Member

    Mar 13, 2009
    78
    1
    Okay let's see.


    So (considering exponentiation is ^) don't know if phpBB code is enhanced for mathematical operators. Whatever..
    • 2^2 would be 1.25 volt/bit
    • 2^4, 312.50 mV/bit
    • 2^8, 19.53 mV/bit
    • 2^10, 4.88 mV/bit
    • 2^12, 1.22 mv/bit
    • 2^14, 305.18 uV/bit
    • 2^16, 76.29 uV/bit
    • 2^24, 298.02 nV/bit
    • 2^31, 2.33 nV/bit
    And i believe the list would continue. But rather than being a fun;) excercise. My question has remained unanswered, is there any resolution beyond that value (31 bits)? Has been designed or created?.

    I know it can be unpractical, it might be impossible, and it may sound like to ignite a campfire with a flamethrower. But i am sure that there are applications that rely on ultra high resolution needs, like the ones mentioned such as medical, seismic instrumentation, space exploration, etc.:eek:

    Maybe anyone on such fields or related to those can answer my question. Dont know. :confused:At this point i remain clueless about it...
     
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