8 bit adc

Discussion in 'The Projects Forum' started by texasbill, Jan 20, 2016.

  1. texasbill

    Thread Starter New Member

    Jan 20, 2016
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    I need to build a 10 volt in 8 bit adc converter anyone have any plans or advise?
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Why do you need to build one rather than simply buying one?
    Is this homework?
     
  3. Papabravo

    Expert

    Feb 24, 2006
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    I also don't understand the precise implications of needing to "build" one. These are available as single chips with all the bells and whistles. The analog IC designers have already done all of the building required.
     
  4. texasbill

    Thread Starter New Member

    Jan 20, 2016
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    no not homework, I have to build it for work. Our sensor is analog and the rest of the equipment is digital and analog replacments are not available any more. I was told that 8 bit ADCs 0 to 10 volts were not available either. If you have a part number i sure would appreciate it.
     
    Last edited: Jan 20, 2016
  5. Papabravo

    Expert

    Feb 24, 2006
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    Here is what I recommend. Build a gain of 1/2 voltage divider and buffer it with a single supply voltage follower. Run the 0-5V signal into the ADC of your choice. They can have parallel, SPI, or I2C interfaces. There are literally hundreds to choose from and it is hard to go wrong. Try creating an example schematic and we can go from there.

    http://www.mouser.com/ProductDetail/Maxim-Integrated/MAX11644EUA+/?qs=Bakm8ERcljqcrTtofIuJcQ==&gclid=CIjCsdnGuMoCFQotHwodVj0AYg
    http://www.mouser.com/ds/2/256/MAX11644-MAX11645-86103.pdf
     
    Last edited: Jan 20, 2016
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Rather than redesign the wheel buy most any micro controller that has a built in A2D and at least 10 pins. Write a small program that reads the input voltage and then outputs the top 8 bits on 8 I/O lines.

    Extra credit for adding a reference voltage.

    To use it in your device just add an appropriate divider at the input to scale the voltage down to what the micro can handle.

    A few other details such as what power you have available, accuracy, over range protection and the like would be needed to flesh out a complete design. Something like this would take a day or two for an experienced micro guy. Designing an A2D from scratch would certainly take longer and have an unpredictable outcome.

    Edit to add make that 11 pins or more.
     
    Last edited: Jan 20, 2016
  7. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Replacements for what? Sharing the original A/D manufacturer and p/n will save about 50 messages.

    Separate from that, any discussion about a replacement (part or circuit) needs a buttload of details about available power, speed, number of input channels, noise environment, source impedance, output data format,,,,,,.

    Finally, expand your search. 8-bit devices may not be available, but 10-bit and 12-bit devices are. The 12-bit AD7880 can be configured with an internal 2:1 attenuator, so it can handle 10 V signals with a 5 V supply. Texas Instruments has former National Semiconductor and Burr Brown 8 and 12 bit parts with direct ++/-10V inputs.

    ak
     
    Last edited: Jan 20, 2016
  8. texasbill

    Thread Starter New Member

    Jan 20, 2016
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  9. texasbill

    Thread Starter New Member

    Jan 20, 2016
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    Engineer gave me a Maxim MAX160CPN. He said it has to be 8 bit to interface our equipment to the computer and program we are running. I believe he chose this IC due to the fact that it is 10 volt input. I could probably use a voltage divider and would just be dividing 5 volts by 255 steps rather then 10. I mocked it up using a 555 set at 60 Hz on my breadboard and it worked but when I soldered it to a circuit board with a delta +15/-15,5volt power supply it is very unstable and doesn't appear to be sequencing properly. I take the -15 volt put it thru a voltage divider with a variable resistor to allow me to set the ref voltage and power everything else with the 5 volt. I'm wondering if the common comm between the -15 and the +5 volt supply is the culprit. When I benched it for the clock I used a stand alone freq generator. I put 8 LEDs on the outputs so I could see their state easily. When it worked all LEDs were off and at about 40 mv the first (lsb) would illuminate and it counted in binary right up to about 10 volts. Now all the LEDs flash from MSB to LSB and the proper one (at times and lsb wont start till 44mv)will appear brighter but still flashes. On the breadboard with the 555 it displays the flashing properties I haven't had the chance to use the function generator.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    Your discussion is very disjointed and it's hard to follow what you are doing. :confused:
    What's the function of the 555 in generating 60Hz?
    What are the ±15V supplies powering?
    Do you still have a problem?
     
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  11. texasbill

    Thread Starter New Member

    Jan 20, 2016
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    Yes im still having problems. Clock is for the adc clock input, -15 volt supply gets knocked down to -10 volts and is the ref voltage. 5v is for ic vdd
     
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