Hi-res software implemented ADC in 16Fxxx ?? Who knows how?

[Lucidan]

I'm looking for a way to make a 16-bit ADC, without using built-in ADC, since those have only 10-bit resolution.

Who can help me?

[SherpaDoug]

Pick your favorite chip company, Maxim, Analog Devices, National Semiconductor, Texas Instruments, etc. go to their web site and use their product selection wizards. Also check the CCS examples files.

Note Maxim (www.maximic.com) is very good about free samples!
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The search for better is endless. Instead simply find very good and get the job done.

[Lucidan]

Thanks, but i'm looking for a way to implement this in the PIC (software), with a minimum of external components needed.

[Franck26]

Hi Lucidan,
If you want to implement a software ADC, you will have to use a R/2R resistor network and an analog comparator (analog comparator are already implemented in some pic).
But there is no point to do it if you want a 16 bits ADC, because of the resitors tolerance: you will have something worse than 10 bits...

For a 16 bits ADC, the only (good) solution is to use anintegrated ADC, to have a good reference voltage and a good layout.

Good luck.

[kolio]

You can try with so called "dual slope adc" circuit. Slope ADCs are always slower, but more precise (depends on timer resolution). Check this link for some theory:
http://www.mines.edu/Academic/courses/physics/phgn317/lect11/sld008.htm
You'll need to build a circuit with several external components:an analog switch ,integrating opamp, constant current source, temperature-stable resistors and capacitors. The comparator is most probably available in PIC16 and the timer definitely :-) The hard part is signal conditioning at the input - you'll need some active filtering with an opamp if the measured signal is not battery voltage level for example, but the load cell of an electronic scales.
My first job 14 years ago was to build an electronic scales with dual integration circuit. But then I found Intersil ADC ICL71-something...

P.S. If your project is not educational or hobbi, better listen what Sherpa told you and purchase an ADC right now

[Guest]

Microchip has an application note AN700 that describes the following,

(text from Microchip.com)
This application note describes how to implement an Analog-to-Digital (A/D) Converter function using a member of the PIC16C6XX series of microcontrollers. Although these microcontrollers do not have a built-in A/D Converter like other controllers from Microchip, the comparator function, internal voltage reference and timers can be used to digitize an analog signal. Some of the standard PICmicros have a comparator module, consisting of two comparators, both of which can be connected to PORTA in a variety of configurations. The internal voltage reference divider can be used with the comparators to establish thresholds. Additionally, one of the comparator inputs can be configured to the RA2 port allowing for the use of an external voltage reference. By combining these elements, a first order modulator and first order filter can be designed, emulating the function of an analog-to-digital delta-sigma conversion. This method of conversion is quickly implemented in firmware with very few additional external components. Consequently, the cost of hardware implementation is minimal, particularly for such a high resolution converter solution. The input range is very flexible and adjusted with external resistors. Although this method is not particularly strong in terms of DC accuracy, it is well suited for ratiometic applications.

HTH - Steve H.

[SherpaDoug]

Read Microchip application note AN512. It tells how to build an A/D conversion mechanism with minimal hardware. It also describes the limitations of such a system and why you will never get 16 useful bits from it. AN512 is a good education about what can and can not be done by software.
_________________
The search for better is endless. Instead simply find very good and get the job done.