ADC Input Question

BigT

New to the Parallax forum, and allow me to set the stage about myself.

I am by no means an electronics engineer.

I do, however, possess an Associates Degree in Electronics, which, I obtained in August of 1984, and have never pulled upon that knowledge, being placed right after school, into a position not related to electronics.

Point being, I am in tune enough to understand any help that may be given me, through any questions I ask.

My love for electronics abounds, and I am getting back into the loop, and in so, am designing a project involving microcontrollers, and the project itself, is small enough that I have chosen to go with the Parallax line of microcontrollers, which I find a joy to work with.



For my project, I have chosen the BS1.

Why?

Quite frankly, I only need a few I/O pins, and the BS1 was more than enough for my requirements in this particular case.



But my question deals with Analog to Digital convertors.

I have done what I believe to be extensive research into ADC's, and their application to microcontrollers, such as in my case, the BS1.

Have even got the ADC0831 8 Bit ADC properly interfaced with the BS1, however, for my particular project, I need the resolution, (more digits to the right of the decimal point), found in a 12 Bit ADC, as I am tracking the Vacuum Analog voltage from a Freescale MPX5100DP Pressure/Vacuum Transducer:

http://cache.freescale.com/files/sensors/doc/data_sheet/MPX5100.pdf?pspll=1

The Freescale MPX5100DP Pressure/Vacuum Transducer has two interfacing ports found on its housing. Port One is used to measure pressure, and Port Two, to measure vacuum, which, is what my project involves, the detection of vacuum leakage.


I am aware that I will grab my Analog voltage from Pin 1 of the MPX5100DP, but that is not my question.


My question stems from a little bit of confusion on the part of Analog signal input on a 12 Bit ADC, versus that of an 8 Bit ADC.

Point being, on the ADC0831, you had (Vin+) as your Analog In. Easy enough.

But lets say on the LTC1298 12 Bit ADC:

http://www.parallax.com/Portals/0/Downloads/docs/prod/appkit/ltc1298.pdf

http://cds.linear.com/docs/Datasheet/128698fs.pdf

which seems to be a favorite/proven 12 Bit ADC for Parallax applications, you now have, what appears to me, to be, two Analog Inputs, (CH0), and (CH1).




My questions stand as:

I only need one Analog Input. Using the LTC1298, is there a "proper" procedure to use only one of the Analog inputs to read from the MPX5100DP?

Or, perhaps better to use the LTC1286, as the LTC1286 appears to use only one Analog In, Pin 2, (+IN)?

Or, as I had read in one of the Parallax forums, could the Microchip MCP3201:

http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en010531

be yet a better choice for my application?



I am sorry for the lengthy post, however i realize that a detailed, and descriptive posting is not only appreciated, but crucial in helping someone with their situation, as I would appreciate as much detail as possible if someone needed my help.

Thank you for your time,

BigT

Mike Green

Look at the AppKit documentation you posted ... on page 6. There's a description of the LTC1298 that mentions that it has two analog inputs and the BS1 program sends a selection code to it to designate which channel to use. If you only need one channel, you can just tie the other channel's input (CH1) to ground and always use the selection code for the 1st channel (oddSign = 0). You could also use a different ADC, but there's already tested sample code for using an LTC1298 with a BS1 ... why mess with a proven solution?