Multiplexer / Demultiplexer with Labview and the Elvis Board

[Mathieu33800]

Hello.

I am a french student in England for a summer internship and I am working on a prototype of Electrical Capacitance Tomography (ECT). Indeed I am developing all the electronics of this system with the help of the Elvis Board and Labview. My actual task is to design a multiplexer/demultiplexer I need to supply my sensors and collect data from them on Labview.

My system have 12 sensors which are electrodes and my aim is to calculate the value of the capacitance between two electrodes. I supply one of these electrodes by a positive voltage and the others by the ground and I have to find the capacitance between the electrode supplied by a positive voltage and each one supplied by the ground. So I will use a demultiplexer to supply all the electrodes in a specific order with a lookup table on Labview; with the digital output and the DAQ (Input) assistant it will be okay I think. In attachment I put a scheme of a system which permit to convert the value of this capacitance in a sine. In this scheme the capacitance of 150fF (on the left) is the one between two electrodes, so the crosspoint with the other capacitances is where I want to connect one of my electrodes and the other extremity of the capacitance of 150fF at a second electrode. But I want to choose what electrodes connect to my system, and it is the purpose of a multiplexer (here I need two of them).

My problem is the next:

How to design a multiplexer (probably commanded by a look up table) on Labview, using 12 different signals (voltage) from the Elvis Board? Because with the DAQ (Output) Assistant I can recover the 12 signals (if I find 12 ports for this) but after I don't really know how to select such or such signal according to a precise lookup table or timing I don't know. Because I know the basics in Labview and a little more now but this seems very complex.

I hope I explained well my issue and thank you in advance for yours answers. Just a little advice could be the difference.

Gauquelin Mathieu

Student in Electronical Engineering School in France

[apok]

you can use a 4-16 line decoder to a 3 x cmos quad bilateral switch and common the output. write 4 digital lines to each decoder to control what analog switch to output.

[Mathieu33800]

Thank you for your fast answer. I will see if I can do something like this.

Best regards.

Gauquelin Mathieu

[AnalogKid2DigitalMan]

fF =  femtoFarads?

If so, you are going to have issues trying to measure in this realm. You have to follow strict practices and guidlines in wiring, layout, circuitry, fixturing, and measurement methodology to resolve such minute quantities. Such instrumentation is typically quite costly by itself.

This white paper is just touching the surface:

http://www.ni.com/white-paper/8505/en/

-AK2DM

[Mathieu33800]

I fix my problem.

So thank you for your help 😄

Best regards.

GAUQUELIN Mathieu

[Mancoba]

Hi everyone, I know this thread is a bit 10 years old, but I need to build something similar for my project to capture the switching behavior of the MOSFET. Can you maybe upload your program code, vi? Thanks in advance

[Mathieu33800]

Hello. I am sorry but it was 10 years ago and I don't have anymore the code, and no idea on how I did this because I didn't use anymore since this time the Elvis board. Good luck for your project 😉