Output of three DC signals for 8:1 multiplexor on NI ELVIS

[sflesh]

Hello,

I am a relatively new user of NI LabVIEW and NI ELVIS. As such, I do not have an extensive knowledge of the possibilities that are possible. For my project, I have a central electrode surrounded by 8 electrodes in a circle. I am using the impedance analyzer through ELVIS which only uses two wires at once. Thus, I would like to keep the central electrode constant and switch between the 8 outer electrodes until impedance has been measured in 8 different directions. To accomplish the switching, I bought an 8:1 multiplexer (data sheet attached), which needs three hi/lo signals to switch between each input. I have written the impedance analyzing portion of the code for two electrodes only and believe it won't be difficult to alter that for 8 electrodes using for loops. However, I have no idea how to write the code for switching the multiplexer. Right now I'm looking at NI DAQmx write VIs. So to begin my multitude of questions:

1) Is there any easier way to switch between electrodes using just the ELVIS? Also, I have access to multiple ELVIS machines if that is needed. 

2) If the multiplexer is needed, how can I send three DC signals to it, whose values can be altered after every iteration of the impedance analyzer to that a new electrode is used?

Sorry if this is a really vague description. Again, I am very new to LabVIEW. Any help would be much appreciated.

Thanks in advance,

Shane

[AnalogKid2DigitalMan]

The data sheet you attached is for a digital multiplexer, I have a hunch you would need an analog multiplexer to accomodate your signals. Akin to a CD4051:

http://www.oup.com/us/pdf/microcircuits/students/logic/CD4051-fair.pdf

What range of voltages do you need to switch? Note that analog multiplexers have an ON resistance of a few hundered ohms, do not know how this may affect your readings. You may have to revert to using relays with mechanical contacts.

Regardless, to switch the multiplexers you have to apply a binary pattern to the 3 select inputs. Not familiar with teh ELVIS platform hardware. In LabVIEW, search the examples Write Dig Port.vi, you would write hex 00 to 07 to change states on the three lower bits.

-AK2DM

[ajmartin]

http://forums.ni.com/t5/Academic-Hardware-Products-NI/bd-p/10

You may also want to ask ELVIS specific questions over on the ELVIS board., Link above

Alan

[sflesh]

Thank you both very much. I will look into those suggestions.

-Shane