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9v 18channel mv output divider

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lark68

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Hi Guys and Gals i'm new to all this electronic stuff and this maybe a simple question....but i would like some help if I may ask.

ok here is what i need to build.

i would like to make a interface to a Data Acquisition Unit that will provide a stepping mv source to the DAU for addressing checks.

I was thinking of using a 9v battery as a voltage source (could also be an external DC power supple source) and using a bank of resistors (could also be variable resistors) to divide the voltage over 18 channels to a 37 pin cannon type connector. also there is a requirement to be able to induce a 30V peak CMV at random while the other lines are floating.

can some one advise me on how i can build this interface box...I have no idea. also is there a way to make this programmable ?

best regards
Carl
 

MikeMl

Well-Known Member
Most Helpful Member
Something like this?
 

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lark68

New Member
thank you for you sketch...yes i guess something of that type...althought when i said a 30v peak at random i ment that any one channel could be and will be subjected to that CMV. So i assume that their should be a switch of some kind to switch the CMV to a particular channel.1-18.

What value of resistors would i use to have the output for the 1-18 channels in millivolt ranges.

regards
Carl
 

MikeMl

Well-Known Member
Most Helpful Member
thank you for you sketch...yes i guess something of that type...althought when i said a 30v peak at random i ment that any one channel could be and will be subjected to that CMV. So i assume that their should be a switch of some kind to switch the CMV to a particular channel.1-18.
Do you care that if you are reading a particular A/D input that the neighboring channels are simultaneously subjected to the common mode signal? With my proposed sketch, if you keep sampling a given channel, you should keep getting the same value regardless if the CMV is high or low. Set the 555 period so that you get like 50 A/D readings with the CMV low, and then 50 more with the CMV high. A histogram of the 100 readings would tell you if the CMV is affecting the readings.

What value of resistors would i use to have the output for the 1-18 channels in millivolt ranges.
Do you care what specific voltages are presented to the A/D inputs? If you just want them to be small, but monotonically increasing from Chan 1 to Chan 18, then just make a voltage divider consisting of say 1K resistors, with a final resistor to the positive end of the 9V battery will determine the voltage at channel 18. What is the input impedance of your A/D?
 
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