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Strange Impedance Readings across PmodIA SMA Connectors


amekhanik

Question

Hello,

I am currently working on a project that uses the pmodIA and an Arduino (I am using a version of the code provided here: https://github.com/analogdevicesinc/no-OS/blob/master/drivers/AD5933/AD5933.c) and it is giving me strange impedance readings when I am running a sweep. It reads the calibration resistor really well but any other impedance, is really off (for example, I calibrate it using a 12K ohm resistor and it gives good readings for that value, but then any value higher than ~30K ohms, including open air, it returns as ~20K). 

I ended up grabbing a DMM and measuring the impedance across the connectors and interestingly, I found that when there is nothing connected in between them, the DMM reads ~5 ohms. So instead of there being an open circuit, like there theoretically should be when nothing is connected to the SMAs, there's actually effectively a short.

I thought that maybe this was some error with an individual board but I actually have a second one available and it reads the exact same impedance.

I am powering the board with 3.3V from my Arduino and the SEL pin is connected to VCC. Is there something painfully obvious that I am missing here?

Any help will be greatly appreciated!

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Hi @amekhanik,

Welcome to the forums! Here is a forum thread where a community member was able to get all of the functions working correctly. They also posted some helpful setup and usage hints as well as their code(unverified). I haven't worked with the PmodIA but I do know that there are specific calibration ranges in reference to impedance that the community member goes through as well.

cheers,

Jon

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