Calibrating AD5933 with Arduino

Question

Hi, 
 I am trying to interface the ad5933 with an arduino. Using the arduino I2C library, I am able to communicate with the ic, read temperature measurements, and program registers and initiate a frequency sweep. I have probed the excitation voltage and I am certain it corresponds with the programmed frequency and amplitude. However, when attempting to calibrate, the values the real and imaginary register values are off and the gain factor is off. I have used the suggested set up in the datasheet with a ZCal=200K and RFB=200K. Yet, the computed gain factor is about 256*10^-12, compared to the 515.8*10^12 in the datasheet. I know my gain factor doesnt need not be the same as the datasheet's but it should be similar at least. And with the current gain factor i'm getting, all test measurements within the range of the Zcal (Zmin - Zmax), are all wrong. I've attached my code herein. Kindly let me know if I'm doing something wrong or missing something. Thanks.

Marvin007 · Accepted Answer

Hi. I took a quick look at your code. I think when you send any value to Control Register 0x80, you need to 'AND' your new values with the values of D10/9/8 (Output voltage / PGA gain) to ensure the voltage and PGA gain are retained. If D10/D9/D8 are 0/0/0 then the output voltage is 2V and Gain x5. I assume you are seeing 2V.)

Snorlax · Answer

Perhaps all you need to do is adding I2C-controlled MUX and DEMUX or maybe just a switch array to your PmodIA. You can look at CN0349 schematic, ignore the U4 and U5, hook up SCL and SDA where designated and use U1 to connect to the test points. If the impedance range you are after are known, there is no need to switch between RFBs and RCALs, so all the switches can be utilized for your purposes.

Marvin007 · Answer

No probs. If it helps, here is a crude cheat-sheet I made for Control Register values (cites values as decimals). PDF and ODT (editable in Open Office) formats.

Marvin007 · Answer

Yes, sorry. it is bit-OR. My puny human brain got confused with the decimal addition I do in my code to get there. 
 As an aside, the chip's documentation included sample Visual Basic code. It had 2 types of "send data to the AD5933" routines. The most important one of those two, that sends to the Command Register, didn't contain full code. It took me a while to figure out why sending to those registers was different.....!

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Calibrating AD5933 with Arduino

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