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AD5933 source code for AVR problem

Question asked by Walecki on Feb 7, 2014
Latest reply on Feb 26, 2014 by Walecki

HI,

 

I am trying to connect AD5933 with AVR microcontroller. My circuit is with AFE based on CN0217 with two ADG706 for calibration and feedback resistive networks.

 

I have problem to measure unknown impedance

My code is written according to datasheet and AN1252. I am a little bit of confused about correct program sequence- when I suppose to reset device, when to put it in stand by...

Lets say that I want to calibrate system with 10k and that Rfb is 10k, too. Later I want to measure Runknown=15k8 while Rfb remain the same- 10k.

 

1. CALIBRATING SEQUENCE

reset of device

program the start frequency

program delta_f

program number of increments

program the delay in the measurements

put device in stand-by??? (YES or NO)

program internal or external clock

initialize the system

perform sweep (one frequency, one point)

reset of device ??? (YES or NO) or put device in power down (YES or NO)

 

2. MEASURING SEQUENCE

put device in stand-by??? (YES or NO)

program internal or external clock

initialize the system

perform sweep (one frequency, one point)

reset of device ??? (YES or NO) or put device in power down (YES or NO)

 

or I should program all registers again?

 

My problem are incorrect measurements. Even if I disconnect resistors for Rfb and Rcal device perform the same results, values for R and I are the same so I assume that I did not program device correctly because obliviously it is not important if there is anything connected at the output or not- results are very close to defined value of Rcal in program.

 

I saw very similar problem in topic

 

http://ez.analog.com/thread/35345?start=0&tstart=0

 

but solution is not presented.

 

Please for comment and details regarding correct sequence- WHEN and WHY to reset/standby/power down?

 

Thanks,

John

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