AD7730 interfacing with ATmega

ad7730

Hello All,

I have a little problem in interfacing with AD7730 EVA board from Analog devices.
Basically i connected the SPI lined to ATMega8.
I am able to read/write to any register.(which SPI polarity, timing is OK).
I try to calibrate AD7730 as below

1. Do HW reset
2. Write to filter register 0x800010
3. Write to DAC 0x00
4. write to mode register 0xA130 //int.full scale calib
5. wait for ready signal
6. write to mode register 0x8130 //int.zero scale calib
7. wait for ready signal

8. write 0x4130 //single conv
9. Wait for ready
10. read the data

i always get some junk data irrespective of input voltage from 0mv till 80mv
Ready signal goes low correctly!!!

i fed the signals to AIN1+, AIN1-
i fed 2.5V reference
i checked till the controller pin that the input voltage comes OK.
reference voltage to the pins are checked OK
i also try skipping steps 2 to 7 (skip calibration) but result doesn't change much
i also tried to change the channel pair, unipolar/bipolar, single / continuous conversion...but always wrong result(0x8Bxxxx).
i am feeding voltage through simple resister network.

Any kind of help will be appreciated.

Regards,
bhas_pp

ad7730 site:edaboard.com

this convertor is converting differential voltages, therefore you have to check that the voltages applied to AIN+ and AIN- pins are in the range Vref/2 - input range ... Vref/2 + input range if it's bipolar, and Vref/2 - input range/2 ... Vref/2 + input range/2 if it's unipolar. I have used this convertor and worked fine.

atmega interfacing

thanks for your help, now it works

hi, please for source code and schematic, I'm just beginer. Thx