Post Go back to editing

AD7793 output clamped to all zeros

Hey guys. 

I'm trying to include analog devices CN0326  pH-measuring circuit in an already existing measuring circuit controlled by an MSP430. 
For now, I have removed the isolator (ADum5401) because it rendered my LED display in an unpowered state. But this shouldnt affect any signals, since it only isolates between two digital areas. 

Anyhow, the problem at hand is, that the adc only outputs zeroes. 
I have solid SPI communication with the chip, and I can update and read from registers without any issues. I'm running on a very low bus-speed just to make sure my problems aren't SPI related (allthough I haven't ruled that out 100% yet). 

I start my software like so: 

Read ID register (I get the correct value) 

Internal fullscale calibration 

Internal zeroscale calibration

Set the mode register (Idle mode, 64kHz internal clk and 4.17Hz update rate). 

Set the config register (bipolar, Gain 1, buffered mode, ch1)   

I read both mode and config register back, and the correct values are stored. 

Then a lot of other stuff happens (regarding the other circuit) and when its time to convert, I change the mode reg to a single conversion, the config register to the fitting channel (Ch1 for pH, Ch2 for temperature). 

I'm supposed to measure ph in a -420 mV to 420mV span, but right now, I have tried every kind of voltage and configuration and I still can't get a conversion. 

I might not have configured it correctly even once. At this point I kinda blinded myself by trying so many different things. 

So for a +-420 mV range, how should i configure the adc with bias voltages, references etc etc. 

If you need any more info, please let me know. 

Parents
  • Hi,

    Circuit diagram of your entire system is also needed to check whether there is something wrong with hardware setup. CN0326 evaluation board was designed to have an external bias voltage of 1.05V and uses it also as the external reference voltage for the +/-490mV signal from PH probe. Thus, you don't need to enable the internal bias voltage and you have to configure the ADC with external reference in the configuration register. The PH sensor also use channel 0 so you have to select channel 0. May I know exactly the value of your configuration register?

    If you think you have configured the ADC with the above details and you still not getting data conversions. Can you stop reading back the conversions, set the ADC in continuous conversion and just monitor the DOUT/RDY pin to determine if it is pulsing at the selected output data rate? Please use OSC to monitor the DOUT/RDY pin as well as the SPI interface and show the waveform to us for further analysis. 

    Thanks,

    Jelelnie

Reply
  • Hi,

    Circuit diagram of your entire system is also needed to check whether there is something wrong with hardware setup. CN0326 evaluation board was designed to have an external bias voltage of 1.05V and uses it also as the external reference voltage for the +/-490mV signal from PH probe. Thus, you don't need to enable the internal bias voltage and you have to configure the ADC with external reference in the configuration register. The PH sensor also use channel 0 so you have to select channel 0. May I know exactly the value of your configuration register?

    If you think you have configured the ADC with the above details and you still not getting data conversions. Can you stop reading back the conversions, set the ADC in continuous conversion and just monitor the DOUT/RDY pin to determine if it is pulsing at the selected output data rate? Please use OSC to monitor the DOUT/RDY pin as well as the SPI interface and show the waveform to us for further analysis. 

    Thanks,

    Jelelnie

Children
No Data