Assistance Required for EIT Boundary Voltage Signal Processing and Frame Rate Improvement

[popular1119]

Hi Aaron,

I hope this message finds you well. I have a couple of technical questions regarding electrical impedance tomography (EIT) that I hope you can help with.

First, after the boundary voltage analog signal is selected through the multiplexer and amplified, it is sent to the analog-to-digital converter (ADC). Is there any special processing, aside from filtering, that needs to be done to the boundary voltage analog signal before converting it to a digital signal? Or can we directly convert the analog signal to a digital signal and then send it to the microcontroller for further conversion back to an analog signal without any special processing?

Additionally, I am looking to improve the acquisition rate to around 100 frames per second. Could you please advise on the best approach to achieve this?

Thank you very much for your help!

Best regards, Peng Piao

[RonAaron61]

Hi Peng Piao,

Hmm, I’m assuming that you want to read the Max/rms voltage, if so based on my previous project I think you should check the capability of your ADC first because if you directly input an analog AC signal into the ADC it may destroy the module, because the ADC may not be capable of reading a negative voltage, and even if the ADC can read negative voltage I think the readout may fluctuate between the max voltage and min voltage (assumed the signal is an AC signal). I think you can change the AC signal to a DC signal first then connect it to your ADC.

As for the acquisition rate, I also don't really know about this, but I think it is related to the controller's processing speed and how well/optimized the code is written.

Hope this help

Best regards, Aaron

[popular1119]

Aaron,

I'm not sure why, but the sine wave signal output from my AD9833 measures at an amplitude of 6V. I tried using the AD8421 and the programmable AD5270 to adjust the amplitude, but it had no effect and instead caused the waveform to become distorted.

Thanks!

Peng Piao

[popular1119]

The first one is the waveform directly output by AD9833, and the second photo is after adjustment.

[RonAaron61]

Hi Peng Piao,

Hmm, that's interesting, from what I read the output of AD9833 usually maxs at around 600mV, isn't the sine wave around 2.12Vpp in the image?, and so the problem is when you want to change the amplitude from the AD9833 it becomes distorted. I assumed you connected the output of AD9833 directly into AD8421 (which is an instrument amplifier) and controlled the gain using AD5270 (is it a digital potentiometer?). I never use AD8421 but I think it is similar to what I used before which is AD620. Do you connect the output of AD9833 to the Positive input of AD8421 and the Negative input & REF to GND? or do you have another configuration? because an Instrument amplifier amplifies the difference between the negative and positive input. Or maybe try adding a buffer between the output of AD9833 and AD8421 (?) another alternative is using a non-inverting amplifier to amplify the signal

Aaron

[popular1119]

Hi Aaron，

I checked the relevant information and found that the output of AD9833 is between 0.4~0.6V. I don’t know why it is so high here.

Peng Piao