I'm Attilio. I'm building an bioimpedance analyzer to monitor the impact of oedema on recovery after major abdominal surgery.
I bought AD5933 eval board but I need also of a analog front end board to connect the AD5933 at the skin.
Does anyone know if there is a card that is already built? help me please.
Unfortunately we do not have a Circuit From The Lab board on this as of yet. Please see attached a figure for a typical configuration that could be used. Care must obviously be taken in choosing RC values and levels of pk-pk so that the output is IEC standard compliant and meets the Cardiac Floating (CF) and/or Bodily Floating requirements.
Please refer to the AN-847 for an apps note on measuring a grounded impedance with an AD5933 + Instrumentation amplifier.
Hello, LiamR I hope you are doing well. I have implemented this circuit that you have mentioned above but after this, I cannot measure the unknown impedance accurately. Do we need to change our code according to this circuit?, if Yes then, What should I change in my code?
While the figure above shows the typical and straightforward implementation of AD5933 for bioimpedance application, there are other ways or configurations that will yield better accuracy.
I would suggest to implement voltage controlled voltage source at the output of AD5933 so the current through the unknown impedance will be constant across frequency and meeting safety norms will be easier. it will also help you eliminate errors on the wire and electrodes.
Did you perform calibration before measuring the unknown impedance?
Thanks, isantos for your reply. Do you mean to implement a circuit like this?
Yes, I am doing calibration before measuring the unknown impedance. By using the AFE mentioned below I can measure impedance from 47 Ohm to 1MOhm in the frequency range of (1Hz - 100kHz), but, in this case, the current is depended on load. For measuring the impedance of biological tissue we need the output current 1micro Amp at the load that's why I am trying to implement another technique.
I implemented LiamR suggested circuit like this, but it's not working, for example if I connect 1 kOhm resistor at the output for calibration and then measure 2 Kohm resistor. this circuit is giving wrong output impedance.
The AD5933 is quiet an old part. Just this year we released a follow on part the AD5940. This part is designed to carry out bio-impedance measurements. Refer to AN-1557 for details on some applications. We have an evaluation board available, EVAL-AD5940BIOZ, designed for bio-electric applications including BIA, EDA and ECG. User guide is here