Where do the electrodes go?

Hi,

Please find my response for your questions below :

1. The AFE has totally 8 - channels to connect your electrodes. Based on your need , you can choose any of the AFE pins. If you choose the channels AFE4 and the AFE3. The electrodes need to be connected between the jumper pins LK3 1 and LK3 2 and short the resistors R3 and R4 and install the jumpers LK11 and LK4.

Please note this is one of the method of hooking up a sensor electrodes. You can do this sereval ways. You need the ensure that the sensor electrodes are connected across the AFE channels.Here,you have the sensor electrodes across the AFE channels 3 and 4.You need to select the AFE channels accordingly in EKSP software.

2.In the 4-wire Bio-configuration, the IN-AMP_P and IN-AMP_N are connected to an IN-AMP to measure the voltage across the sensor and the AFE8 and AFE7 are connected to the AFE DAC  and TIA accordingly.

Please refer to the ADuCM350 user guide for better understanding of the AFE section.I am attaching a snapshot for your better understanding of the sensor hook-up in 4-wire mode.

3. AFE has only 8 channels to measure the sensor impedance and you need at-least two channels for each impedance measurement. If you electrodes can share the common mode current , you use one channel for the negative electrodes and the connect seven channels for the seven positive electrodes and then do the impedance measurement according to the SWITCH Matrix selection. Please refer to the SWITCH Matrix block of ADuCM350 of user guide for more details.

Hope this helps.

Thanks

Balaji

Hi Balaji,

Regarding your answer to Q3, I presume you were talking about 2-wire systems. With 4-wire systems, external in-amps are required. In a multi-electrodes 4-wire configuration, is it OK to connect several in-amps in parellel to the TIA_I pin of ADuCM350?

In the other hand, what if I need to reverse the DAC output by configuring the switch matrix (i.e.: not physically swap the electrodes)? In this case, will the in-amp and the TIA part work correctly?

Thanks and best regards,

Yervant

Hi,

1. I can run the supplied firmware without error, but when I run the EKSP on either the two wire or the 4 wire configuration I continue to get errors.I tried your answer to 1, and I will repeatedly get a UART HANDSHAKING ERROR once I've plugged in the electrodes, without them I do not get any such error(yet nor am I making any useful measurement). Do you have any supplied photo diagrams of your wiring set up or any ideas how to mitigate the UART HANDSHAKING ERROR?

Balaji : While the EKSP was tested on different versions of Windows (W7 32&64, W8 32&64), we have had reports that errors like what you describe occur. We believe that this may be a driver conflict issue on windows, but this has not been confirmed.we recommend that you download the Software Development Kit (SDK) and use the examples here to make your measurements. There are a number of different measurement examples available for you to use as a reference.

Please refer to the discussion here :ADuCM350 FAQ Evaluation Kit Software Platform .for more details.

2). Also, I've looked through the documentation, and realize that LK numbers refer to AFE numbers but would love to see a photographic wiring diagram of the ideal 4 electrode set up. I'm still having trouble getting this going. I can run the firmware, but when I run the EKSP I get:

Balaji : I have shown simple 4-wire connection using switch MUX schematics.Please find that below

3.'the value you have entered translates to an unsigned DAC code of 2045 which is outside the recommended limit of 1792 LSB's.

Balaji : What is the DAC output you are progarmming.  The  allowed range is +/- 600 mVp . If you program beyond this, you may get this error.

3. Just to confirm is that AD8266 an extra circuit that should be set up along side this daughterboard, or is it included on the 4-wire bio isolation board(is AD8266 U3)? Should I calculate Rcal and Rtia or can it be autocalibrated from the onboard resistors on this board? I've been looking through the documentation, and see many suggested different set ups(high precision current application would be great), although it appears the EKSP version in the documentation appears different from the one I am running.  I have chosen the set up above as it matches pg 18/28 of UG688.

Balaji : AD8226 is in-built inside the BIo-Config Daughter itself.Please refer to the documentation folder for schematics.RCAL and RTIA values needs to be calculated based on your range of current measurement.Please refer to the applkication note "AN-1271 Optimizing the ADuCM350 for Impedance Conversion" application note under the documenation folder for calculating the RCAL and RTIA based on your application.

Please note that if you do not the dc-blocking capacitors in your electrodes path, there is no need for AD8226. You can just use the switch-mux board and config the AFE channels accordingly.

I suggest you go through the AFE section in ADuCM350 user guide once so that you can get a complete understanding of the ADuCM350 AFE.

Hope this helps.

Thanks

Balaji

I can run the supplied firmware without error, but when I run the EKSP on either the two wire or the 4 wire configuration I continue to get errors.

I tried your answer to 1, and I will repeatedly get a UART HANDSHAKING ERROR once I've plugged in the electrodes, without them I do not get any such error(yet nor am I making any useful measurement). Do you have any supplied photo diagrams of your wiring set up or any ideas how to mitigate the UART HANDSHAKING ERROR?

Q2). Also, I've looked through the documentation, and realize that LK numbers refer to AFE numbers but would love to see a photographic wiring diagram of the ideal 4 electrode set up. I'm still having trouble getting this going. I can run the firmware, but when I run the EKSP I get:

'the value you have entered translates to an unsigned DAC code of 2045 which is outside the recommended limit of 1792 LSB's.

I desire to use it in a high precision current meter application, and have attached an image of the set up I am using.

Just to confirm is that AD8266 an extra circuit that should be set up along side this daughterboard, or is it included on the 4-wire bio isolation board(is AD8266 U3)? Should I calculate Rcal and Rtia or can it be autocalibrated from the onboard resistors on this board? I've been looking through the documentation, and see many suggested different set ups(high precision current application would be great), although it appears the EKSP version in the documentation appears different from the one I am running.  I have chosen the set up above as it matches pg 18/28 of UG688.

Thanks. I can get reasonable looking numbers on initial inspection of running the example code through IAR workbench. I was just keen to use the EKSP software and although it appears to connect to the COM port and run, I cannot receive any information.

When I get the bio-isolated board error(I do want to use the isolated board in 4 electrode mode ideally)  it is based on whatever the EKSP is sending and receiving. I can receive a magnitude and phase from the SDK example, just not through the EKSP.

I would love to use the EKSP as it would answer a range of questions quickly, if it worked on my computer(Windows 7 Home Premium SP1).

Thanks for all your help. 

Hi Yervant,

Please find my response below :

1.In a 4-wire , if you can allow DC into your sensor then you do not need the bio-config board and the in--amp. The Bio-cong board uses DC blocking capacitors in series with your sensors so that only AC is passed to the sensors. Based on your requirement you can select which one you need.Please refer to the FAQ

1 Bioimpedance Measurement Using ADuCM350

2 4Wire-Isolated-Bioimpedance ADuCM350 Connections To Sensor

for more details

2.DAC output is a bipolar output with a outpuyt voltage swing +/- 600 mVp.so you can set negative voltage across the sensor without chaning its electrodes.

Please refer to this FAQ AFE Transmit Stage for more details.

I suggest you to reply to the latest thread for easier access. I could not find out your query earlier.

Thanks

Balaji