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ADS1194: Facing lead off detection issue with chip ADS1194

Kameshwar Prasad
Prodigy 20 points
Part Number: ADS1194

Dear Sir,

In my project, interfacing ADS1194 chip for the 7 lead ECG recording.

I am facing issue regarding LeadOFF detection of Lead1(1-),Lead2(1+),Lead3(2-),Lead4(2+),Lead5(3-),Lead6(3+) and Lead7(RL).

I want to detect every lead status (Connected or Not Connected??).

Please see our schematic to interface 7 lead ecg cable for your reference.

Also see our register configuration as bellow.

unsigned char ADS1194RegVal[28] = {

//Write register opcode1
0x41,
//Write register opcode2
0x18,
//CONFIG1
0x05,     // Sampling Rate = 250       
//CONFIG2
0x22, 
//CONFIG3
0xDF,
//LOFF
0xef, 
//CH1SET (PGA gain = 6)
0x00,
//CH2SET (PGA gain = 6)
0x00,
//CH3SET (PGA gain = 6)
0x00,
//CH4SET (PGA gain = 6)
0x81, // Power down mode and i/p short
//CH5SET (PGA gain = 6)
0x81, // Power down mode and i/p short
//CH6SET (PGA gain = 6)
0x81, // Power down mode and i/p short
//CH7SET (PGA gain = 6)
0x81, // Power down mode and i/p short
//CH8SET (PGA gain = 6)
0x81, // Power down mode and i/p short
//RLDSENSP (default)
0x07,
//RLDSENSM (default)
0x07,
//LOFF_SENSP
0x07,
//LOFF_SENSM
0x07,
//LOFF_FLIP (default)
0x00,
//LOFF_STATP (Read only)
0x00,
//LOFF_STATM (Read only)
0x00,
//GPIO
0x00,
//PACE (default)
0x00,
//RESP (default)
0x00,
//CONFIG4
0x02, 
//WCT1
0x00,
//WCT2
0x00,
}; 

With above configuration and schematic ---- When we remove Lead1 then its status disconnect coming again reset and coming and again reset.

But we want as bellow

If connected then its status 0 - fixed

If disconnect then its status 1 - fixed.

What is the reason??

Please reply to us ASAP

RegardsECG ANALOG SECTION.pdf

Kameshwar Prasad

  • 0
    TI__Mastermind 19815 points

    Hi,

    When you say "status disconnect coming again reset and coming and again reset", are you saying it sometimes showing ON and sometimes showing OFF?

    ------------------------------------------------------------------------------------

    May I ask which Lead off detection method do you use? refer to datasheet page 56 a) DC Pull-Up/Pull-Down Resistors, or  b) DC Current Source, or AC Lead off?

    May I ask do you use RLD drive electrode? RLD drive plays an important role for Lead ON/OFF stability.

    Do you test with an ECG simulator or human subject?  It's suggested to test with an ECG simulator first.

    ---------------------------

    Once customer uses the RLD drive, developers&designers will need to search&adjust&tune the RLD_SENSN and RLD_SENSP switches, and Lead off threshold settings to a good combination settings according to/based on their peripheral circuits designs, product designs and electrodes/patches used, etc.

    That is the experiment&tests&data collection&analysis processes developers&designers need to go through before making decisions and highly designs and products dependent.

    Again, suggest to start with an ECG simulator to get familiar and understand the settings first, and then move on to other to repeat/iterate the similar processes.

    Thanks

  • 0 in reply to ChienChun Yang
    Prodigy 20 points

    Hello ChienChun Yang,

    Thanks for your reply.

    1. Yes lead shows OFF and after some time ON. Mean Toggling the lead off Bit when lead disconnect from the Simulator.

     When Particular Leads connected that time corresponding bit status are not toggling. This issue raise when we disconnect lead. 

    2. We are testing with Fluke Simulator ProSim8.

    3. We are using DC lead off We have shared Register configuration. Is it ok?? Config3 = 0xDF / 0xDE is same behavior.

    Regards

    Kameshwar Prasad

  • 0 in reply to Kameshwar Prasad
    TI__Mastermind 19815 points

    Hi,

    Thanks for letting me know that you are using ECG simulator for test.

    But, are you using DC resistor method or DC current method for lead off detection? datasheet page 56 a) DC Pull-Up/Pull-Down Resistors, or  b) DC Current Source.

    Also, there were several follow-up questions asked above, but not yet answered by the customer, e.g. RLD?

    ------------------------------

    Anyway,  as suggested in the previous reply -

    Once customer uses the RLD drive, developers&designers will need to search&adjust&tune the RLD_SENSN and RLD_SENSP switches, and Lead off threshold settings to a good combination settings according to/based on their peripheral circuits designs, product designs and electrodes/patches used, etc.

    That is the experiment&tests&data collection&analysis processes developers&designers need to go through before making decisions and highly designs and products dependent.

    Again, suggest to start with an ECG simulator to get familiar and understand the settings first, and then move on to other to repeat/iterate the similar processes.

    -------------

    Thanks

  • 0
    Prodigy 20 points

    Dear Sir,

    Sorry for the late reply. 

    1. Now when we disconnect any lead from Lead1 to Lead6 then it is working ok.

    2. But when we disconnect RL(Lead7) only. All other leads are already connected. In that scenario      RL- Lead status toggling. If we disconnect any other lead also then this lead and RL lead status      showing ok.

    3. I am doing sums of  CH1 (+), CH2(+) and CH3(+) by Mux and this is connects with RLD_IN. and rest in the schematic.

    This configuration is ok??

    CONFIG3-      0xCF  

    RLDSENSP -  0x07;
    RLDSENSN -  0x00;

    Regards

    Kameshwar Prasad

  • 0 in reply to Kameshwar Prasad
    TI__Mastermind 19815 points

    Hi,

    Let's troubleshoot and debug step by step.

    ---------------------------------------------

    Are you using DC resistor method or DC current method for lead off detection? datasheet page 56 a) DC Pull-Up/Pull-Down Resistors, or  b) DC Current Source?

    --------------------------------------

    Regarding to

    "1....." Sounds good.

    "2. But when we disconnect RL(Lead7) only. All other leads are already connected.
    In that scenario      RL- Lead status toggling. "   

    Which method do you use referring to datasheet page 57 - "two measurement procedures to determine the RLD electrode connection status using either
    a current
    or
    a voltage pull-down resistor, as shown in Figure 49."    ?

    And, depending on how/which method you use in above, e.g. if it's Voltage with pull up/down resistor, do you have resistors?

    As described in page 57-

    "The reference level of the comparator is set to determine the acceptable RLD impedance threshold."

    "The comparator thresholds are set by the same LOFF[7:5] bits used to set the thresholds for other negative inputs."

    So, you may want to play/adjust LOFF: Lead-Off Control Register's Bits[7:5] COMP_TH[2:0]: Lead-off comparator threshold.

    It could be possible that you need to set different threshold values for the RLD lead off detection.

    Thanks

  • 0 in reply to ChienChun Yang
    Prodigy 20 points

    Dear Sir,

    Thanks for your reply and support.

    1. Which method do you use referring to datasheet page 57 - "two measurement procedures to determine the RLD electrode connection status using either
    a current or a voltage pull-down resistor, as shown in Figure 49."    ?

    We are using --- as beloow

    a). Current Source mode lead OFF.  (Reg LOFF bit4 - 0)

    b). Lead OFF comparator Threshold - Positive Side - 70% and Negative side - 30%.

    c). Lead OFF current magnitude - 16nA.

    d). Lead OFF frequency - DC lead detection turned on.

    2. We have already share to you schematic of ADS1194 chip and its lead connection.

        As per schematic - RLDINV(Pin. No. 61), RLDOUT(Pin. No.-63) and RLDIN(Pin. No.-62) is ok?? I have use C35- 1.5nF and R55-1M.

    Regards

    Kameshwar Prasad

  • 0 in reply to Kameshwar Prasad
    TI__Mastermind 19815 points

    Hi,

    You may want to make decision which DC method you want to test and set the registers accordingly -

    Bit 4 VLEAD_OFF_EN: Lead-off detection mode -

    0 = Current source mode lead-off (default)

    1 = Pull-up/pull-down resistor mode lead-off

    Then, the

    "

    b). Lead OFF comparator Threshold - Positive Side - 70% and Negative side - 30%.

    c). Lead OFF current magnitude - 16nA.

    "

    are something that need to be tested and figured out through experiments&tests.

    ----------------------------------------------

    As described in page 57-

    "The reference level of the comparator is set to determine the acceptable RLD impedance threshold."

    "The comparator thresholds are set by the same LOFF[7:5] bits used to set the thresholds for other negative inputs."

    So, you may want to play/adjust LOFF: Lead-Off Control Register's Bits[7:5] COMP_TH[2:0]: Lead-off comparator threshold.

    It could be possible that you need to set different threshold values for the RLD lead off detection.

    ------------------------

    regarding to schematic, you may first use the schematic in page 53 here https://www.ti.com/lit/ug/sbau171d/sbau171d.pdf?ts=1681316296221&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FADS1198ECGFE-PDK

    as a reference to see if there is any significant different issue.

    e.g.

    1. Why is there an R10 0 ohm short between RLDOUT and RLDIN?? Please pay attention to datasheet page 9 -
    "RLDIN 3A Analog input Right leg drive input to MUX. If unused, short to AVDD."  So, if you don't know why R10 0 ohm is there, please consider depopulating it first and redo tests.

    2. the R,C for RLD are different, but those are also something designers have option and may want to tune with respect to the product designs and usage.

    Thanks