ADS1298: Read 2 Leads whit 3 electrodes

luis juarez

Part Number: ADS1298

Hello, im doing a mobile application that recieve 12 ECG derivations and graph the 12 derivations.

First, im triyng to read channel 2 and 3 form the ADS and display the data in a graphic, but i have signals that do not look like ECG. I have 2 questions.

1.- The channel 2 and channel 3, have LEAD I and LEAD II.

I am rigth?

2.- can you tell me if my configuration in the registers is the correct?

My configuration:

0x01,        0x86
0x02,        0x10
0x03,         0xdc
0x04,         0x1d
0x05,         0x81
0x06, 0x00
0x07,         0x00
0x08, 0x81
0x09,         0x81
0x0a,         0x81
0x0b,         0x81
0x0c,         0x81
0x0f,          0xff
0x10,         0x00

over 7 years ago

0 Alexander Smith over 7 years ago

TI__Guru 55662 points

Hello Luis,

Thanks for your post!

Since all of the input channels of the ADS1298 are the same, it is not important which lead is tied to which channel. However, If you are using the ADS1298R and using the respiration feature then Ch1 must be used for respiration.

However, now that I have reviewed your register settings I see that Ch1 & Ch3-8 are powered down and input shorted, while Ch2 & Ch3 are for normal electrode input. From the information you provided, this is correct.

Register 0x0f shows that lead off detection is enabled for all positive channels and 0x10 shows that lead off detection is disabled for all negative channels. I believe that this should be changed such that lead off detection is enabled on C2 & Ch3 for both positive and negative inputs. Please write 0x06 to both the 0x0f and 0x10 register.

0 luis juarez over 7 years ago in reply to Alexander Smith

Prodigy 140 points

Hello Alexander, i tried the configuration that you give me, but the signal still wrong.

there is a picture of the graphic.

0 Alexander Smith over 7 years ago in reply to luis juarez

TI__Guru 55662 points

Hello Luis,

What are you using to generate the input signal?

Can you post your schematic?

0 luis juarez over 7 years ago in reply to Alexander Smith

Prodigy 140 points

i dont know what you mean with what i using to generate the input signal.

i used this schematic

0 Alexander Smith over 7 years ago in reply to luis juarez

TI__Guru 55662 points

Hi Luis,

Thank you for providing the schematic. I will review this and get back to you soon.

What type of signal are you applying to the inputs of the device? Are you using an ECG signal generator?

0 luis juarez over 7 years ago in reply to Alexander Smith

Prodigy 140 points

thank you Alexander, i use electrodes conected to a person, 2 electrodes in the arms one in the left leg.

0 Alexander Smith over 7 years ago in reply to luis juarez

TI__Guru 55662 points

Happy to help Luis!

I see. We do not recommend testing/debugging using a real patient as it can be difficult to narrow down where the issue lies. However it it important for real time measurement that the electrode has a solid connection and that the movement of the patient is limited.

Are you using the RLD? I see from your register settings that the 0x03 register has a value of 0xdc which indicates that RLD_MEAS is 1. "RLD_IN signal is routed to the channel that has the MUX_Setting 010 (VREF)". However looking at your channel settings (0x05-0x0C), none of them are routed to RLD. Setting Ch2 (0x06) and Ch3 (0x07) to 0x02 may improve your RLD.

0 luis juarez over 7 years ago in reply to Alexander Smith

Prodigy 140 points

Hi Alexander, im not using RLD, i made a mistake in the register 0x03 i have modified the value to 0xc1. Should i use RLD?

0 Alexander Smith over 7 years ago in reply to luis juarez

TI__Guru 55662 points

Hi Luis,

I understand. I recommend using the RLD in order to eliminate the common mode noise. The lights and mains noise can overpower the measured signal, using the RLD will greatly reduce this noise.

0 luis juarez over 7 years ago in reply to Alexander Smith

Prodigy 140 points

Hi again Alexander, to use RLD, i have to connect a fourth electrode?

another question, how to know wich channel is routed to RLD?, the schematic that i gave you, it was provided by a partner of my university, but i dont know what channel use in the RLD configuration, can you help me with this?

Regards

0 Alexander Smith over 7 years ago in reply to luis juarez

TI__Guru 55662 points

Hello Luis,

Yes, you need an additional electrode in order to connect the RLD to the patient.

RLD is typically an average of RA, LA, and LL.

The RLD section of the user guide may be helpful for you:
www.ti.com/.../sbau171d.pdf

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ADS1298: Read 2 Leads whit 3 electrodes