EMG application using ADS1298

FRANCOIS DE LA ROCHE SAINT ANDRE

Other Parts Discussed in Thread: ADS1298

Hi,

I read all the previous post related to this subject but there are still some points that are not clear to me.

I would like to use the ADS1298 for measuring and recording EMG signals, beginning with the available ADS1298ECG demonstration board.

From what I understood, EMG signals have the biggest amplitude among the different body signals (Signals) : EMG>ECG>EEG.

In the ADS1298ECG manual, it says that we can directly hook-up ECG signals to ADC inputs without any preamplifier stage for a proper use.

From this app note I understand that only EEG signals will require a preamplification as they are weak and using directly AD converter will bring a lot of noise.

My conclusion is that I would not need any preamplification for EMG signals as their amplitude is higher than ECG, could someone correct me?

Is the PGA stage sufficient for amplifying EMG signals so that the dynamic range could fit with the ADC input?

Could someone advice me on the procedure and stages required to use the ADS1298ECG in the best way possible for EMG measurement?

About the demonstration kit, I understood that I could use it with any microcontroller boards besides the MMB0 as it use a SPI interface.

My question are:

- Could I develop my own application to get the raw data from the ADC channels? Could I use a software like Matlab to plot the data?

- Could I program DSP present on the MMB0 like a microcontroller (C language)? Could I use CCS or IAR?

- If not, could someone advise me on other boards that could be easy to use (microcontroller) with the ADS1298ECG board? Is there a MSP430 development board ready for that? In this case could where could I get the ADS1298ECG board only?

Thanks very much in advance, hope you can provide me these information.

Regards.

over 13 years ago

0 Tom Hendrick over 13 years ago

TI__Guru**** 181001 points

Hi Francois,

Welcome to our forum! The ADS1298 should be able to collect EMG signals directly without a pre-amp stage. Adam Freed was doing something along these lines with a processor other than the MMB0, so he may have some information to share with you, take a look at this post:

http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/p/104415/363882.aspx#363882

The MMB0 could conceivably be used as a development board, but it is not really supported in that capacity. You would need a JTAG programmer and would have to have a full version of CCS to do so. The MAVRK team is building up an ADS1298-MVK platform that will use an MSP430 as its host controller, so that is another potential avenue for you.

0 FRANCOIS DE LA ROCHE SAINT ANDRE over 13 years ago in reply to Tom Hendrick

Prodigy 155 points

Hi Tom,

Thank you for your quick reply. I checked out the link you posted, seems like I have a good staring point (I finally bought the demo kit).

I'll contact this person in case I get into troubles.

I see, this ADS198-MVK is pretty interesting but I may not need the entire system.

Thanks,

Francois

0 FRANCOIS DE LA ROCHE SAINT ANDRE over 13 years ago in reply to FRANCOIS DE LA ROCHE SAINT ANDRE

Prodigy 155 points

Another question concerning the user's manual.

So I got the board today, and I was having a hard time understanding which jumpers is what, I have some notation on my actual board (Rev C) that differ from your gerber files and schematics (Rev A) in the manual.

I fortunately found this updated layout: http://e2e.ti.com/support/data_converters/precision_data_converters/w/design_notes/1535.aspx

It says: "Page 17, Table 4 lists the default jumper settings." As I don't see it in the manual, I was wondering if is there a new version (mine is a revision from January 2011) and if is there any way I can get it?

If there is no updated manual, could I get the updated schematics and printed gerber files (PDF) from the ADS1298ECG board ?

Thank you very much.

Francois

0 Ava Ghafari over 10 years ago in reply to Tom Hendrick

Prodigy 80 points

Hi,
I wanted to add another question about using ADS1298 for measuring and recording EMG signals..
What external filters do I need for input signals?I mean what is the frequency range of ADS1298 inputs?and is it okey to put 2nd order Sallen key filter for the input signal?

0 Brian Pisani over 10 years ago in reply to Ava Ghafari

TI__Mastermind 38745 points

Hey Ava,

Active filtering is typically not necessary for delta-sigma ADCs. The device samples much faster than the output data rate and averages which will eliminate a lot of out-of-band noise. That being said, all digital filters respond periodically at integer multiples of the sampling frequency. In the case of the ADS1298, that frequency is the modulator frequency which is either 512 kHz or 256 kHz, depending on whether the device is configured in High Resolution or Low Power mode, respectively. The filter you need at the input only needs to have a sufficiently attenuating response at either of those frequencies rather than the requirement be immediately after the data rate divided by 2. In addition, the PGA on this device has limited bandwidth which will also serve as a convenient anti-aliasing stage (see table 16 in the data sheet). In most cases, sufficient anti-aliasing external to the device may be achieved with either a single or double pole passive low-pass filter.

As a disclaimer, be careful about component mismatch leading to common-mode rejection issues on your board. One thing that makes me wary about the Sallen-Key idea is that component mismatch will lead to poor common-mode rejection performance at lower frequencies that you might want to reject (i.e. the utility frequency). With a simple RC filter, you can push the cutoff frequency well past your signal bandwidth as a means to downplay the effect of component mismatch and rely heavily on the digital filter for band-limiting and the PGA (which has excellent CMR) for anti-aliasing.

Regards,
Brian Pisani

0 Ava Ghafari over 10 years ago in reply to Brian Pisani

Prodigy 80 points

Hi Brian,

your answer was really helpful,

I will do what you said!

thanks in advance

Ava

0 Ava Ghafari over 10 years ago in reply to Brian Pisani

Prodigy 80 points

Hi Brian,
thanks so much about the answer, but I have too many questions to ask...
1.for EMG use, do the Electrods need Buffers(to amplify the current)?
2.if we dont use batteries as the voltage source , what isolators do you recommend?

regards
Ava

0 Brian Pisani over 10 years ago in reply to Ava Ghafari

TI__Mastermind 38745 points

Hey Ava,

1. The inputs to the ADS1298 are high impedance and will thus draw very little current. You may want to amplify the voltage at the inputs. There is a highly configurable PGA integrated on the chip for that purpose.
2. We have no recommended isolators for the ADS1298. One thing to keep in mind when isolating the digital communication lines is that SPI is a full-duplex communication protocol and thus there are strict setup and hold time requirements that must be met. Ensure that whatever isolator you decide on does not contain so much propagation delay as to violate those timing requirements on page 15 of the datasheet.

Regards,
Brian Pisani

0 Sidharth Pancholi over 9 years ago in reply to Brian Pisani

Prodigy 25 points

1.sir i want to ask weather simple RC band pass filter at the input channel we need of desire range? like emg 10 to 500hz band pass filter we need at the input stage ?
2.should we add ther notch filter also for each input channel?

0 Brian Pisani over 9 years ago in reply to Sidharth Pancholi

TI__Mastermind 38745 points

Hey Sidharth,

1. Refer to this post: e2e.ti.com/.../479424
2. You may want to for 50/60 Hz power supply interference, but this can most easily be done with a digital filter.

Regards,
Brian Pisani

0 Sidharth Pancholi over 9 years ago in reply to Brian Pisani

Prodigy 25 points

sir,
Thanks for the reply
sir after getting signal in controller (spi protocol) ,in the processor how we can separate it again channel by channel , or what is the way to see data in real time .

0 Brian Pisani over 9 years ago in reply to Sidharth Pancholi

TI__Mastermind 38745 points

Hey Sidharth,

That will require some programming skill :-) . At the end of the day it will be a matter of doing a series of logic operations to separate the data into different locations of memory. There is no special way of doing it. As for seeing the data in real time, that is sort of up to you for your application.

Regards,
Brian Pisani

0 billlin over 8 years ago in reply to Brian Pisani

Prodigy 50 points

Hi ,

Excuse me I still don't understand for measuring and recording EMG signals.

So if i wanted to measuring EMG signals, can i just using the same setting for ECG?
Or i need to set new setting for EMG, like sampling rate?

i'm sorry for my poor english and stupid question.

Regards,
Bill Lin

0 Brian Pisani over 8 years ago in reply to billlin

TI__Mastermind 38745 points

Hello Bill,

See this post: e2e.ti.com/.../2209424

Brian

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EMG application using ADS1298