New 1292 Design software questions

Dale Zellers

Other Parts Discussed in Thread: INA333, ADS1292, ADS1298R, ADS1292R, ADS1293

We are developing a multi-function monitor which will include an ECG. The first requirement was single channel and I originally designed a traditional analog front end with buffers, an INA333 Instrumentation amp, some active filtering, and an ADC. Now our customer wants 2 channels, and oh can we make it cheaper and with less board space, so we are looking at the ADS1292 as a solution. As some background, we have a standard PC104 SBC with touch/LCD as the user interface, with I2C as our means for running all of our dedicated hardware. Our first decision is whether to just control the 1292 through a I2C to SPI bridge from our SBC, or to use one of your MSP430 family processors as is done on your ADS1x9xECG-FE board. Related to that are the following questions (from my software counterpart):

1) Is any of the software from the demo board available as a starting point for us to use, paricularly the filtering (such as 60 Hz notch) routines?

2) Since we will be using the I2C function, and since the I2C port in the MSP430 family is more general purpose than in a simple I2C dedicated device, am I safe in assuming that, particularly with operations that need to return a responce, such as data sampling and lead off monitoring, we would need to send a command for which we want to do, then wait for the MPU to load the relevant responce into a read buffer (with the "how do we know that it is done with that task" question) and then do a read of the results?

3) How hard is it to use the lead off function to do a rough lead resistance measurement?

Thank you

Dale Zellers

over 13 years ago

0 Greg Hupp over 13 years ago

TI__Mastermind 23235 points

Mr Zellers -

For the software aspect of your question, please request the information per sticky post at the top of the forum

0 Dale Zellers over 13 years ago in reply to Greg Hupp

Prodigy 30 points

Thank you Greg. This is just what we were looking for for item 1. My software counterpart has downloaded it.

Dale Zellers

0 Tony Calabria over 13 years ago

TI__Mastermind 43915 points

Hi Dale,

Looks like Greg took care of the question 1 you had.

2. I am a little confused on how you plan on configuring your setup and what you are using for your I2C to SPI conversion. The ADS1x9x requires SPI for communication in which you would want descent speed on your SCLK as ECG measurements rely on many conversions sequentially. You need to read them back as /DRDY indicates new data to successfully digitize the input signal. The data converter is free running and does not use a convert start signal to trigger when to begin conversions. Using the SPI from a MSP430 would be your best bet to get the data back. I am not sure where the I2C interface you are referencing is coming into play and why you need it. Also, generally the I2C interface is slower, so I am concerned that you can get the data back before new data is ready.

3. This is a question that has came up a few times now. I talk about it a little in the lead off application note that we recently released a few months ago here from a purely resistance stance

http://www.ti.com/lit/an/sbaa196/sbaa196.pdf

Issue lies in that every electrode has both a changing resistive and capacitive element. As the connection between the electrode and skin changes, both this capacitive and resistor element will change. From a purely resistive stance, you can send out an excitation signal and monitor the amplitude coming from that frequency. When factoring in the capacitive characteristics, you will need to sweep the frequency of the excitation signal to get an idea how the capacitance is changing. Some customers are using the respiration modulation/demodulation in the ADS1298R/ADS1292R for impedance tracking aside from respiration. I have not tried that but it should work in theory as long as the impedance you are trying to measure is low.

Regards,

Tony Calabria

0 Dale Zellers over 13 years ago in reply to Tony Calabria

Prodigy 30 points

Tony

Thank you for following up on these other issues.

We are exploring 2 possibilities, one (preferred) with a MSP430 to do the primary data collection and the filtering, and the other, should we have issues with getting all necessary software for the MSP430 happy within our schedule. In either case, I2C is how we get from our hardware to the PC104 SBC which is our user interface. We need around 200 samples per second to use the resolution of our display, so we would probably set the ADS1292 for its 250S/S rate if not using the MSP430. Our I2C clock is nominally 330KHz, which is about 33Kbytes/second, which even with a modest overhead should be enough. In the non-MSP340 case we are using a NXP SC18IS601 I2C to SPI bridge IC. If we use the MSP430, we would have one of its serial channels as SPI to talk to the ADS1292, and a second serial channel set as I2C slave to communicate with our SBC, both transfering the ECG data, and also commands for gain as channel setting, and for occasional lead resistance measurements, assuming we get there. I have just downloaded sbaa196 and will read it shortly. Our plan there is just to see if we have a reasonable connection. Back in the '70s when I first worked with ECGs, it was the practice to clean and lightly abraid the skin to ensure a good connection (under 10K DC). These days they count on the monitor input impedance to be high enough that they can just slap the pads on and go. My initial analog design used values that, shall we say, were not happy with a megohm connection to the patient. We have adjusted values and are now Ok there, but this is another reason to look into the ADS1292.

Does this clarify your confusion, and do you have any other thoughts or concerns?

Dale Zellers

0 Igor Korsakov over 12 years ago in reply to Dale Zellers

Prodigy 30 points

What is the password for ADS1x9x_ECG_RECORDER_USB_DLL ?

This zip files in the same directory

Thanks

Igor

0 Greg Hupp over 12 years ago in reply to Igor Korsakov

TI__Mastermind 23235 points

May we use the email address in your profile to provide the requested information? If this is not good, please provide an email address in this post or submit a request as detailed in the follow post: http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/254854.aspx