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Precision Data Converters
Precision Data Converters Forum
Respiration with the ADS1298R but without MMB0
My setup is as following:
I have connected the EVM via SPI to a custom board with an MSP430.
My goal is to transmit both, ecg and respiration signal, via bluetooth.
To achieve this, I'm reading out (single shot mode) 256 times per second the ecg and 16 times per second the respiration signal.
(because I can only transmit 16Bit at once, the last 8Bit are cut off)
While the ecg is perfectly fine, the respiration is a huge mess.
Is there any magic which has to be applied to the respiration signal?
Strangely, there is not much change in the value I get back on channel 1: only the lsb (and rarely the next bit changes) (still 16Bit)
With the MMB0 and the software it was shipped with, everything works fine, even when the register settings are the same.
Only difference: With the MMB0 I used continous mode, because in single shot mode, the program froze.
Why can't I just transmit the Channel 1 readout 16times/second, display it in Labview as beautiful curve and be happy?
The software is designed and configured for evaluation purposes only. When designing the software, it was configured so that single shot mode is not supported.
The software is designed in LabView and the source code is available if you wish to modify the code for your particular application/needs.
Precision Data Converters
If I remember correctly, the zip with the source code was password protected?
Could you mail me the password to email@example.com? What was the link to it again?
And: What can I have done, that I don't get valid values over SPI? If I don't make a mistake, even 16Bit should be enough resolution for the test signal, even without PGA.
The data is sent MSB first, so it does not hurt it, when I cut the last 8 Bits, does it?
As the ECG seems to work, it should not be a problem with my SPI or later bluetooth transmission.
My only change to the MMB0 is, that in my configuration AVDD is 3.0V und DVDD 3.1V, but this should not matter?
Register settings should be correct.
Now that I have the password: Is there a driver for this usbstyx thing for Windows 7 64Bit?
I have "made" myself a VISA driver with the corresponding NI toolkit, but this was not possible for the usbstyx driver.
We have been updating the software to be compatible with Win7 and finished beta test program last week. We hope to release the new software within the next couple of weeks.
Would it be possible to grant access to this beta version? At least of the drivers?
I should have finished my project in a couple of weeks, so this could impose some problems.
Our beta program is finished, so we are not distributing the code any more. We are working to improve the content, fix any reported issues, and update a couple items (driver stuff included). So therefore, we would ask that you wait until the final product is released to prevent any known issues from causing problems or having multiple variations of the code running around.
I discovered that my problems do not start until I activate the respiration DEmodulation circuitry (RESP register, bit 7)
Each of the other options let the ADC on channel 1 operate properly.
I suppose this is the wanted behaviour, because of the deactivated demodulation circuitry, but at least it shows that nothing else should be defective.
So I have some questions:
1) I assume that the respiration function should also work in single shot mode. Correct?
2) Do I have to read more than one respiration signal at once? At the moment I have a function which just reads 216bits via SPI and which is called 16 times per second.
3) Do I have to do something with the respiration signal besides just transmitting it. For example averaging it?
4)Does the respiration function need a longer span of time to work after the start than the rest?
For your previous question, the ADS1298R source should be the same as the ADS1298 source - minus a couple bits. I can certainly link you to the current source if you need it. The new software to be released soon will cover both ADS1298 and ADS1298R, so this will be just one source when released.
Regarding your questions -
So I think there are a few items that need clarification:The ADS1298 device is a delta-sigma ADC; it sounds like you are trying to run it more like a SAR converter to control the data rate. This doesn't necessarily work since every sample you take with single shot, you are resetting the internal digital filters of the device. The single shot mode was more intended on DC/general purpose ADC application rather than ECG applications.
The respiration function won't work in single shot mode due to the modulation requirements. See http://www.ti.com/lit/an/sbaa181/sbaa181.pdf for further details.
In terms of the transmitted data, one reason your respiration signal may be a mess is that you are throwing away the important bits. In discarding the lower 8 bits of the data, you are discarding most of the respiration signal - it is a very low magnitude signal. So you will need to figure out a way to transmit/save those bits for proper processing of the RESP signal.
Take a look at this short slide set as well.
Thank you for your answers.
So you would recommend to let the ADC run in continous mode. But only picking out one sample every 1/16 seconds should be fine?
Besides this I don't have to pay attention to other "traps"?
Sorry for my stupid questions, but I am still a beginner regarding this.
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