converting ADS1298 Data

Mehdi Bentayaa

Other Parts Discussed in Thread: ADS1298, ADS1299, ADS1278

Hi!!

I have some trouble converting data from ADS 1298.

I use ADS with PIC18F and I managed to get the SPI data from ECG simulator and send it to the PC via UART to USB connector.

I have trouble in converting 2's complement values that are cutted and there are spikes coming from a bad conversion (I think).

Can I have more information about Dout SPI data format and 2's complement conversions?

Thanks for answering.

Mehdi.

over 13 years ago

0 Tom Hendrick over 13 years ago

TI__Guru**** 180901 points

Hi Mehdi!

Are you just having trouble with the B2C to straight binary conversion or is there something about the data transmission from the ADS1298 that you need help with? We don't have any code specific to the PIC18, but we might be able to point you to a generic 'C' routine that will do the conversion for you.

0 Mehdi Bentayaa over 13 years ago in reply to Tom Hendrick

Prodigy 65 points

Hi Tom!!

Thanks for answering.

For my tests I send all data to Matlab and the conversion is done by a Matlab routine.

I guess the data I get from ADS is correct. Actually I think I have trouble only with B2C to straight binary conversions or sending data to Matlab.

I check with ADS1298 ECG-FE PDK and the signal shape I have with Matlab is roughly the same except the spikes and some saturation/inversions.

I would like some information about the SPI byte sequence on Dout and B2C to straight binary conversions (OK for generic 'C' routine).

Once the conversion is done in uC, the data sent does not need any other conversions, just be processed as 'normal' unsigned 24 bit signed integer?

Thanks a lot!

Mehdi

0 Mehdi Bentayaa over 13 years ago in reply to Mehdi Bentayaa

Prodigy 65 points

Just to correct my last sentence :

Once the conversion is done in uC, the data sent does not need any other conversions, just be processed as 'normal' 24 bit signed integer?

Thanks.

Mehdi.

0 Tom Hendrick over 13 years ago in reply to Mehdi Bentayaa

TI__Guru**** 180901 points

Hi Medhi,

Here is the post I was thinking about WRT format conversion:

http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/102784.aspx

0 Mehdi Bentayaa over 13 years ago in reply to Tom Hendrick

Prodigy 65 points

Hi Tom!

Thanks for your reply.

I tried it and it seems to be ok.

Regards,

Mehdi.

0 Benjamin Madison over 9 years ago in reply to Mehdi Bentayaa

Prodigy 40 points

I know this post is a few years old, but given it provides some pretty solid conversion advice, I thought I'd answer the final question.....

All ADS family devices send ALL bytes back every time you grab data. If you have a ADS1299 (8 channels) but you're only running 1 channel, you still must account for:

3 byte header

24 bytes data (3 bytes * 8 channels) although the channels off will be all 0.

0 Ryan Andrews over 9 years ago in reply to Benjamin Madison

TI__Guru 66206 points

Hello Benjamin,

What you claimed does not hold true for ALL ADSxxxx devices. For example, our ADS1278 offers several different data output modes. One of which is called Time Domain Multiplexed (TDM) Dynamic Position, which removes any powered-down channels from the output data stream.

In contrast, the ADS1298/99 only offer a fixed-position data output mode. In this case, powered-down channels must still be accounted for just liked you described.

Thanks and regards,

Data converters

Data converters forum

converting ADS1298 Data