how many electrodes we can connect throw ads1298 directly and how ??

Hey Harsh,

The ADS1298 has 8 conversion channels, so you can have as many electrodes as you need to make 8 simultaneous measurements. For example, on the ADS1298 EVM, there are available connections for RA, LA, LL, RL, and V1-V6. In that setup, you would measure Lead I and Lead II and calculate Lead III from the first two. Then you would use the integrated WCT amplifier to connect the WCT output to the negative inputs to the channels connected to V1-V6. I'd advise you look at the user's guide for the EVM for a schematic.

Regards,
Brian PIsani