Hi IT experts,
In our wearable project, we adopt TI's ADS1293 frontend for ECG capturing. Three Electrodes are connected for one channel capturing.
below snippet is the configuration of the device.
void ads1293_config()
{
// stop conversion
ads1293_write_register(0x00, 0);
// Connect channel 1’s INP to IN2 and INN to IN1.
ads1293_write_register(0x01, 0x11);
// Connect channel 2’s INP to IN3 and INN to IN1
// spi_writereg(TI_ADS1293_FLEX_CH2_CN_REG, 0x19);
// Enable the common-mode detector on input pins IN1, IN2.
ads1293_write_register(0x0A, 0x03);
// Connect the output of the RLD amplifier internally to pin IN4.
ads1293_write_register(0x0C, 0x04);
// Use external crystal and feed the internal oscillator's output to the
// digital.
ads1293_write_register(0x12, 0x04);
// Shuts down unused channel 2&3’s signal path.
ads1293_write_register(0x14, 0x036);
// 100 Hz ODR
// Configures the R3 decimation rate as 64 for channel 1, 2, 3.
ads1293_write_register(0x22, 0x40);
ads1293_write_register(0x23, 0x40);
ads1293_write_register(0x24, 0x40);
// Configures the DRDYB source to channel 1 ECG (or fastest channel)
ads1293_write_register(0x27, 0x08);
// Enables channel 1 ECG for loop read-back mode
ads1293_write_register(0x2F, 0x10);
// high resolution mode for ch1
// ads1293_write_register(0x13, 0x01);
// clear bit 3 (SHDN_LOD) of register 0x06 to enable
// LOD clear bit 2 (SELAC_LOD) for DC LOD
ads1293_write_register(0x06, 0x00);
// enable the lead-off-detection for input IN1, IN2 dn IN4
ads1293_write_register(0x07, 0x0b);
// The lead-off detect current is programmable in a range of 2.04μA
// with steps of 8nA
ads1293_write_register(0x08, 0x0f);
// start conversion
ads1293_write_register(0x00, 1);
}
The device works and ECG signal can be captured. but we are facing a critical issue. the signal captured usually has severe baseline wandering in a frequency inside ECG frequency spectrum. for example.
This makes post processing like filtering smoothing difficult. We are wondering whether these signal waveforms are as expected or not. Could you please give us any instructions to improve the signal quality?
BTW, we bought an ads1293evm board for evaluation, we didn't really manage to capture any valid signal from the EVM board. Therefore we don't have anything to refer to except the datasheet.
Any of your help will be appreciated.
