STM32U5 + ADS1293: Clean ECG from Lead I, but Noisy/Incorrect Data from Lead II

 Trying to Interface ADS1293 with STM32U5 for 3-Lead ECG – Need Help with Lead II Data

Hi STM32 Community :waving_hand:,

We’re trying to build a 3-lead ECG signal acquisition setup using the ADS1293 analog front-end connected via SPI to an STM32U5G9ZJT6Q microcontroller. The goal is to capture and plot Lead I, Lead II, and derive Lead III using TouchGFX.

 What’s Going Well:

• We are able to receive and plot clean ECG data for Lead I (RA - LA) using CH1 of the ADS1293.

• SPI communication is stable, and the plotting is handled through TouchGFX without lag.

• Sampling is working at 500–1000 Hz using a DRDY-based interrupt routine.

What We’re Struggling With:

• When we try to configure CH2 for Lead II (RA - LL), the data appears noisy, flat, or unstable.

• We’re using the same initialization and acquisition process for CH2 as we did for CH1, but the result is not usable.

• For Lead III, we are trying to derive it in software using:

  Lead III=Lead II−Lead I\text{Lead III} = \text{Lead II} - \text{Lead I}Lead III=Lead II−Lead I

  But since Lead II is not clean, Lead III is also affected.

 What We Have Tried:

• Verified hardware connections and electrode placements – all seem correct.

• Swapped electrodes to check if the issue is with wiring – no improvement.

• Checked lead-off detection and ADC status flags – everything seems normal.

• Confirmed that CH2 is enabled and configured similarly to CH1.

• SPI read timing and DRDY sync appear to be correct.

 Our Current Register Setup:

 Reference:

We’re referring to the ADS1293 datasheet (TI document SLAS969), and focusing particularly on the channel configuration sections starting from page 43:

If anyone wants to verify the register details, please refer to those pages.

 What We’re Looking For:

1. Has anyone successfully acquired clean Lead II ECG data using ADS1293?

2. Are there any specific register settings or hardware considerations for CH2 (IN2–IN3) that we might be missing?

3. Would it be better to acquire only Lead I and Lead II, then derive Lead III entirely in software?

4. Is there any known issue or errata with CH2 channel configuration on ADS1293?

 System Summary:

• MCU: STM32U5G9ZJT6Q

• AFE: ADS1293 (SPI interface)

• Display: 5” TFT LCD via TouchGFX

• Electrodes: 3-lead (RA, LA, LL)

• Sampling: 500–1000 Hz, DRDY interrupt based

We would really appreciate any guidance, working examples, or known-good register maps for this use case. Thank you in advance!

—
Ganesh
Embedded Software Engineer