Using the ADS131M0x Analog to Digital Converter

This tutorial demonstrates how to use the ADS131M0x analog to digital converter with the Open Source Leg platform. This example shows how to:

• Initialize and configure an ADS131M0x ADC
• Read voltage data

Hardware Setup

1. Connect the ADS131M0x ADC to your Raspberry Pi's SPI pins
2. Make sure the ADC is powered on and the SPI pins are connected correctly

Code Structure

The tutorial script is organized as follows:

1. Initialization

from opensourceleg.logging.logger import Logger
from opensourceleg.sensors.adc import ADS131M0x
from opensourceleg.utilities import SoftRealtimeLoop

FREQUENCY = 500
DT = 1 / FREQUENCY

if __name__ == "__main__":
    adc_logger = Logger(
        log_path="./logs",
        file_name="reading_adc_data",
    )
    clock = SoftRealtimeLoop(dt=DT)
    adc = ADS131M0x(
        tag="ADS131M0x",
        spi_bus=0,
        spi_cs=0,
        data_rate=FREQUENCY,
        clock_freq=8192000,
        num_channels=6,
        gains=[1] * 6,
        voltage_reference=1.2,
        gain_error=[0] * 6,
        offline=False,
    )
    adc_logger.track_function(lambda: adc.data, "Ch Voltages")

This section:

1. Creates a data logger for recording measurements
2. Sets up a real-time loop for consistent timing
3. Initializes the ADS131M0x ADC with specified parameters
4. Gets the latest ADC data in millivolts

2. Main Loop

    with adc:
        adc.calibrate()
        for t in clock:
            adc.update()
            adc_logger.info(f"Time: {t}; Ch Voltages = {adc.data}")
            adc_logger.update()

The main loop:

1. Updates the ADC to get the latest reading
2. Logs the time and current voltage reading

ADC Parameters

When initializing the ADS131M0x ADC, several parameters can be configured:

    adc = ADS131M0x(
        tag="ADS131M0x",
        spi_bus=0,
        spi_cs=0,
        data_rate=FREQUENCY,
        clock_freq=8192000,
        num_channels=6,
        gains=[1] * 6,
        voltage_reference=1.2,
        gain_error=[0] * 6,
        offline=False,

Parameter Details

1. tag (str):

   • Unique identifier for the ADC instance
   • Useful when using multiple ADCs
   • Default is "ADS131M0x"

2. spi_bus (int):

   • SPI bus number
   • Default bus on Raspberry Pi is typically 0

3. spi_cs (int):

   • SPI chip select line
   • Default is 0

4. data_rate (int):

   • Sampling rate in Hz
   • Default is 500 Hz

5. clock_freq (int):

   • SPI clock frequency in Hz
   • Default is 8192000 Hz.

6. num_channels (int):

   • Number of ADC channels
   • Default is 6

7. gains (List[int]):

   • Programmable gain values for each channel
   • Default is [1] * num_channels.

8. voltage_reference (float):

   • ADC reference voltage in volts
   • Default reference for ADS131M0x ADC is 1.2 V and should not be changed if using this ADC

9. gain_error (List[int]):

   • Gain error correction values for each channel
   • Default is None.

10. offline (bool):

    • Enables and disables offline mode for ADS131M0x ADC
    • If True, the ADC operates in offline mode, meaning that the ADC hardware does not have to be connected in order for your script to run
    • Default is False

Available Properties

The ADS131M0x ADC provides the following properties:

1. is_streaming

   • Checks if ADC is streaming data
   • Returns True if streaming, False otherwise

2. gain:

   • Gets the programmable gain values for each channel
   • Returns array of gain values (np.ndarray)

3. data

   • Gets the latest ADC data in millivolts
   • Returns array of voltage readings for each channel (np.ndarray)

4. data_counts

   • Gets the latest ADC data in raw counts
   • Returns array of raw ADC counts for each channel (np.ndarray)

5. num_channels

   • Get the number of ADC channels.
   • Returns # of channels (int)

Running the Example

1. Navigate to the tutorial directory:

   cd tutorials/sensors
   

2. Run the script:

   python reading_adc.py
   

3. Expected behavior:

   • ADC begins reading voltage values in mV continuously at sampling rate (default is 500 Hz)
   • Data is logged to ./logs/reading_adc_data.csv

Common Issues

If you have any questions or need further assistance, please post on the Open Source Leg community forum.