A Python library for the Maxim MAX30100 pulse oximetry chip

This library provides a basic Python interface to the MAXIM MAX30100 heart rate and Sp02 sensor chip. Other libraries are available (e.g. Intel's UPM) but these are not easily compiled on a Raspberry Pi.

This library is a Python re-implementation of original C library by Connor Huffine/Kontakt, available here, with a slightly different API + additional features (buffering values, etc.).

Currently this library supports both IR led (pulse) and red led (SpO2) modes, with support (via gpiozero) for catching on-board interrupts and triggering real-time measurements. The examples below demonstrate a common setup. Calculations for converting measured values into actual number are not yet included.

Basic setup

You can create an interface to your device/chip by creating an instance of the MAX30100 class.

import max30100
mx30 = max30100.MAX30100()

You can pass a number of optional parameters to configure the initial setup, including:

• i2c a custom i2c object, if you already have a connection option to the bus
• mode to enable SpO2 readings by default
• sample_rate number of data samples to take per second
• pulse_width the duration of each sample
• led_current_red amount of current to supply to the red LED
• led_current_ir amount of current to supply to the infrared LED
• max_buffer_len the number of measurements to store locally

The values for sample rates, pulse widths and led currents are restricted. For the full list see the source code. If you provide an invalid value the correct values are displayed for convenience.

The precise meanings for each of these values is given in the MAX30100 datasheet.

Reading values

To read current sensor values from the MAX30100 chip you can call .read_sensor. This will retrieve the latest values from the buffer and store them locally. The latest values are available under .ir and .red for IR and Red measurements respectively. A local FIFO buffer is used to store previous measurements, up to max_buffer_len specified when setting up.

mx30.read_sensor()

# The latest values are now available via .ir and .red
mx30.ir, mx30.red

Take SpO2 (oxygen saturation) readings

To enable Sp02 reading, you can either set the mode directly, or use the convenience method:

mx30.set_mode(max30100.MODE_SPO2)
# or...
ms30.enable_spo2()

If you perform another sensor read, you will now see a value for the .red parameter (which is neccessary to read oxygen saturation).

mx30.read_sensor()
mx30.ir, mx30.red

The previous measurements are available in .buffer_ir and .buffer_red.

Automating measurements

The MX30100 chip provides an interrupt mechanism which can be used to trigger readings once values are available. Using gpiozero we can connect this interrupt trigger to the MAX30100.read_sensor method, resulting in real-time measurement output in our FIFO buffer. Connect the INT pin of the MAX301000 to a suitable pin on your controller. For example —

mx30.set_interrupt(max30100.INTERRUPT_FIFO)  # Set up a trigger to fire when the FIFO buffer (on the MAX30100) fills up.
                                             # You could also use INTERRUPT_HR to get a trigger on every measurement.

from gpiozero import Button  # A button is a good approximation for what we need, a digital active-low trigger
interrupt = Button(16)  # Pick a pin
interrupt.when_activated = mx30.read_sensor  # Connect the interrupt

You can now see the values in the buffers, e.g.

mx30.buffer_red

Or if that's too much, tail the most recent values, e.g.

while True:
     print(mx30.buffer_red[-10:])