Controllers for Medical Wearable Sensors and Devices
Pulse
Octopart Staff
Aug 8, 2019

Industry Insiders 2 Wide

The future of sensors and sensor networks, and their applications in consumer electronics, medicine, and electronic equipment in industry, has become an important topical issue. The increased demand for wearable sensors that can be formed into sensor networks allows information to be quickly gathered over a large scale.

Sensors are basically devices which are used to generate an electrical signal in response to some physical change in the surrounding environment. A sensor converts physical quantities such as temperature, blood pressure, humidity, speed, etc. into an electrical signal that can be measured and quantified, which can then be used to calculate the magnitude of the physical disturbance that generated the signal.

Similarly, sensors for wearable devices can streamline a number of important activities, such as medical diagnoses. Greater productivity and safety demands have made sensors useful in more consumer electronics, personal items like clothing, and industrial PPE. Biomedical sensors are useful beyond medical diagnoses or monitoring; they have become applicable in agriculture, personal fitness, manufacturing, and any other area where someone may be working in a dangerous environment.

What is a Sensor Network?

A sensor network consists of a group of small, typically battery-powered devices with wireless connectivity that monitors, measures, and records changes in a number of physical phenomena. A sensor network can be used for environmental/geological sensing, health care monitoring, data logging, threat detection, and monitoring industrial equipment.

Individual wearable sensors and sensor networks can connect to the Internet, an enterprise WAN or LAN, or a specialized industrial network so that collected data can be transmitted to back-end systems for analysis. These devices must be designed with a specific topology (typically mesh or star topology), although this does not inhibit the type of sensors that can be used in each node of the network.

In the medical arena, multiple sensors placed on the human body allow monitoring of multiple vital signs simultaneously in a star topology, and the data can be sent back to a base station wirelessly for collection and analysis. In manufacturing and other dangerous environments, biomedical monitors and environmental sensors on workers can be connected in a star or mesh topology, which helps ensure worker safety while extending the usable range of the network over a larger area.

There are several types of sensors and controllers available for use in new products. No matter which type of sensor you use for your next product, or how the device connects to other sensor nodes, you’ll need to select the right controller and signal processing components for your product.

Signal Processing for Medical Wearable Sensors

The success of medical wearable devices mainly relies upon the integration of sensors with processing algorithms into a wearable form factor that allows medical professionals to focus on monitoring persistent diseases and improving outcomes for patients. Presently, these devices can provide continuous data acquisition of multiple vital signs. As research and development of wearable devices continues to progress, we can only imagine the advancements that are yet to be experienced in the realm of digital health.

Analog Devices, AD8233ACBZ-R7CT-ND

Wearable electrodes are usually placed against the skin in order to accurately measure electric pulses from the heart. Great improvements have been recorded in wearable medical clothing integration, but the integration is well secured to the extent that clothing can be washed without sensor removal. As an example, wearable electrodes are used to provide medical practitioners with a constant EEG, EKG, or even an EMG over an extended period of time.

The AD8233ACBZ-R7CT-ND biopotential signal processing block from Analog Devices provides precise filtering of biopotential measurements in a small form factor. This IC mounts to a 20-ball BGA with a WLCSP package, so it is still small enough that it can be packaged in a wearable device that interfaces with two or three wearable electrodes. It has excellent 80 dB common-mode noise rejection with high signal gain.

The AD8233 includes a fast restore function that reduces the duration of the otherwise long settling tails of the high-pass filters. After an abrupt signal change that rails the amplifier (such as a leads off condition), the AD8233 automatically adjusts to a higher filter cutoff. This feature allows the AD8233 to recover quickly, and therefore, to take valid measurements soon after connecting the electrodes to the subject.

AD8233ACBZ-R7CT-ND controller for wearable sensors from Analog DevicesAD8233ACBZ-R7CT-ND controller footprint and block diagram from the AD8233 datasheet

Maxim Integrated, MAX86150

Biochemical and biopotential sensors tend to be the most prevalent sensor type in medical wearables. A chemical sensing wearable device could be used as a diagnostic tool for chemical imbalances, ingestion or absorption of toxic substances, sickness like multiple chemical sensitivity (MCS), and other chemical-related ailments.

The MAX86150 sensor array provides integrated photoplethysmogram and electrocardiogram measurements for mobile health monitoring in a wearable device. This low power module (1.8 V supply voltage) is ideal for wearable applications. It also supports bidirectional communication with other devices via I2C, making it ideal for use in wireless wearable medical devices. This device nicely integrates data processing and standard biomedical sensors into a single package. It evens includes a proximity function:

The MAX86150 includes a proximity function to save power and reduce visible light emission when the user’s finger is not on the sensor...When the SpO2 or HR function is initiated, the IR LED is turned on in proximity mode with a drive current set by the PILOT_PA register.

Simplified block diagram for the MAX86150Block diagram for a typical wearable biomedical device from the MAX86150 datasheet

Controllers for Wearable Sensors and Sensor Networks

Wearable devices and nodes in sensor networks are essentially small embedded devices. After an analog signal is acquired and processed, it must be converted into digital data that it can be transmitted over a wireless network or easily interface with other components in a wearable device. This is typically done with a microcontroller, although ASICs can be used if desired.

A key factor to consider while choosing a controller for a wearable device is power consumption. Minimizing power consumption is essential as wearables and nodes in a sensor network are typically battery powered. Any microcontroller used in a wearable sensor should be power efficient. Another factor to consider is the life of the battery used in the device. The functionality of the input and output components should also be considered. Using a microcontroller that can enter sleep mode in an automated or semi-automated manner is a great choice for devices with wearable sensors or in wireless sensor network nodes.

Microchip, ATSAME53J19A-AU

The ATSAME53J19A-AU MCU from Microchip delivers low power consumption when compared to other MCUa in its class. This high-end power-efficient controller ideal is ideal for use in battery-operated wearable devices. It has a Sleep/Walking feature that enables peripherals to asynchronously wake-up from sleep in ULP1 mode. Note that this functionality is not limited to medical wearable sensors: it could also be used for data processing in networks of environmental sensors.

Photograph of the Microchip ATSAME53J19A ICMicrochip ATSAME53J19A microcontroller

Microchip, AR1010 MCU

In most wearable devices, the display screen is the primary input and output element. Other devices have other ways to provide information to the consumer through a user interface, such as touch panels, buttons, and sometimes motion sensing. The display screen still remains one of the most effective means of communicating with the user. This is where using a microcontroller with the right firmware can save a designer a significant amount of time when creating a new product.

Microchip mTouch® AR1000 Series Resistive Touch Screen Controller is an all-in-one, easy to integrate, budget-friendly and universal touch screen controller chip. The firmware in the AR1010 controller includes touch screen decoding algorithms for processing touch data. This particular feature eliminates the need to manually implement a decoding algorithm and gives a designer more flexibility. It also provides excellent filtering capabilities when compared to other low-cost devices. This makes the AR1000 deliver authenticated, reliable, and calibrated touch coordinates.

Photograph of the Microchip AR1010 ICMicrochip AR1010 microcontroller

Using the right combination of embedded processing can accurate sensors can ensure accurate data acquisition while supporting graphics display on a touch screen. The devices we’ve presented here are only a portion of the sensing options available for use in wearable devices and sensor networks. In the realm of wearable sensors, many ICs that can interface with a touch screen and multiple sensors are packaged on evaluation boards, giving you some level of freedom to prototype your next wearable product.

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