SmartMedics

Clarification and conceptual design

We worked with the customer to prioritize product requirements. We did this by waying the design implications versus the business value. For example features like continuously informing the user through LED’s about the device status have an impact on battery consumption, requiring a larger battery.

The main use case asks for the device to be as small and light as possible which requires a small battery. We scoped the device to an MVP and a final product, this allowed us to deliver the product much faster and meet the business requirements of the customer. 

System Design

After clarifying and removing ambiguity from the requirements we selected a HW platform to support the requirements and created a system architecture. One of the challenges was to be able to support the high data rate to transport and process all the sensor data while using a low power wireless connection.

We chose Bluetooth Low Energy for transmitting the data as it enabled us to maximize the data throughput while being power efficient. We leveraged the power optimized features of the BLE component and applied it to function as the main controller of the device. The design had to be made really power efficient to support a run time of at least 24 hours, allowing a full day recording and processing of ECG data.

Implementation

For this design it was a challenge to make the device withstand high energy defibrillation surges, which normally use big and chunky components and a lot of space on the PCB. We were able to make this very compact with the right components and using PCB technology to the max.

As in most projects, the cooperation between HW designer and mechanical designer must be tight to be able to get the best solutions. The design needed an easy way to attach and detach the device from the patch, without applying excessive force (to the patient) , while keeping a small formfactor. A special locking mechanism with pogo pins for the electrical connection did the trick.

Certification of the product played an important role in this development and dictated our software development approach. The timeslot for CE and medical certification (MDD) was already booked, therefore the focus was on hardware certification. Minimalistic software was written to perform the tests and later the mobile application was created, which utilized the created and certified software.

The design is based on the Nordic nRF52 series Micro Controllers with BLE, combined with an ST microcontroller to readout and process the ECG Frontend data. The acquired data is transmitted through bluetooth as quickly as possible and to facilitate other use cases on board FLASH is available to store data locally. To minimize battery use/size, the design includes several power management options.