Portable Medical Instrument Design
Portable Medical Instruments device design: blood glucose meter design, blood gas meter, digital pulse/heart rate monitor and digital thermometer design.
Go passive. Go battery free! With the Passive Low Frequency Interface Device (PaLFI) TMS37157, power your microcontroller, sensor, and sensor interface at short range by the PaLFI interface without a battery.
Whether developing a glucose meter, blood pressure meter, blood gas meter, digital thermometer, or a heart rate monitor there are system level blocks that are common to each: Power/Battery Management, Control and Data processing, Amplification and A/D Conversion, a display, and the sensor element itself. These are microcontroller controlled handheld devices that operate on battery and take measurements using various bio-sensors, with the topology of these blocks differing with the sensing, processing and information display demands of the meter type and feature set.
Power consumption is key, driven by the need for extended battery life, and high precision with a fast response time. Requirements such as wireless or wired connectivity, historical data profiling and audio or voice feedback drives the need for microcontrollers with adequate memory. Texas Instruments' portfolio of Microcontrollers, Instrumentation and Buffer Amplifiers, Wireless and Wired interface devices, Power and Battery Management, and Audio Amplifiers provides the ideal tool box for portable medical applications.
The common core subsystems are:
- Analog Front-End/Sensor Interface - Bio-sensor signals in portable meters are slow moving and very low in amplitude. Front-end amplification may be required prior to A/D conversion. Front-end excitation, if required, can be accomplished with a discrete or integrated DAC within the microcontroller.
- Microcontroller - The Microcontroller executes the signal measuring processes and controls interface with memory and peripheral devices. As power consumption is critical, the broad product portfolio of the Ultra low power MSP430 family makes it an ideal processor choice. Their high level of integration simplifies the design and reduces system cost as buffer amplifiers, data conversion, LCD controllers, and user/keypad interface are provided.
- Connectivity - Power consumption, data rate and range are the three key considerations when selecting a wireless interface. The Zigbee protocol provides worldwide coverage, a moderate data rate and duty cycle, and supports a mesh network allowing multiple sensors in the same system with a wide range. Bluetooth and Bluetooth Low Energy® protocols provide for limited range but higher data rate.
Passive Low Frequency Interface products (PaLFI) are not only capable of providing near field wireless connectivity, but depending on your system power consumption, PaLFI is capable of powering your complete system.
- Power Management and Conversion - Making power management decisions early in the design cycle will help define system-level tradeoffs necessary to meet run-time targets. Smaller portable medical products may use disposable batteries, whereas larger portable systems might leverage rechargeable battery chemistries. Features such as dynamic power path management (DPPM) permit the system to draw power independently of the battery charging path. This allows a device with completely discharged batteries to be used as soon as it is plugged in, rather than waiting for the batteries to recharge. Also look for features such as Impedance tracking or battery authentication when safety and system reliability is critical.
- Audio Amplifier - The Audio Amplifier amplifies the audio signal coming either from a PWM circuit or a DAC which can be used to notify users when measuring results are available for example. The DAC is capable to output voice instructions from speech-synthesizer software.