Design of low power medical data logger

Many medical applications require portable, self-powered devices that do not require an external power cord and data line. The most obvious example is a portable data logger that the patient carries with them to measure heart rate, body temperature, and other health indicators.

Of course, there are many complex applications that require a small battery device to achieve safety redundancy and equipment monitoring, even when powered by an external power source, such as hospital wards, patient rooms, environmentally controlled laboratories, or storage equipment environmental parameters (including temperature). Both humidity and humidity require continuous monitoring; in addition, the installation of portable devices is more convenient and flexible than devices that require external power and network cables. In some cases, if you need medical equipment that the patient carries with you, the temperature detection equipment of the cold storage, etc., you cannot connect the power cord and the network cable at all.

What kind of functions are required for portable medical devices? First, you must bring your own power. It can usually be powered by a rechargeable or non-rechargeable battery, although there are other ways (such as solar power), but this depends on the voltage and current requirements. Regardless of the power source used, the power supply must be efficient enough, and battery-powered portable devices should be able to enter "sleep" mode to minimize power consumption when not required to operate at full capacity. Sleeping devices can be externally triggered or periodically It is "wake up" and then increases the speed of the operation (of course, the power consumption will also increase) into the normal working mode. The device should also have some modes of operation between full-load operation and “sleep” mode to perform some simple tasks (such as accessing memory or refreshing LCD and LED display data), as devices are usually only under certain conditions. Full-load computing power (such as filtering and decoding sensor data) is required, so that a certain degree of balance between power consumption and operating speed can be achieved.

Portable devices do not always guarantee access to wireless networks, even if they support wireless communication. Depending on the network conditions, the device works in a wireless network environment at a certain moment, and may move to an environment without a wireless network at the next moment, or the wireless network may be temporarily shut down due to power failure. In these cases, if the device itself does not support wireless communication, the device needs to store the data collected at any time for future data upload to the upper system for data processing. There are some key data (such as environmental safety failure data, configuration data or device drivers) that must be secure for storage, even if the battery fails or is removed.

Other features of portable devices depend on the specific application requirements. Data can be collected directly through analog sensors or accessed through a local area network access subsystem. Portable devices can only passively collect data or actively voice alarms under certain conditions. Or send a signal to someone. Some simple data acquisition devices do not require user intervention before uploading data, while others (such as handheld blood glucose meters or wristband heart monitors) may need to change configuration or browse data through additional input and output devices instead of the host system. .

Designing a Portable Data Logger with the MAXQ2010

Although there are many microcontrollers to choose from in the industry, Maxim's MAXQ family of low-power mixed-signal RISC microcontrollers, the MAXQ2010, are ideal for designing battery-powered data acquisition devices. The MAXQ2010 features extremely low power consumption and a very high MIPS/mA ratio. It requires only a small battery current to support portable applications. The integrated 12-bit 8-channel ADC can capture many types of sensor data and supports many types of local serial interfaces. (such as I2C, SPI, synchronous/asynchronous UART), can be used to access the host system and serial port non-volatile storage devices, or to communicate with other subsystems in the device.

The MAXQ2010 can change the power consumption by dynamically adjusting the clock frequency according to the current task's computing power requirements. When it processes all the data and events, the portable device can enter the lowest power sleep (stop) mode until it is applied again. wake. The MAXQ2010's core voltage is only 1.8V, which greatly reduces power consumption. The 3V independently powered I/O can communicate with external high-voltage logic. If you want to use a single power supply like a 3V button lithium battery and you don't want to use dual power supplies, you can power the core voltage with a built-in integrated voltage regulator. In stop mode, the regulator can be turned off to reduce power consumption.

The MAXQ2010 can read data from sensors in a variety of ways. If you capture analog sensor data, you can use the built-in 12-bit multi-channel ADC to support 8-channel single-ended inputs. The data collected by the MAXQ2010 from an external sensor can be stored in the RAM powered by the backup battery or in the internal flash memory as needed. The on-chip 32kHz real-time clock (RTC) also works in stop mode, providing time stamps for data as needed. The MAXQ2010 can be implemented if the user is required to enter data or display information to the user. It has a set of general-purpose input/output pins (56 in the largest package) that can drive LEDs, read mechanical switch settings, or scan through rows and columns. The way to connect the switch matrix. The MAXQ2010 also has an LCD controller that can directly drive a 3V segment LCD, supporting up to 1/4 cycle of multiplexing (COM1~COM4), and its largest package provides 40 dedicated drive pins for 4x multiplexing. The mode can drive a 160-segment LCD display.

Design example of data logger based on MAXQ2010

Like many electronic devices used to collect or store data, the MAXQ2010-based data logger uses a USB interface to communicate with a host such as a personal computer. However, since the MAXQ2010 does not have a USB interface, we use FTDI's chip FT232R to implement USB and UART switching.

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