Low power portable medical data recorder

Many medical applications requires no external power and data cable of the portable self-powered device, the most obvious example is the patients carry used to measure heart rate, body temperature and other health indicators of portable data recorder.

Of course, there are many complex applications even through external power supply, would need a small battery equipment secure redundant and equipment monitoring, such as hospitals, patient rooms, the environment controlled laboratory or storage device environment parameters (including temperature and humidity) continuous monitoring is required; the other portable device installation you will need an external power supply and network cable to the device easier and more flexible.

In some cases, such as the need for patients to carry medical equipment, freezer temperature detection equipment, no external power and network cables.

Portable medical equipment requirements which features? first, must be on-board power supply.

Usually available through rechargeable or non-rechargeable battery, although there are other ways (such as solar power), but this depends on the voltage and current requirements. No matter what kind of power supply, power supply efficiency must be high enough, and battery-powered portable device does not require a full load of work should be able to get to the "sleep" mode to minimize power consumption, dormant devices can be an external trigger signal or regular is "wake up", and then raise the operation rate (of course, power consumption will increase) in normal operating mode. The device should have between full-load work and "hibernate" modes of operation to perform some simple task (such as access memory or refresh LCD and LED display data), because devices typically only under certain conditions would need full-load operation capability (e.g. for sensor data filtering and decode), so that you can power and speed between a degree of balance.

Portable device even though support for wireless communication, but is not always guaranteed to be able to access the wireless network.

Depends on network conditions, a time machine in a wireless network environment, the next time it may be moved to does not have a wireless network environment, or may be caused by power outage temporarily turn off the wireless network. In these cases, if the device itself does not support wireless communication devices will need to keep collecting data stored for later upload to top level systems for data processing. There are a number of key data (such as environmental security failure data, configuration data, or device drivers) must ensure that the storage security, even if the battery fails or is removed or is missing.

Other characteristics of the portable device depends on the specific application requirements, the data can be directly through the analog sensor acquisition or through local network access to a subsystem read, portable device can only passively collecting data under certain conditions the voice alarm proactively through or to signal the alarm.

Some simple data acquisition equipment before the upload data without user intervention at all, while other devices (such as hand-held blood glucose meter or wristband-heart monitor) may require additional input and output device instead of the host system to change configurations or browse data.

Use MAXQ2010 design portable data logger

Although the industry has many options for microcontrollers, but Maxim company MAXQ series low-power microcontrollers, mixed-signal RISC MAXQ2010 characteristics that is ideal for battery-powered data acquisition devices.

MAXQ2010 have extremely low power consumption, high MIPS/mA ratio, only need a small battery current support portable applications, integrated 8 channel 12-bit ADC can collect many types of sensor data, and also supports many types of local serial interface (I2C, SPI, UART synchronous/asynchronous), can be used to access the host system and serial non-volatile storage devices, or relating to this device in the other subsystem communication.

MAXQ2010 according to the current task on computing capacity requirements by dynamically adjusting the clock frequency to change the power consumption, and when it has finished processing all of the data and events, a portable device to go to the lowest power consumption of Hibernate (stop) mode until you wake up again by application.

MAXQ2010 nuclear voltage only 1.8V, can greatly reduce power, 3V independent power supply of I/O can communicate with the external high-voltage logic. If you want to use as the lithium battery 3V button this single supply and do not want to use the dual power supply, you can use built-in integrated voltage regulator to nuclear power. In stop mode, the voltage regulator can be turned off to reduce power consumption.

MAXQ2010 to a variety of ways to read data from the sensor, if acquisition of analog sensor data, and can use built-in 12-bit ADC, multi channel support, 8-channel single-ended input.

MAXQ2010 from external sensors collecting data can be stored in backup battery-powered RAM or internal flash memory. On-chip clock based on real-time 32kHz (RTC) in the stop mode can work, according to the timescales for the data provider. If you want users to enter data or information that is displayed to the user is able to achieve MAXQ2010, it has a set of general purpose input/output pin (the largest packaging has 56), you can drive LED, read the mechanical switch settings, or scan through the ranks of the connected switch matrix. MAXQ2010 also has an LCD controller, you can direct drive 3V-segment LCD that supports up to 1/4-cycle multiplexing (COM1-COM4), its largest package provides 40 specialized driver pins, in 4 times the multiplex mode can drive 160 segment LCD display.

The data recorder based MAXQ2010 design examples

Like many used to collect or store data in the electronic device based on the data recorder adopts MAXQ2010 USB interface with the host (PC) communication.

However, because no USB interface MAXQ2010, we use FTDI FT232R chip company achieve USB adapter with UART.

Adopt the FT232R can give loggi design brings many benefits.

First, when the USB bus activity, The data logger can take advantage of the FT232R 3 .3V regulator output power supply, only one can be against diodes and battery-powered automatic switching, and because the regulator output (minus 0.2V diode forward voltage drop) voltage than the battery voltage after subtracting the diode drop in voltage high so that you can connect to the USB bus, the recorder no battery and power supply via USB Vbus. Takes two diodes (Figure 1) is to prevent a battery, output capacitor used to lower the load transient effect on the battery. Secondly, MAXQ2010 can utilize two serial interface (UART) in a direct and runs on personal computers, application communication, does not require any additional driver. Two serial ports by a built in USB connector on the virtual COM port connections. This design uses MAXQ2010 32kHz FLL based crystals as their own clock source (if you need to provide for RTC timing), it costs less than other crystals or resonant circuit costs are much lower. FLL circuit corresponds to a multiplier coefficient multiplier for 256, 32kHz Crystal oscillation frequency to 8.388MHz as MAXQ2010 clock.

Is calculated based on the data logger is MAXQ2010 consumes much current, can be considered: first, an external signal (such as buttons or sensors voltage jumps) micro-controller to wake from the stop mode; the system then through a single ADC channel read analog sensor voltage, the acquisition of sensor voltage values are stored in the data in RAM; at this point in order to save power, the micro-controller to return to the stop mode, but in about 60 seconds, the arousal of micro-controller was again (back in step 1).

Therefore, the calculation of the average current consumption and estimated battery life need microcontroller following parameters substituted the formula (1): tActive (complete all operations, including entering stop mode), iActive (this period of typical current values), tStop (keep stop mode), iStop (stop mode typical current), tExit (from stop mode is wake-up time), iExit (was woken by the typical current).

(tActive × iActive) + (tStop × iStop) + (tExit + iExit)

tActive + tStop + tExit

According to the above parameter values can be calculated from the average current of approximately 202nA; that is, if the power is an ordinary CR2032 lithium battery, the battery life can be estimated as 1138 hours.

Different battery manufacturers production of battery characteristics vary, CR2032 battery in 90% of discharge interval not exceeding 0.3V pressure drop, which means that the battery voltage drops to 2.7V before (after a diode drop back to 2.5V, meet single-supply operation at minimum voltage), micro-controller can work in 1024 hours.

Increased battery capacity or quantity, use rechargeable batteries, or when you are connected to the USB charging, etc. automatically while many measures are used to extend the battery life.

General average current is only slightly higher than the stop mode, the standby current, this is because the stop mode time far longer than the time the program runs, stop mode of the current play a leading role. Program loop code can be extended, such as measuring multiple sensor values or add other features do not significantly change the battery life. Of course, the use of other peripheral functions, such as LCD displays, LED indicates or serial port, and so will increase the power consumption, designers in the calculation of the actual battery life when you need to consider these features may increase power consumption.