基于usb總線的溫度監測器

　　使用模擬單片機，和LDO，外部熱敏電阻，和幾個分立器件，可以構造一個高度精確的溫度傳感應用。

　　圖1中的電路是模擬設備aduc7122精密模擬微控制器可用于精確的熱敏電阻溫度監測中的應用。的aduc7122集成了多通道12位SAR ADC，十二個12位DAC、一個1.2 V的內部參考，以及一個ARM7內核，126 KB的閃存、8 KB SRAM，以及各種數字外設，如定時器，UART，SPI，I2C接口和兩。的aduc7122連接到4.7 KΩ熱敏電阻。

　　Figure 1： ADuC7122 used as a temperature monitor interfaced to a thermistor （simplified schematic， all connections not shown）。

　　Due to the small form factor of the ADuC7122 （7 mm × 7 mm， 108-ball BGA package） the entire circuit will fit on an extremely small PCB， thus further reducing cost.

　　Similar in function to an RTD， thermistors are low-cost， temperature-sensitive resistors and are constructed of solid semiconductor materials， which exhibit a positive or negative temperature coefficient. Thermistors are inexpensive and have high sensitivity. They detect small variations in temperature， which could not be observed with an RTD or a thermocouple. However， thermistors are highly nonlinear; thus， they are limited to applications with very narrow temperature ranges if linearization techniques are not applied. Circuit linearization techniques can be accomplished in software.

　　Despite the powerful ARM7 core and high-speed SAR ADCs， the ADuC7122 still provides a low-power solution. With the ARM7 core running at 326.4 kHz and the primary ADC active and measuring the external temperature sensor， the entire circuit typically consumes 7 mA. Between temperature measurements， the ADC and/or the microcontroller can be switched off to further minimize power consumption.