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| TI烟雾检测器解决方案 | |||||
作者：TI 文章来源：本站 点击数： 更新时间：2007-3-19  |
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Ultra-low power, very low cost, high-performance smoke detector using a tiny 20-pin MSP430F1101. Design Considerations  The example demonstrates an ultra-low power, very low cost, high-performance smoke detector using a tiny 20-pin MSP430F1101. An IR-LED based smoke chamber is used to measure reflected light - if smoke is present, more light is reflected and seen on an IR-transistor. Temperature is measured using a negative temperature coefficient (NTC) resistor. The application operates normally in the MPS430F1101s stand-by mode, with all components shut down, except the MSP430s ultra-low 32kHz oscillator and a timer. The F1101s comparator A is used to perform an analog conversion on TIs low power TLV2760 OpAmp output using a form of sigma-delta (pulse density) modulation. A port pin provides a pulse density that matches that of the OPA output. This is a very accurate, low-cost method of measuring a voltage using comparator A. The temperature is measured using a form of dual-slope conversion comparing a capacitor discharge time of a reference resistor to that of an NTC, again using comparator A. Over 10-bits of resolution is possible. If the smoke is present and temperature is above a safe range, an alarm is issued. Because not all of the F1101s resources are used, it is possible for engineers to implement other features such as serial communication - including UART and Manchester encoding - using the timer A. In very cost sensitive applications, the 32kHz crystal can be removed and the application runs completely from the MSP430s internal DCO. The DCO can be trimmed to +5% using a single external resistor. |
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