恆溫蓮蓬頭溫度監控系統設計

Abstract

中文摘要 本專題以「恆溫蓮蓬頭之溫度感測器設計」為主題，研究動機來自家庭淋浴時因其他水龍頭同時開啟，導致冷水壓力下降，使蓮蓬頭出水溫度突然升高，進而造成使用不適與燙傷風險，為提升家庭衛浴使用安全，本專題聚焦於出水溫度的即時量測與顯示，並不討論冷、熱水比例控制。系統主要量測範圍設定為 30°C〜50°C，感測器耐受範圍約為 0°C〜80°C，解析度目標為 0.1°C，準確度目標為±0.5°C〜±1°C。 在感測器選型方面，本專題比較 Pt100、AD590 與 NTC 熱敏電阻後，選用10kΩ NTC 防水熱敏電阻探頭，原因為其靈敏度高、反應速度快、成本低，且容易取得防水封裝形式，適合蓮蓬頭潮濕與水流噴濺環境。轉換電路採用分壓式電阻對電壓轉換電路，並以 5V 作為參考電壓，搭配 5.6kΩ 精密固定電阻，使 30°C〜50°C 範圍內輸出電壓約由 2.05V 上升至 3.05V，平均靈敏度約為 50mV/°C。 為避免後級電路影響分壓輸出，系統選用 LM358 作為電壓隨耦器，進行阻抗轉換與訊號緩衝。 指示電路方面，本專題規劃以 ADC 讀取 LM358 緩衝後的電壓訊號，再透過程式換算成溫度並顯示於 LCD、OLED 或其他顯示元件，同時可加入 LED 或蜂鳴器作為過熱提醒。為提高量測穩定性，電路設計中加入 0.1μF 旁路電容、RC低通濾波、導線防水與屏蔽處理，以降低電源雜訊、長導線干擾與潮濕環境造成的誤差。最後，本專題提出調校步驟與採購建議，透過多點溫度校正、電壓量測與查表修正，使系統能更準確地顯示蓮蓬頭出水溫度，達到安全、防燙與即時監測的設計目標。

Abstract This project focuses on the design of a temperature sensing system for a thermostatic showerhead. The motivation comes from a common household situation in which the shower water temperature suddenly increases when another faucet is turned on, causing a drop in cold water pressure and changing the original hot and cold water mixing ratio. Such a sudden temperature rise may cause discomfort or even increase the risk of scalding. Therefore, this project aims to develop a sensing unit that can measure and display the shower outlet water temperature in real time. The scope of this project is limited to temperature measurement and indication, and does not include the control of the hot and cold water mixing mechanism. The main measurement range of the system is set from 30°C to 50°C, which is close to the normal showering temperature range. The sensor tolerance range is approximately 0°C to 80°C, with a target resolution of 0.1°C and an accuracy target of ±0.5°C to ±1°C. After comparing Pt100, AD590, and NTC thermistors, a 10kΩ waterproof NTC thermistor probe is selected because of its high sensitivity, fast response, low cost, and availability in waterproof packaging suitable for humid bathroom environments. The conversion circuit adopts a voltage divider structure using a 5V reference voltage and a 5.6kΩ precision resistor. Within the 30°C to 50°C range, the output voltage is estimated to increase from approximately 2.05V to 3.05V, with an average sensitivity of about 50mV/°C. An LM358 operational amplifier is used as a voltage follower to provide impedance conversion and signal buffering. The buffered voltage signal can then be read by an ADC and converted into temperature data for display on an LCD, OLED, or other display module. In addition, an LED or buzzer can be added as an overheating warning device. To improve measurement stability, bypass capacitors, RC low-pass filtering, waterproof wiring, shielding, and calibration procedures are also included. Through multi-point temperature calibration and table-based correction, the system can provide a safer and more reliable shower water temperature monitoring function.