因為使用Arduion 做為電池容量測試的工具並以電腦做為長期資料收集的後端。因為Arduino 吃電腦USB的電，所以Arduino無法使用內部的參考電位做為ADC的參考電壓。必須要額外使用一個穩定和足夠精準的參考電壓，來做為ADC 的校正。這樣才能保證ADC計算出來的電池電壓值的精確度在一定的範圍內。便宜方便的做法是使用一顆TL431，它的2.5V的電壓輸出，做為ADC自我校正的參考電位。其電路如下圖所示:
這個參考電壓電路只要一顆TL431與一顆電阻的組成，就可以得到一個穩定的2.5V的參考電壓。input 接Arduino的VCC, Vka就接到ADC的輸入做為校正電壓。
另外如果有精度更高的需求，可以使用更好的參考電壓原件，比如 ADR3425。
The circuit on Figure 1 is used to get a reliable and stable reference voltage. Usually the ADC will not be accurate when Arduino connected to PC via USB. If we want an accurate ADC/voltage mapping, we will need an accurate and reliable reference voltage to calibrate AD value. The figure 1 is a sample solution. The VKA is a stable 2.5 voltage output. The MCU can use it to calibrate the ACD/Voltage mapping.
The circuit on Figure 1 is used to get a reliable and stable reference voltage. Usually the ADC will not be accurate when Arduino connected to PC via USB. If we want an accurate ADC/voltage mapping, we will need an accurate and reliable reference voltage to calibrate AD value. The figure 1 is a sample solution. The VKA is a stable 2.5 voltage output. The MCU can use it to calibrate the ACD/Voltage mapping.
