Hi everyone, I have recently brought an Arduino UNO R3 for my project that using MLX90614 to control 2 fans and showing the body temperature on a LCD 1604 screen. As what I seen on the website, I am pretty sure that the only suitable input voltage for usb is 5v. However, I am going to use 2 of 3.7V 18650 batteries with usb cables, which is total 7.4V, I am wondering if the processor and other components can support this voltage, thank you!
No; the specifications for the processor (328P) and serial-to-usb converter (16U2/CH340/...) in combination with the schematic of the Uno will make that clear.
You can use the 7.4V but you have to feed it into the barrel or Vin. In that case there are limitations on how much current the 5V pin can deliver to power other devices; fans (you did not specify which ones) directly powered from the 5V pin of the Arduino are basically out of the question.
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Okay, then I guess I will choose using VIN pin instead.
328P datasheet: https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-7810-Automotive-Microcontrollers-ATmega328P_Datasheet.pdf
16U2 datasheet: https://ww1.microchip.com/downloads/en/DeviceDoc/7799S.pdf
MLX90614 datasheet: https://media.melexis.com/-/media/files/documents/datasheets/mlx90614-datasheet-melexis.pdf
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2x 18650 to vin pin is a quick solution. But if you want to get max battery life , there are better ones. Battery voltage is not a fixed value, for two 18650 the voltage varies from 8.4V when full to 5V when empty.
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