This means your analog readings will be multiplexed or, if you prefer, they will share the same ADC circuit. You have many analog pins on your board, but there is only 1 ADC in your microcontroller. A common workaround for this is to perform two or more readings in rapid succession: each reading will give the capacitor a chance to equalize to the pin voltage, eventually bringing it to the desired voltage. If you try to measure the voltage of a low impedance circuit this has no side effects: the capacitor will charge/discharge very quickly due to its very small capacitance and your readings will be accurate.īut if you try to measure a high impedance circuit (like an LM35 temperature sensor), you must take into account the time it requires to allow the capacitor to charge/discharge.

This means the ADC is not reading the voltage at the pin, but the voltage at the capacitor plates! This might be higher or lower than the voltage you are trying to measure, due to ADC multiplexing (more on this later). The internal conversion circuit stores the voltage to be measured into a small capacitor (14pF in most cases) through a resistor, in the order of 10k Ohm. You can’t get around the 10-bit resolution limit (well, you can using averaging techniques, but that’s out of scope for now), but you can increase your resolution by reducing the reference voltage: a scale of 1024 applied to 1V means an increment every approximately 1mV, five times better. This is not bad for most projects, but definitely something to be aware of. This means our readings have a resolution of about 5mV and we will not be able to determine the difference between 1.000V and 1.004V. This conversion is never perfect and its precision is determined by the ADC resolution, in our case being 10 bits: we get a value between representing usually a voltage between 0V and 5V. The Arduino microcontroller (commonly an Atmega328 integrated circuit) is capable to convert analog readings into a digital value through its internal ADC (Analog to Digital Converter). I’ll try to keep the explanations as simple as possible, mainly for two reasons: keep the thing simple for beginners and avoid saying stupid things myself. While I believe those might be valuable, I believe they deserve a post as they have a broader range of application than the library itself. I’ve just published a small, open source, Arduino library to sense battery level in Arduino projects and, while writing the readme file, I found myself trapped explaining the reasons behind some decisions.

Arduino read analog voltage