Hi all,
I'm building a variable power supply and i'm currently working on the current measuring system. I need to measure 0-3A fairly accurate, down to mA. In other words i need 3 positions after the decimal point (for example 2.455A). The value will be displayed on a LCD screen so i will be using a AVR microcontroller. My idea is to pass the current through a shunt resistor and i want the maximum voltage drop on it to be no more than 20-30mV.Than use a low offset voltage op amp (offset in the microvolts range) to amplify that voltage drop to some usable value for the microcontroller ADC. The problem is that im don't know if the microcontroller ADC will have good enough resolution and accuracy for the job. It's a 10bit ADC, so 1024 steps. Another way will be to use an external ADC chip with a 16bit resolution. What do you think of that ? Is there a better way? I was looking at hall effect current sensors like ACS712, but they don't have the accuracy for the mA range (1.5 percent error). Are there any other prebuild chip solutions? I don't really need spot on accuracy, let's say -+1-2mA is ok.
I'm building a variable power supply and i'm currently working on the current measuring system. I need to measure 0-3A fairly accurate, down to mA. In other words i need 3 positions after the decimal point (for example 2.455A). The value will be displayed on a LCD screen so i will be using a AVR microcontroller. My idea is to pass the current through a shunt resistor and i want the maximum voltage drop on it to be no more than 20-30mV.Than use a low offset voltage op amp (offset in the microvolts range) to amplify that voltage drop to some usable value for the microcontroller ADC. The problem is that im don't know if the microcontroller ADC will have good enough resolution and accuracy for the job. It's a 10bit ADC, so 1024 steps. Another way will be to use an external ADC chip with a 16bit resolution. What do you think of that ? Is there a better way? I was looking at hall effect current sensors like ACS712, but they don't have the accuracy for the mA range (1.5 percent error). Are there any other prebuild chip solutions? I don't really need spot on accuracy, let's say -+1-2mA is ok.