Hi,
I am currently trying to build a simple voltmeter for a school project with Arduino Boards. Therefore, I bought some ADS1115 ADCs with a decent resolution and sample rate. Since they only support input voltages of up to their supply voltage (3.3V in my case) and I would like to cover a higher voltage range (25V), I am planning to build some kind of voltage divider for the input.
Now I realize that students might fry the circuit if they connect the input voltage in reverse (which can't be avoided).
As far as I know, there would be two ways to resolve this issue:
-You install some kind of reverse polarity protection
-You make the system capable of measuring negative voltages (which would be the preferred way)
I am now asking myself rather i can just use the differential mode or if I have to build another voltage divider to shift the ground level of my input of (VCC/2).
Can you give me any advice on that? If possible, I would prefer to use the differential mode.
Agree that multimeters are more suitable (although students will probably fry the ammeter function in most cheap multimeters). Plus students should know how to use a multimeter.
Simple DIY Voltmeter/Ammeter is a great project for intermediate students though, especially if you have access to a 3D printer to make a case. An INA219 breakout board/OLED/Nano with a switch to change the gain/range is suitable for simple DC purposes.
Alright, some information for everyone with the same question:
I am using the module now in differential mode and with a voltage divider. As a result, it can measure positive and negative voltages within the desired range.
I was quite confused about the differential mode capabilities, but as I can now confirm, the pins seem to handle "negative relative voltages". Important: You cannot connect your measurement inputs to the module ground...
If you measure differentially using the default config for pins 0 and 1 then
AINP = AIN0 and AINN = AIN1
The voltage measured is AINP - AINN.
AINP, the voltage on pin 0, is considered the "positive" and AINN, the voltage on pin 1 is considered the "negative".
If the voltage on pin 0 is greater than the voltage on pin 1, the measured voltage AINP - AINN, will be positive. The voltage on pin 0 can also be less than the voltage on pin 1 in which case the measured voltage AINP - AINN will be negative.
This is not the same as applying a negative voltage to a pin. The datasheet gives the absolute maximum input voltages on any pin as: