I'm trying to make voltage readings of several batteries that are common positive connected. Is there any way to make floating analog inputs ? i.e to measure the input voltages not referenced to the chip ground.
Thanks
Attached sketch shows the 2 test points. They will be used to control supply to the batteries.
Those voltages are below ground so you can't connect them directly to an arduino. You could however use an op-amp in an inverting amplifier with a gain of one to get the signals the right way up but you will need a split power supply for the op-amp.
After a bit of thought I came up with using an opto coupler 4n25.
I'll hopefully attach the sketch to another message due to it's size.
The reason for the common positive is that I'm using power mosfets to switch on and off
supply to the batteries. It's easier to provide the gate volts that way.
It's part of a project to convert my existing analog controller that lives in our 4WD, it
controls charging of an auxiliary battery and the vehicle battery (when camped up)
and some power outlets for charging other stuff. The system uses solar power mainly
but can utilise the vehicle power and a PSU if needed.
Cheers ........ Mike B
When you have. ref does that mean an analogue input?
The problem with this is it is not very linear, do you need an accurate measurement?
Yeah, the reference goes to an analogue input. (12v gives around 2.5v)
I'll be using the 5v reg ref as supply to the transistor.
I'll just read off the binary values when it's working and plug them into the code.
I only just need to know terminating and commencing points of charge so I'll
give it a try and see what happens. It may well be heat sensitive so I'll do some
field tests on one.
Thanks for the interest.
Cheers .......... Mike B