Hi folks,
I need to input voltage to the analog input of arduino referenced to 3.3v, problem is the source is current. I look at op-amps and find they need +5 and -5 , the arduino board only supplies +5 and ground. How can I do this? Is there another way to wire the sensor to get 1- 2.5v, from a variable resistor sensor?
How much current are we talking about? In general, a simple resistor creates a voltage drop when current flows through it.One side of it connected to ground, that’s as simple as it can be. Or perhaps a resistor divider might be in order. But it might be better also if you tell more about that ‘variable resistor sensor’ or whatever circuit you have.
Thanks Valen, I’m using a 5V pressure sensor, single pole to ground with variable resistance from 250 ohms to 40 ohms. I could divide the voltage with resistors to 3.3v but if I use 5v I can plug it directly in the Arduino A/D input. I was using a passive current to voltage circuit as per figure 2: http://en.wikipedia.org/wiki/Current-to … _converter. Worked fine but caused problems with communication for some reason, when I disconnected the sensor, I had no problem with connecting to the arduino. I even think I fried something inside, maybe too much current in the A/D pin. I’m considering an opamp but supply is a problem. Maybe a converter chip can give me -5v from +5v/G…?
I would prefer to use the passive converter since precision doesn’t have to be perfect, just consistent.
Which sensor are you using?
An oil pressure sensor.
You don’t want to be any more specific than that? A datasheet would be nice.
Thanks, as Valen said, a voltage divider will suffice, with a reference voltage, should do the trick… 
Sometimes I tend to go overboard with complications.
Okay that’s fair. I like to explore those options too, its fun to at least evaluate them in your head. Honestly I didn’t really understand what your sensor was doing at first which is why I asked for the datasheet but after reading it now it makes sense what you’re trying to do.