You will find that the way you have built your if-elseif statements won't work quite as you expect:
if (value >= 0) {
//value is always greater than zero, so code always reaches here
if (value <= 5) {
...
}
} else if (value <= 209) { //about 1 v
//The first if statement is always true, therefore this bit of code never executes.
if (value >= 200) {
...
}
}
You are along the right lines though. You just need to consider what you are looking for. For the first if statement you want the value to be >=0 AND <= 5. So based on that you get this:
if ((value >= 0) && (value <= 5)) {
... //will execute if the value meets both conditions
} else if ((value >= 200) && (value <= 209)) { //about 1 v
...
}
The problem of negative values however still remains. What you need to do is to take your +/-1v signal and add a bias so that it is within the range of the ADC.
There is one such method which uses just two equally sized resistors. I have attached a schematic.
What the circuit does is att 2.5v onto the signal meaning that when you have -1v, the ADC sees 1.5V, when you have +1v, the ADC sees 3.5v.
How successful this method will be depends on what is driving the +/-1V signal.
