The analog inputs only allow 0 to 5 volts. How do I measure an analog signal which ranges between -5 to 5 volts? Offset the signal by +5 volts and then divide the signal in half? How do I do that without using op amps?
Use a 1:1 voltage divider, with the other end connected to +5V. For example:
10K resistor between input to be measured and Arduino analog input pin
10K resistor between same Arduino analog input pin and +5V
Then the Arduino input voltage will vary linearly between 0V and +5V as the input varies between -5V and +5V.
You can use a resistive divider if your voltage source is low-impedance.
two 10k resistors make a divide-by-2 divider, one end goes to +5V, the other to your input, and the
centre point to the analog pin.
Then an input of -5V will yield 0V at the analog pin, +5V will give +5V, and 0V in gives halfway, 2.5V.
Of course the voltage source has to be able to cope with the 20k load resistance of the divider - what is it?
Thanks guys! 