ADC voltage

[MitchW]

I am even less then a newbie. This is my first post, and I do not currently have a IsoPod. Depending on what I find on this forum, I may get one for a project. My other disclaimer is that I AM NOT HARDWARE LITERATE! I may be turning to this source for very simple hardware help. The IsoPod seems to have a great level of integration, which should minimize the amount of hardware I will have to build.

My questions has to do with using the ADC. What do I do if I need to use the ADC with a 5V device? The device requires 5V to work, and the value to be measured is in the 0 to 5V range. What do I do?

Thanks for any suggestions.
Mitch

[RMDumse]

Fortunately, this is a simple hardware problem to deal with. If you have an input signal that varies from 0 to 5 volts, you can use two resistors in series to divide the voltage down to a lower range.

Let's say we use a 2K and 3K resistor. Put the signal to be measured into one end of the 2K resistor. Hook the other end of the 2K resistor to one end of the 3K resistor. We'll call this the junction of the two resistors. Put the other end of the 3K resistor to ground.

Using two resistors like this is called a "resistor divider".
The relative size resistors you pick, determines the division amount. The total resistance of the two resistors determines the impedence of the input, which means how strong the signal has to be to push the divider. 2K and 3K will require a signal source to supply 5V at 1 milliamp, so that's a pretty reasonable couple values to use.

Also since the total resistance is 5K (2K+3K) the ratio of the division will cause the junction to range from 0 to 3V when the signal put in goes from 0 to 5V. Perfect. Just what you need. So a wire goes from the junction to the 0 to 3V inputs on the IsoPod.