View Full Version : teensy 3 adc voltage input max?

11-26-2012, 06:55 PM
while waiting for my teensy 2s to arrive i want to check out my input testing on the 3 that i have. i am using ratiometric hall effect sensors for input which really like to run on 5 volt minimum. they can produce as much as 5 volt output. i need to connect this to an analog input to eventually use this as a joystick axis control.

the question is whether the analog inputs are 5 volt tolerant. they are on my chipkits so i am used to this but can not find any real mention in the chips docs. there is a mention elsewhere of using a 10k current limiting resistor for other inputs. should i do this or should i just use a voltage divider ? if the ADC can't discriminate between anything over 3.3 volts, i might as well knock it down to 3. will experiment with scaling and resolution issues in the program but would like the widest range possible. if the ADC will give me values over a 5 volt input range that would be best.

don't want to burn anything up so hopefully i will get an answer about 5 volt tolerance quickly.

11-26-2012, 07:38 PM
I'd run the output through a simple voltage divider. For example, 4.7k and 4.7k gives you a max output of 2.5V, well within the safety limits of the chip. You can then refine further, either by setting the AREF to 2.56V or supplying an external AREF voltage. See the data sheet, I believe that anything over 3.6V will lead to damage, on any pin other than the voltage regulator input.