I'm about to start porting a project of mine (http://speeduino.com) for the Teensy 3.5 and looking at making an adapter board that will allow the Teensy to plug into existing shield boards designed for the Mega 2560. For the most part this is relatively straightforward, but one area that does need more than simple physical connections are the 5v analog signals. Because this is going onto existing boards that are all operating at 5v I cannot simply change the source voltage for the inputs to 3.3v or anything like that.
To put it simply, is there any reason why a simple voltage divider is not suitable for something like this? The total impedance of the circuits with the divider will not exceed 20k, which I think should be fine for the Teensy, and the boards these are plugging into already have sufficient caps and transient voltage protection (I can be confident that input voltage will never exceed 5.1v at most). The readings will all be translated into an 8-bit range (ie 0v to 5v -> 0 to 255) which is then used against a calibration table, so the code itself should be trivial provided the signal itself is brought down to 0v-3.3v and not just cut off etc.
Is there anything I'm missing here that I need to be worried about?
To put it simply, is there any reason why a simple voltage divider is not suitable for something like this? The total impedance of the circuits with the divider will not exceed 20k, which I think should be fine for the Teensy, and the boards these are plugging into already have sufficient caps and transient voltage protection (I can be confident that input voltage will never exceed 5.1v at most). The readings will all be translated into an 8-bit range (ie 0v to 5v -> 0 to 255) which is then used against a calibration table, so the code itself should be trivial provided the signal itself is brought down to 0v-3.3v and not just cut off etc.
Is there anything I'm missing here that I need to be worried about?