Do you guys know of anything we can use to prevent back feeding current besides a diode?
We have the signal acceptor(frequency in hz) on an arduino uno that requires a lift with a 4.7K resistor to 5v to bring the signal up from 0V but the signal source also needs to feed into a computer and we don't want the voltage lifted signal to go to computer (not sure if it will fry). We tried putting a diode in which blocked the 5v back flow to the computer but the arduino no longer got a proper signal and didn't read correctly as I assume the diode is somewhat rectifying the signal. So we just need a circuit or component that will prevent the back flow and let the signal run clean through. Thanks in advanced for the help!!
Not enough info for a proper answer.
Most Arduino variants use backflow protection.
A Nano uses a simple schottky diode, and an Uno/Mega uses a p-channel fet.
Schematic diagrams can be found on this site.
Leo..
there are 3 files attached one is the raw out put signal on a scope, another is the 5v pullup on the scope and another wonderful microsoft paint diagram of the whole works, i think drew the diode in correctly. on the project i just connected the diode to the ardiuno side of things (and 5v pullup) powered it up and then tested with my multimeter on the sensor side and flipped it to the direction where the meter read 0v and not 5v. looking at the scope out put (found online same sensor similar project) it occurred to me that i might not need to worry about the 5v pull up. and looks to me (not sure) that the sensor in its raw form outputs a 0-9.86v squareish wave and when the pull up resistor is attached it some how brings the signal down to a 0-2.28v square wave??? also mentioned is that the sensor is an open collector output not exactly sure what that means. and my interpretations of the scope readings are from my freshman year of high school so feel free to correct me if im wrong.
An open collector is supposed to draw current through the pull-up resistor (when the output goes low, "overpowering" the pull-up). And you shouldn't be getting 9V unless you've got 9V through a pull-up... And, without something pulling-up an open-collector it won't go up.
here is the last scope reading with the 5v pull up, if that is how an open collector works its very well possible that the computer (ecu) has a pull up built in, i will test the input on the computer and get back, hopefully the computer pull up isnt over 5v or i suppose i will need to play with resistors to get the voltage back down to 5 for the ardino to measure.
A safe way is a (1N4148) diode between Arduino pin and device output, with the cathode (ring) to the device.
With internal pull up on the pin (or external 1k pull up in noisy environment).
Note that there is no "0-4.5volt output" on an Arduino. It is 5volt PWM.
Leo..
