Same concept, but I am using 10k and 22k resistors.
I just was not sure about there only being one wire in my case.. or do I need to find a ground from the device as well?

I have a single wire that reads either 9.25 volts or -50 mV when it is toggled on/off. I would like to read the on/off via GPIO input, but I am getting false positives with a voltage divider. Can anyone help with another option or with an example wiring diagram for how it should be wired? Any help i...

Thanks again sprinkmeier. I think I understand. Using the voltage divider circuit (similar to the ultrasonic module image above), I simply can add a 3V zenner to provide some protection.. And to do that, I just need to jump it across the RasPi GPIO and RasPi GND? Otherwise, I can use an optocoupler....

Thank you for the info sprinkmeier.

The device itself runs on 24v, but I am using a single wire that either has 0v or 9v to signal if something is over the sensor. With the voltage divider (10k and 22k) resistors, what could it handle at most? 9v?

The voltage divider works great.. thank you! It reduced the 9v to 2.8v and triggers the gpio input correctly. Do I also need to run the ground wire from the device (as I do with the 9v battery)? Also, what if there is a spike in voltage from the device over 9v? Do I need something like a optocoupler...

Thank you Pluggy. Would it end up something like the image below? But, I would swap the "Echo" with the positive end of the battery, and the negative would be the "Ground" on the module in the image? (R1 would be 22k and R2 would be 10k) Thanks again for your help. Ultrasonic-Module-Circuit-e1356208...

Yes, the LED circuit can be connected to the pi. If there is a better solution to detect the 9v, I am also open to that as well.

I simply have one resistor between the + end of the LED and positive end of the battery. It drops it down to around 2.2v. The reason I am using 9v is because in this particular application, there is a device that either has 0v or 9v in the line to signal a 1 or a 0 that I need to be able to read. Wh...

Is it possible to use a GPIO input to tell if a LED is on or off? It is separately powered from a 9v battery in this example.

GPIO.setup(pin, GPIO.IN) is giving me false positives. Any help is appreciated!

I have a photo sensor that I would like to hook up and read using the Pi. I am just not 100% clear on the wiring and if it will work. It states the supply voltage and current is: 20 to 250V ac (50/60 Hz), average current is 20 mA and the pead current is: 200 mA @ 20V ac, 500 mA @ 120V ac, 750 mA @ 2...

I would like to be able to control a zone stop on a piece of conveyor using a raspberry pi. The module on the conveyor: "is equipped with terminal block connections to accept a zone stop signal from a switch, PLC, etc. This built-in feature will allow any zone to become a workstation zone or an “int...