If there is a current running through a wire, I need to apply battery voltage to a different wire. The wire I need to monitor with a Hall effect is 16v DC. I can't cut into that wire. If there is a current running through the monitor wire I need to apply 16v to an output wire. Can someone please help me figure out what I need to do this?
To do this you need a 16V power supply. Connect the output pin to a 1K resistor and the other end to the base of an NPN transistor. Connect the emitter of the transistor to ground, and the collector to a 1K resistor. Then the other end of the resistor to 16V.
You can't detect DC on a wire you can't cut. A Hall effect sensor will not be able to pick this up unless you have a serious amount of current flowing through the wire. How much is this?
If you could get the current flowing through a coil then you could detect the magnetic field from this coil. But the magnetic field a single wire generates is minuscule.
What sort of Arduino are you using?
Your title:
if-voltage-is-present-apply-voltage-to-different-wire
Your question:
If there is a current running through a wire
So which is it? Voltage or current?
What are you actually trying to do?
How much current?
Hi, @docfxit
Welcome to the forum.
Can you please tell us what the device you are going to measure the current from is and what you are aiming to apply some battery volts to.
Thanks.. Tom.. 
That's really great of all of you to reply to my request.
Thank you all...
I'll try to answer your questions. If I don't, It's not because I'm ignoring you. I'm happy to give you what ever I need in the way of details to get this put together.
I'm working with a Tesla model Y 2022. The low voltage battery runs on 16v. I'd like to install a Dash Cam Viofo 4K A229 Pro 3ch. I can tap into the trailer controller pigtail that I purchased from Tesla to power it with 16v. It normally runs off of 12v. I bought the HK Hardware Kit to hardwire it so it will accept the 16v. What I would like to accomplish is getting it to recognize when the car is parked. In a gas car they use the ACC to detect the car isn't running because there is a change in the voltage when the car turns off. I have contacted Viofo and they have no idea how get it to recognize the car is parked. When I put the car into park it energizes the parking solenoid on the rear wheel. I don't want to cut the wire because that would be a safety hazard. When voltage is applied to the parking solenoid, I'd like to apply voltage to the parking wire for the dash cam so it can go into parking mode.
I currently don't have any components. I am hoping to get a suggestion here as to what I should get and where the best place to get it is. If I haven't answered everyones questions please let me know. I'm happy to get the help in getting this working. If the parking solenoid doesn't work out, I could use Sentry Mode
to determine when the car is parked, if I could find the correct wire. Any and all suggestions are welcome.
Sounds like a job for relay...
Is the 'parking solenoid' permanently operated when parked or just momentarily in order to apply the parking brake?
I ask because I'm thinking it makes a difference to what happens next:
- Maybe the dash cam needs a permanent input or a momentary input, either way this needs to match what you do. If what the dash cam requires and what happens with the parking solenoid are both the same then it's a lot easier than if they are different.
How much current does a 'Dash Cam Viofo 4K A229 Pro 3ch' take?
I ask because I wonder if it's even worth putting it into parking mode. Is this just a current saving thing or is there more to it?
Change from what voltage to what voltage? It might be enough to use a voltage divider (2 resistors) to go from 16V to whatever voltage the dash cam needs to change mode.
I don't have a Tesla, but I've been in one and driven one and I was under the impression they had lots of cameras already, so I find myself wondering what the point of all this is.
EDIT:
While I was typing @kmin suggested a relay, I agree, but the answers to my questions might change that.
Thank you for your input. The Tesla has 8 cameras. The problem with using the Tesla cameras is the resolution isn't good enough to read a license plate. Also the Dash Cam has a wider field of view. Also the Dash Cam records what is going on inside the car. There are three cameras. I would like to use this for Rideshare driving like Uber. Also the Dash Cam records audio.
I'm not concerned about saving power. The main problem is getting the Dash Cam to know when the car is parked.
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The answer to Perry's question will help in figuring out how to detect the signal on the wire to the parking brake.
If you wrap a coil of wire around a conductor, current will be induced in that coil when current flows through the conductor. If that induced current is applied across a resistor there will be a voltage drop, the analog input on an Arduino could be used to detect that voltage.
I don't know whether this would be practical, my advice would be to try it and see.
Note that it has to be a single conductor, if you have a pair of conductors that complete a circuit, wrapping both of them creates no induced current because the net current through them is zero.
Sorry to tell you this but that's not true. For there to be any current induced in the second wire the current in the first wire has to be changing, not just flowing. Transformers only work with AC.
That's right. You could in theory detect the change when park is engaged.
If it is a permanent connection, then perhaps you could measure the magnetism that it creates with an analogue hall effect sensor.
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Consider the IMU of a Nano 33 BLE or BLE Sense - if the Accel and/or Gyro indicate a body at rest for a period of time then the assumption is 'parked'.
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That sounds like a perfect solution. That will save me from running more wire in the car. And it will remove any question of voiding the warranty on the car. Which one should I buy. Is there a good box I can get to protect it in the car. Where is the best place to buy one? What will I need to buy with it so I can power it from the car 16v?
You can buy them from the Arduino store.
A BLE Rev 2
Arduino Nano 33 BLE Rev2 — Arduino Official Store
It can run from 16V - but I don't know how "clean" that is coming from the car. It's an electric vehicle, so maybe it's not subject to all the nasties that can be encountered otherwise.
If there's a USB jack available then you could use that.
If it's in the vehicle all you need, I guess, is something to keep it out of trouble (a typical 'project box').
I was thinking the same principle would apply with a GPS. There's a data field for 'speed over land' (VTG) and if that's '0' for a period of time then the implication is - parked (most probably).
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It appears I need to reduce the 16v from the car to power the Arduino 4.8 V to 4.96 V. What should I buy to reduce and maybe regulate the voltage. Although I can't imagine noise in the car but I don't think they are that expensive. A link would be great so I get the correct component.
No. The Nano33BLE has a built in MPM3610 buck converter. You can power the Arduino with 16v on the Vin pin.