Inverted transistor?

Hey all, I'm pretty new to Arduino and all that but I've been searching online for a while now and can't find what I am looking for so I'm gonna ask here if it exists.

What I'm trying to do is actively block a connection between something on a different grid than the arduino but if I connect a transistor between them the arduino has to be constantly plugged in for it to work and allow the connection. What I need is sort of an inverted transistor where it always allows the connection until the gate pin is hit with a high signal and then the transistor cuts off the other grid's connection. But I can't seem to find a way to do this.

If you want schematics or something I can make those easily but I don't find it quite necessary so I'm not uploading it with this post. Just ask if you need one.

Thanks in advance to whoever can help! I hope there is a way to fix this.

You can use a gate pull up or down resistor, to obtain its default (on?) state. Then the Arduino output applies the opposite signal, to turn the transistor off.

But how would the pull up/down resistor retain the on state if it had no power? I cannot connect anything to the same grid the transistor is controlling, the current is much too powerful. And if the arduino is off I don't see how a resistor could be powered. Sorry if I misunderstood something. I'm going to read more on pull up/down resistors now.

If there is no power there's nothing for that transistor to switch, so it doesn't matter.

I think you should provide us with a schematic explaining a bit more what you're trying to do. There are many ways of switching things on and off using different types of transistors.

MOSFETs are great because they have almost zero resistance when on. BJT transistors don't exactly have resistance but they do have a voltage drop. If you're just building one, you don't care if you are paying $1 or $0.50 so go with the more expensive MOSFET.

A P-type MOSFET can be wired to control a positive voltage. Once again, more expensive than the more-common N-type but immaterial for just one or two.

Here's my favourite tutorial: MOSFET as a switch.

However, for the Arduino to control a P-type at a high voltage (you didn't say how high) it can't be connected directly. Often it is easy to use an N-type to control the high voltage.

You can also go for the rare depletion-mode MOSFET which is always on unless you turn it off, but there are very few tutorials online which actually give you useful details like part numbers you can actually order.

You want a transistor (or some equivalent) to act like a relay with normally closed contacts? Only when power is applied to it (its coil) will the circuit be broken. Maybe give more details about the device you are connecting to.

I think we are all missing something here guys, he said:-

What I’m trying to do is actively block a connection between something on a different grid than the arduino

Does that mean the two signals do not have a common ground? If so you cannot do it without something like an optically coupled FET. Or an analogue switch on the device side being fed by a conventional opto isolator who’s output is pulled up to the pass through logic state.