Basic Arduino Circuit

Hey Everyone,

So I am extremely new to Arduino but I have a decent knowledge with programing and circuitry theory. I do not have a lot of experience building circuits since I’m a mechanical engineer but the project I’m working on will require basic circuits to be built in conjunction with the board.

My issue is relatively simple. Basically I want to have 5 wires attached to the Arduino board with 5 volts going though each of them. If one of these wires were to be cut, I would like for the Arduino board to notify me by flashing an LED. I need this to happen for every time a wire is disconnected from the 5 volts it is receiving from the external power source.

My question to you is which Arduino board would be best for this project? Also, which ports do you connect each individual wire to on the Arduino board so that it can scan them all and check if current is still be carried.

Attached is a very … very basic diagram of what i am explaining.

Thanks for your help!

Any of the Arduino I/O pins will do. You can use digitalRead(ppp) to read any of them - ppp is the pin number.

It may be easier if you set the pin as inputs using the internal pull-up resistors (pinMode(ppp, INPUT_PULLUP) and connect the other ends to ground rather than to 5v.

If you must connect the other ends to 5v you will need to use external pull-down resistors at the Arduino end to make sure that the voltage at the pins goes low when the wire is cut. In this case you would just use pinMode(ppp, INPUT). Without the pull-down resistors the voltage on the pins will float and won't give reliable readings.


Great that helps a lot thank you. But yes I was curious about connecting the ends to a ground. Id rather connect the wires to a ground which will be possible. Does this mean the Arduino is passing a current though each wire? if so how will it be notified if a wire is cut then?

Also which board would be best for this and lets say if i wanted to use 160 connections?

Sorry for the lack of terminology.


Yes, with pull-up resistors engaged, very small currents will flow through the wires to ground. These currents drag the Arduino inputs down to 0V. If the wire is cut, the inputs are no longer dragged down and instead the pullups drag them up to 5V.

No Arduino has 160 inputs afaik. Therefore you will need extra circuitry, for example (de)multiplexers, shift registers... tell us more about the purpose and nature of the 160 wires and we can advise further.


ACRocco13: how will it be notified if a wire is cut then?

Just to clarify, the Arduino isn't notified as such, as in a flag waving.... The structure of Arduino code is that the loop() part runs again and again, very quickly. In that loop you will have a series of digitalRead() statements, one for each pin of interest. Those pins are then read sequentially over and over very quickly, and with the internal pullups mentioned above, you'll be looking to see if any pin is low.

Thanks for all the help guys. This making sense

The basic reason for the 160 wires is that I plan to make a mesh of 80 vertical wires/80 horizontal wires. The plan is that when something passes thorough this mesh it will cut the wires and notify me of this occurrence each and every time. I refer to wires because that is how I plan to prototype with to ensure everything functions properly. Eventually id like to have this mesh made of E Ink or flat copper wire pasted to a pice of card stock.

If anybody has a better or more efficient way of doing this id be very interested

Sounds like an expensive system if the wires are going to be destroyed every time.

Is it possible to do it with beams of light?

How precisely do you need to locate something?

What is going to break the wires? - I hope this has nothing to do with guns !


I thought of light beams but I do not feel that this would work. I plan to mesh the wires in a 8 by 8 inch square for starters.

I first just wanted to try with 5 wires to make sure the system works and my programing is correct. From there i would expand to make it into a much larger mesh.

Robin2-why do you hope this has nothing to do with guns?

It doesn't necessarily need to be precise. It just needs to signify if it passes though and 8 by 8 inch square multiple times

Robin2-why do you hope this has nothing to do with guns?

Quite simple. I object strongly to guns.


light should work although you might be better off using discrete electronics to detect each channel. the beauty of light is that it will reset itself at something on the order of a pico second.

a falling water droplet would pass the light grid, and report the location of each consecutive droplet.

Guns are like knowledge or medicine or electronics. in the right hands, brings hope and safety. Why else would the governments want to keep vast arsenals ?

Robin I understand and I respect that

Dave-I know what you mean about light sensors and i agree to that complete but any idea how i can only have light pass though an 8 x 8 inch square without worrying about hitting the lights themselves?

My intention is to have the arduino mounted nicely above and as I tare though wire meshes i can replace them