Alert when circuit made of conductive ink is broken

Projects General Guidance
1

Hi,

Im very new to the world of Arduino. I'm not an incredible developer but i do have some experience programming in Python and R so i have the basics down.

I have bought an arduino for a specific purpose to develop a prototype for an idea i have. My goal is to use conductive ink to make a very basic circuit on a piece of paper. When the paper is ripped and the circuit is broken i want the time and date recorded - for now thats it. The next step for me would be to get a bluetooth sensors and send that data to a mobile device.

I'm wondering if anyone can give any feedback on a sketch i could base this idea on? I genuinely have searched online although i believe i may not know the right terms to search yet: google brings back a lot of stuff for 'arduino circuit broken alert' but nothing that seems directly related to what i want to do.

I apologise in advance if this is a very basic question, i'm hoping to accelerate the project by reducing time wasted online (although i do know thats a big part of running a project). If it was simply a case of doing something virtually and i was coding this in python i do not think this is complex e.g.

if circuit intact
do nothing
else
record time/date

however because i'm completely new to arduino/electronics it's definitely a bit of a challenge.

Any feedback on the steps required for me to achieve the above would be much appreciated. I'm going to a meet up this week with some other adruino users so i'm hoping to get a bit of steer/feedback there too!

Thanks!

2

Given the circuit is a direct path from an IO pin to ground (all you need here), you can set the pin like so;

byte sensePin = 7; // could be most any pin

....

pinMode( sensePin, INPUT_PULLUP ); // this pin can be safely grounded

And that pin will source 5V through an internal resistance of 20K ohms to 50K ohms.

You read the pin

byte pinState;

....

pinState = digitalRead( sensePin );

If the pin is grounded, pinState will be 0, if not it will be 1 where 1 indicates a broken circuit.

Arduino Foundations Page -- one info source you should welcome.

3

Thank you, much appreciated. This is brilliant as it essentially means i dont have to get any more equipment or worry too much about development at first and can get a protoype running quickly to prove the concept!

Thanks!

4

May be as well to include a 1k or so resistor in series with the Arduino input to protect against ESD from physical contact with the paper. And a couple of diodes to Gnd and 5 V to support the internal ones.

5

When I needed to connect to aluminum foil (DIY cap sensing) I used paper clips soldered to jumpers.

Could you use anti-static bag or foam instead of paper? It resists at meg-ohms per inch but won't build or hold static when grounded.

6

Hmmm possibly - my concern here is i need to break the circuit easily and im not sure the static bag would be easy for an end user to tear (think of a child being able to rip the circuit easily!).

Foam could potentially work...or a think layer polystyrene (?). Can i ask what you mean by ESD? Im just wondering what other options there are now, key usability requirements is it can be broken easily by tearing with hands and its a think layer (hence me thinking paper could work). Im not sure if Cling film / similar could also be a possibility? What about cardboard?

Just to clarify on the circuit side of things the circuit you mention Pin 7 - so the circuit is basically 'leaving' pin 7 and 'entering' back into GND (apologies for my crude terminology) - i'm thinking the best way to do this is to use the jump leads to make a connection to the conductive ink on whatever medium i use to draw it on?

7

ESD is electro-static discharge. The paper could possibly pick up a small amount, the dryer the air and paper the more that could be.... why I mention grounding the trace first.

Back in the vinyl record days the records would get some charge and collect dust. Anti-static brushes with polonium in the bristles were (probably still are) used to neutralize that. Grounding yourself and wiping with a damp cloth worked too but not as convenient/elegant.

Talk with a physics teacher about the issue and maybe add the resistor and diode. I would try making an antistatic brush out of antistatic foam with a ground strap IF I thought it needed doing.

Take 2 sheets of paper, hold them insulated (not in bare fingers) and slide one over the other. Then bring them slowly close. If they have static, they will repel each other and not hang straight down.

If you make the paper strip even slightly conductive and ground it, it will not hold static. Even slightly dampened not enough to get into the paper would do. OR buy a can of air made for blowing dust off PC boards (should say anti-static on the label) if you're reasonably paranoid.

Heck, maybe there's a lesson for the kids to get them started, static electricity is a whole subject with some they-can-demonstrate-and-learn experiments that teach electric fundamentals.

8

rors100:
Just to clarify on the circuit side of things the circuit you mention Pin 7 - so the circuit is basically 'leaving' pin 7 and 'entering' back into GND (apologies for my crude terminology) - i'm thinking the best way to do this is to use the jump leads to make a connection to the conductive ink on whatever medium i use to draw it on?

Yah. Paper clips, alligator clips, just make good contacts. I'd use the paper strip.

You could also try using thin varnished wire used for winding small electromagnets. It breaks pretty easily.

If the strip is not wide, a slice of fresh fruit of veg might also do. Maybe even a french fry.