I have a project in mind that I'm not sure is possible and would love some insight from those more experienced. I've played with a drawdio and love how you can complete a circuit through a person or multiple people. That got me thinking that it would be very cool to do the same thing with multiple objects. Like if there are 5 objects in a room and you touched two of them it would complete a circuit and make something happen. Then if two other objects were touched something else would happen. It would also be great to know if three objects are connected or more. Is this possible with an arduino? I'm positive I could make two objects work, but multiple? I would need the arduino to know how many objects are connected and which ones are in the loop. This is different from just knowing if an object is touched. I can do that easily with the capsense library. I want to know what objects are connected through a person or multiple people bridging between them.
I don't see why not. Skin resistance can be about 1 to 10K normally so it is easy to detect when a circuit is made.
However I don't see how you will physically connect three objects given that you only have two hands.
The idea would be multiple people connecting objects and holding each other's hands. I hacked a drawdio into a coat once so it played music when you touched different parts of a sleave and was able to complete the drawdio circuit while 15 people held hands in a big circle. That's what gave me the idea for something a bit more ambitious.
Some things to think about:
- Power source and voltage ? (probably should be current limited somehow to an appropriate level) . I don't see an issue using a 9V smoke alarm battery without current limiting.
- You need to do some empirical testing using a 9V battery an a good voltmeter to see what voltages you get with 1 - 6 people.
- You would need a comparator circuit or possibly even an op amp amplifier or both. With the comparator you probably would be seeing low voltages. With the amplifier you could adjust the gain with a high value (100k or greater ) potentiometer as the feedback resistor.
- No two people have the same skin resistance.
The idea would be multiple people connecting objects and holding each other's hands.
Yes but that does not explain the topology of three objects being connected. Remember each object will contain a wire back to the arduino.
Yes but that does not explain the topology of three objects being connected. Remember each object will contain a wire back to the arduino.
You could use small guage magnet wire that would be hard to see.
need a frame of reference for the human.
a female has a different resistance than a male.
are you talking left finger to right finger ?
or from a wrist cuff to the index finger ?
That's a good point that men and women have different resistance. The connection would be from hand then through multiple people to hand. I guess the idea would be to be able to know what objects are in the loop. Another hard part would be that it would have to be any two or more objects. With the drawdio you had the positive and negative side. With this idea it would have to be any objects. Would I need a single object to be the central one that is always part of the loop or could there be a way that it can be any?
Tall order I know.
The drawdio uses a AA battery and I was able to complete the circuit with 15 people. I agree that a 9v power source with a low current would be better. As a reference I just measured how much power travels through my body. Using a AA batery (1.5v) I got 0.65v going from my right hand index finger through my left hand index finger. The power doesn't drop that much when adding more people. You get most of the drop when you go from copper to skin, but the voltage stays up there pretty well from person to person.
As another reference, the longest human circuit lit up an LED through 1,113 people all holding hands in a big circle. Pretty cool.
a female has a different resistance than a male.
Ever measured that? It is wrong. It all has to do with skin resistance, nothing to do with bulk resistance. There is no gender difference. Skin resistance depends more on the wetness / clamminess of the skin.
That's interesting. I guess I need to test to see how much difference there is from person to person and work within that threshold.
You get most of the drop when you go from copper to skin, but the voltage stays up there pretty well from person to person.
Without seeing the schematic it sounds like a Mega-Ohm-meter circuit with a threshold comparator.
The power doesn't drop that much when adding more people. You get most of the drop when you go from copper to skin, but the voltage stays up there pretty well from person to person.
Worrying that statement, sorry but it implies that you have little grasp on electronics.
Power is voltage times current, it is not something that is "dropped"
Grumpy_Mike:
Worrying that statement, sorry but it implies that you have little grasp on electronics.
Power is voltage times current, it is not something that is "dropped"
Sorry, poor use of lingo. I meant voltage dropping when you go from copper to skin since skin doesn't have the conductivity of copper. I'm by no means an expert, but I know a little. We all have to start somewhere, right? My background is in video and lighting design for live performance. I know the basics of power, electricity, etc, and have done some really simple electronic projects mostly involving playing with 555 timer chips. Right now I think this project is over my head, but It isn't an immediate thing so I have time to teach myself.
I do have one idea that could work, but I don't think it is ideal. If I have one object be the common and each other object have there own power wired in parallel to the other objects then you would get an increase in voltage at the arduino whenever another object is added to the circuit since the current would increase. This doesn't solve the problem of using any two objects since the common object would always have to be in the loop. Forgive me if that doesn't make sense. I tested with AA batteries and it worked. One connection on my left hand and three batteries wired in parallel along the negative side. When I touch 1 battery with my right hand I get 0.5v (I guess my galvanic skin response dropped a little since my last test). When I touch two batteries I get 0.7v. When I touch 3 I get 1v. Using more voltage with a bit more current may yield results that are more usable since the difference between 1 and 3 batteries is so close that individuals skin conductance would most likely muddy up the difference between 1, 2, and 3 objects. This also wouldn't tell me what objects are in the loop, just how many.
raschemmel:
Without seeing the schematic it sounds like a Mega-Ohm-meter circuit with a threshold comparator.
I didn't even think of measuring ohms instead of voltage. That's interesting.
Grumpy_Mike:
I don't see why not. Skin resistance can be about 1 to 10K normally so it is easy to detect when a circuit is made.
Is your skin between 1 and 10K ohms Mike? If I had a skin resistance that low, I sure wouldn't be handling even a 12V battery!
Just for the heck of it, I tested my skin resistance with a digital multimeter, and no matter how hard I squeeze the probe tips, both across two hands, or with them side by side, squeezed between my thumb and forefinger, I get NO reading at all on the 200K ohm range. I do get a reading of betweem 4 and 8 MegOhms (lightly holding to squeezing tigthly, one probe in each hand), which is pretty much what my skin resistance has been ever since I got into electronics over 50 years ago.
Perhaps you meant 1 to 10 MegOhms?
No I can get down to 1K, as measured by my trusty Avo Minor Mark 6 analogue meter with one AA cell in it. That was when I was a kid, I haven't measured it lately.
Did you know a mega hurts is a schock from an insulation tester abreviated MHz
retrolefty:
Anyone ever use a hand crank megger? The sparkies at the refinery used them to test motor winding insulation. You could light up a large number of people with one of them.
I once loaned my telephone magneto to the school for demonstration purposes.
I received a call to come and collect my daughter after they had done the experiment of having the class all join hands and the end students held a terminal of the magneto. Shortly subsequent to this my daughter had fainted and hit her forehead on the edge of the science room bench. I had to collect her and suture the laceration with all due care and some 6/0 nylon.
The school duly returned the magneto with thanks for the loan, but did not expect to require it in future.