# Measure Resistance from Hand to Hand

Hi, I’m working on a project where I need to measure the continuity from the left hand to the right hand and have an multicolor LED that reflects the connection strength. Each hand will be holding a copper tube and I need to have some sort of visual indication of how well the connection is from one hand to the next holding on to the tubes. I would like to have a multicolor LED that will change from say yellow and glow brighter red depending on how we’ll the copper tubes are conducting from one hand to the other. I need this in order to make sure the make that someone is properly holding the copper tubes. Does anyone have a circuit design that would do this via the Arduino board?

Tnx,
R.

The resistance measurement might seem simple on the face of it, but RFI is an issue. Your body acts like a big antenna for AC 50/60Hz hum, and to all that hash from fluorescent lights, and from any nearby computers.

The old stuff relied on the isolation of a battery powered unit, and the inertia of an analog meter to smooth out any noise pickup.

So you can do some of this in software:

Does anyone have a circuit design that would do this via the Arduino board?

Since you are building something unique, I don't think anyone has the plans already.

What do you know and what do you need to know?

Do you have a multimeter and do you know what the range of resistances will be?

Are you familiar with Ohms' Law? You'll either need to supply a known current and measure the voltage, or supply a known-voltage and measure the current. The Arduino can't directly measure current, but you can measure the voltage across a series resistance of known-value and calculate it. I don't know which way a normal DMM works...

Do you understand how the Arduino's Analog-To-Digital Converter works?

I just did a couple of quickie experiments... I just checked the resistance between my fingers on one hand to the other with standard probes and I got a little more than 10M when I touch the probe-points and around 2M when I squeeze the probes with my fingers. I don't have any copper pipe handy.

Here at work I have two multimeters, so I set one to voltage and one to resistance. Open-circuit the Ohmmeter is putting out about half a volt. With a 1K resistor, the voltage drops to the millivolt range. But, it's an auto-ranging meter so I don't know if it's putting out a constant-voltage or constant-current. I gotta' get back to work, but maybe I can do a better experiment later to get a clue of how my DMM is working...

P.S.
I found a couple of references on the Net that say DMMs use a constant current source. That makes sense to me, and that's how I would have done it, simply because it's "easier" to measure voltage than it is to measure current. You'd have to build a constant-current source (probably with an op-amp).

You can get down to below 1k, depending on the person and a few other factors like humidity and sweat.

You can measure a wider range of resistance if you use a resistor than if you use a current source.

I'd go buy a chrome plated sink pipe and use that. Copper will corrode -very- quickly with handling and the resistance will go up.

Hi, I'm working on a project where I need to measure the continuity from the left hand to the right hand

Well, get a good multimeter and measure the resistance from hand to hand. Then you can see what you are dealing with.

And test it on many people.

Dry Skin is actually a very good insulator and its difficult to get repeatable results.
This is the reason that ecg machines use a gel on the contact pads

Thanks for the information guys. Yes, I have all the test equipment I need since I’m a extra class Amateur Radio operator and software Engineer =) I was just looking for a simple circuit that I could design some code around that would save me some time in reinventing the wheel =) I’m building a Freq Zapper similar to this http://huldaclarkparazapper.com/cgi-bin/cart.cgi/MY.html but using an arduino nano and a DDS-AD9850 freq generator brd. I already have the code working and pumping out the Freq sequences I need in the various modes, it actually works quite nicely and it’s only \$15 vs. \$380. I’m just trying to simulate a circuit similar to what the URL above is doing to measure when the hand connection is good. Their circuit changes an LED from yellow to red to indicate a good hand connection which is probably around 1-2Meg Ohm. I’m thinking on just using the attached circuit with with a BC547 transistor. What do you think?

btw, I’m sure there’s a lot skeptics out there to whether this is a worth while project to pursue, but I have to say until you try it, yes these frequencies are very affective in keeping a body healthy and detoxed. I spend a lot of time Mountain biking, Running, Martial Arts and eating right. But any little extra to keep the body detoxed is important. Thanks to the power of these little arduino microprocessors and add on boards you can create anything you want for a cheap price. I’m just about done with the project and the code, but just wanted to add the hand continuity visual LED support =)