Looking to make a 2-contact Bioelectrical Impedance sensor...a body fat sensor with arduino. I have done a lot with arduino before, but its all fun and games till the project requires running current through your body. Im much more hesitant now, anyone have any experience outputting around the 0.05v that the scale-type units use?
Im not fonding a whole lot online about these measuring devises, and Im confused why there are 4 contacts on most, and not just 2.
any insight is greatly appreciated
Very interesting project! How would it be connected to the user (feet+hand, hand+hand, ...)? What algorithm had you intended to use for the calculation, once you've got your reading?
I'm no expert, but I would say that generally, the Arduino is not a small current, low voltage device. I would be bolder in voltage/current output to get more reliable readings. As long as it is not fatal, but only stinging/buzzing for an adult you should be fine. Just put a visible disclaimer on the device and make sure it does not look "professional" so that no one can claim they were fooled by the looks of it.
Algorithm will come later..if I get some set of readings. I know making a galvanic skin resistance sensor is super easy, but measuring impedance is whats beyond my thought now. I dont even know how to begin.
Im doing hand-to-hand.This isn't for a professional devise, so I'm not worried about any disclaimers, I just don't want to make that time machine from Napoleon Dynamite
Ok,
again, I am no expert, but I notice you use the term "impedance" instead of "resistance", so that to me would give a clue to the 4-connector, vs. 2-connector question you had.
2 terminals = resistance
4 terminals = impedance (real + imaginary part)
Impedance also suggests alternating current (AC) to me. Are you planning to tap your measurement reference signal directly from the grid? Although I agree it is probably accurate enough, it is not healthy to send that amount of voltage and current through your subjects. You need to drop it down to under 110V I guess, probably under 70V to be withstandable by the subjects.
I would also worry more about the algorithm. Once you have your reading, how do you tell fat content from muscle based on that?
You need to drop it down to under 110V I guess, probably under 70V to be withstandable by the subjects.
Pssht just go for straight 220AC. If it doesn't kill you it makes you stronger
Look at this
anders2009:
give a clue to the 4-connector, vs. 2-connector question you had.2 terminals = resistance
4 terminals = impedance (real + imaginary part)
Nice idea but wrong. From 4 terminals 2 are used to force a current through the resistor, and the other two are used to measure the voltage across the resistor. This trick will eliminate the voltage drop on the wires that feed the current to the resistor.
I really don't think the OP will read your comments. This thread was started 9 years ago. And those involved at that time are no longer members.
OGGIOGG:
Looking to make a 2-contact Bioelectrical Impedance sensor...a body fat sensor with arduino. I have done a lot with arduino before, but its all fun and games till the project requires running current through your body. Im much more hesitant now, anyone have any experience outputting around the 0.05v that the scale-type units use?Im not fonding a whole lot online about these measuring devises, and Im confused why there are 4 contacts on most, and not just 2.
any insight is greatly appreciated
What you call bioelectrical impedance MUST be something different from electrical impedance because electrical impedance is AC related. Both inductive and capacitive impedance have "2piF" in the calculation. F being frequency.
Paul
DrDiettrich:
This trick will eliminate the voltage drop on the wires that feed the current to the resistor.
Or in this case, feet! 
Don't waste your time on this one.
Just yet another case of a first poster resurrecting a 9yo necrothread for no good reason.