Week 9/10

We will calculate the resistance values from the voltage values we received using the resistance measured on the orings. We will also integrate a LED light and threshold value into arduino to simulate the alert to a dehydrated individual.

Our results met our expectations. Unfortunately  we were not able to integrate pulse oximetry.  Many modifications from our original proposal. We did not use matlab or a DAQ, but instead used arduino and LabView. The orginal circuits we designed had to be modified completely.

The red line represents tests done with moisture and salt on the fingers emulating sweat, the green line represents only salt on the fingers and the blue line is a dry test, emulating normal hydration.

In future work, I would expect to design a microcircuit, with small orings that could be applied to the skin, with internal power supply. I would try to collaborate in research with MC10 in their development of a flexible band-aid like waterproof circuit to monitor hydration levels.

Week 7/8

We had to resort back to the wheatstone bridge complicated design with three opamps, rather than the simple wheatstone bridge. This was because the bridge experienced a backflow of voltage without the two buffer opamps present. We added an exra resistor and a pot (potentiometer) to offset the voltage to zero.

We tried outputting the voltage using the arduino to matlab to no avail, so we upgraded to Labview. We had to install the drivers for arduino and the arduino package for labview. We learned how to create a pictoral code to measure the input voltage from arduino, create an array of numbers, graph the data in an xy plot of voltage over time, transpose the data into excel,  change the time intervals and baut rate, and use a boolean clear data function.

The voltage over time was collected in numerous trials. Trials included 2 different days, different testers, with salt, without salt, with water, without water and with salt and water. This was to emulate the change of resistance on the skin due to sweat. Sweat contains a high concentration of NaCl, which conducts electricity. We found that the addition of water and salt creates a higher measured voltage. The normal voltages range from 0 to .35 Volts. With the addition of salt and water, the voltage reaches over 2 Volts. The resistance was measured across the Orings as .99 MOHMs, so that we can calculate the conductivity.

With the testing and building of the circuit, as well as coding and output now completed, our group is to focus on analyzing the data, and creating trends and graphs.

The graphing and volt meter in Labview measuring the voltage across two fingers with the addition of salt.

The accompanying Labview code to interpret data from Arduino

Wheatstone bridge. Modifications included adding a resistor after the third opamp to offset the voltage to zero, a voltage diver for the op amps supplying 7.5 and -7.5 volts, and 5 V directly given to the bridge.
Note: The two other designs of a less complicated wheatstone bridge, and the circuit seen in week 6 were ultimately failed designs.

Arduino UNO microcontroller. The device measures an input voltage value from the circuit and outputs the value to LabView.

Week 5/6

We have successfully acquired all the necessary materials, including a pulse ox and substitutes for both circuits. We built our finger resistors, which are made from wires, alligator clips, and o-rings.

We are building two different types of circuits, one including a wheat stone bridge, and then assessing which one is more accurate in readings.

In testing the wheat stone bridge, we came across a few obstacles. We connected the breadboard to an oscilloscope and 5V of power, but there was no signal received  First, our initial op-amp was defective, and we were able to spot this by testing each of the three op-amps with our finger to see if it was getting overheated. The first one was very hot, and therefore pulling too much current. We then replaced the TLC080 op amp with a new one.

The signal was still not received  so we tested each individual piece of the circuit with a voltmeter to see where the problem existed. We found that current into the op-amp was not getting buffered as it should, but gaining over 4 volts. We also found that the op-amp was drawing a large amount of current. We switched the op-amps to two sided LM741 op amps. The problem still continued.

The voltage was then changed from .5 Volts to -.5 Volts, and some signal could be read. However, the voltage output from the circuit was much too small (measured in mV), so something else was wrong. We postulated that it could be due to the resistor values in the circuit, and that the voltage drop over the finger resistors was too large. We then decided to change the resistor values, multiplying by a factor of ten. Our new resistors were 20kOhms and 390kOhms.

The new resistors were tested but the voltage output is still negligible and the signal in the oscilloscope was very noisy. We are still in the process of troubleshooting the circuit.

The signal was too noisy; therefore there is some error.

As stated before, the group has constructed two different circuits to test which one gives the best results in relation to our project. The second circuit's schematic is shown below:

The schematic for this circuit was found at the website http://produceconsumerobot.com/truth/ and was originally used to detect emotional response.  

Our completed circuit looks as follows: 

The circuit has some issues that we are troubleshooting currently. The LED does not turn on when there is a voltage supply, and in one instance, when the battery was connected the LED quickly flashed on and off. We will choose the circuit that produces the best results, or biggest change in voltage when skin conductivity is measured.