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.
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:
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.
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