Research Journal


Wednesday May 1st, 2013

We tested the device today and saw the LED light flashing in sync with the heartbeat, felt on the wrists. Below are the traces taken from the osciloscope.

We tested Dr. Noe first and as expected, his pulse was detected instantly

Then my pulse was also observed on the scope. It was quite difficult to get this picture since I had to be very still and careful not to even slightly move my finger from the sensor


Wednesday April 24th, 2013

URECA Poster presentation

Dr. Noe explained why it is not ideal to use the output of a voltage divider as a power supply



i2=i1+ V/R

(15-V)/2R=i1 + V/R

15-3V = i12R

-3V=2Ri1 - 15

3V=15-2Ri1

V=5-(2/3)Ri1

We designed the circuit such that it would deliver 5V output voltage. We see here that if the output impedance is not low enought, the ouput will be less than 5V


Wednesday April 18th, 2013

I borrowed the protoboard from Dr. Noe to in order to possiby work on building the signal conditioning circuit this weekend.

I also dereived the gain for our amplifier. We see that Rf and R form a potential divider network

V1=Vout R/(Rf + R)

Using golden rule since we're having negative feedback

V1 = V-

V- = V+. Thus V1=Vin

Vin=Vout R/(Rf + R)

Vout/Vin = (Rf + R)/R = 1+ Rf/R

From our values, the gain for each stage is G=1+680/6.8 = 101

The circuit is now completely built but it doesn't seem to work at all.

The problem found was that the photodiode was forward biased.


Sunday April 14th,2013

Active band-pass filter Active band pass filter has an ability to pass frequencies over a specific band of chosen frequencies. Active band pass filter has an amplification stage.

During the 1st stage of the active band pass filter, the high-pass filter stage uses capacitor to block any DC current biasing from source. This is important in this project because only the AC component of the PPG signal is desired for our heart rate measurement.

Saturday April 13th, 2013

Single supply op-amp

When working with a unipolar (0-Vcc) as opposed to bipolar +/-Vcc supply, certain design consideration must be made: can't generate negative input

Rail-to-rail op-amp This is commonly used when designing single supply. They can deliver output voltage very near the power supply or rails. The opamp MCP6004 is the one that we're using for this project with unipolar supply.

Virtual ground It can now be used just like a normal ground in your circuit It has limited output current. Therefore, it is advisable to use the op-amp in its inverting configuration since this doesn't require current output.


Wednesday April 10th, 2013

n order to prevent the sensor detecting room light, I used black tape and foam to surround it. We connect a resistor across the photodiode to convert current into voltage and a coaxial cable to feed the input into the commercial amplifier with frequency range of 0.3 to 10Hz and adjustable gain.

Thursday, March 28th, 2013

We started off by making a sensor including of an IR LED (peak emission at 850nm) and a photodiode (peak sensitivity wavelength at 900nm). We used a removable photodetector to detect transmitted signal from our fingertip. Signals from some individuals were not well detected. Only Dr. Noe's signal could be clearly seen on the scope screen. We were sure it was his pulse because we felt it being in sync with the signal viewed on the scope screen

For the IR LED, we used a limiting resistor of 100 ohms to prevent large current passing through it.


Thursday, March 20th, 2013

Dr. Noe discussed a possible project that ralates operational amplifier. It regards the heart rate monitor circuit. A brief explaination of the project can be found in this website $Heart Rate Measurement from Fingertip$

The main point of the project is using active band pass filter for PPG signal conditioning. And since I'm taking an electronic course, this would be a nice complement to the course


Wednesday, March 6th, 2013

During my meeting today with Dr.Noe, we talked about a few basic linux, and html commands. I explored and found a few videos that cover these basic commands with screen demonstrations. Click here for a sequence of these Command Line Basics tutorial. There is also a website especially for HTML tutorial with "Try it yourself function" in every small topic you want to learn.

I also explore to put picture in my journals or webpage. It's difficult to imagine of what to do at first; therefore, I'm going to use these commands in my specific examples, which you can relate to your own cases. First, I quit my laser account. And go to where my picture is located. In my case, it is one of my folders on my camputer. Then I type scp foo.jpg foo@laser.physics.sunysb.edu:public_html

foo.jpg is the name of the picture, foo is my username, laser.physics.sunysb.edu is the host name, and public_html is my destination path. You can leave it blank after the colon. If so, your picture will be uploaded to your top directory. Or you can put any directory of your choice. Hit enter and your picture will be instantly uploaded.

Now that it is uploaded, I will log in my laser's user and go to my journal dicrectory using "cd" command. Then I open my journal using text editor command "pico", I typed < img src="foo.html" > without the spaces between the brackets. THen save the text editor and refresh the page to see the image posted on my page.

For changing your profile picture, you can go back to your public_html directory using command "cd .." (this is for my case because public_html directory is just above my journal directory). In order to edit this page, we use the command "vim" without the quotation marks. Once this is open, it can not be edited unless I is pressed. You can remember I as insert. To save and quit, we use ":wq". Hope this will help! Happy exploring!


Wednesday, February 27th, 2013

During my meeting today with Dr. Noe, we talked about a few SSH basics so that I can get access to editing, adding my journals, or project ideas on my webpage. Also, Yuning, a new graduate student, discussed and demonstrated coupling light into optical fibers. It wasn't easy at all. The physics behind this (for a relatively large fiber; otherwise, we need electromagnetic theory) is total internal reflection. We want our light to be totally reflected and traveling inside the fiber. For this procedure, we need to consider the positions of lenses as well as their focal length since the waist 2wo is affected by these factors. The smaller the waist 2wo is, the harder it is to place the fiber. We also don't want a big waist 2wo; we want the ideal figure. When walking the beam, the tilted intensity contour should be considered. Dr. Noe uses the term "walking" because as we adjust one mirror, we also need to compensate by adjusting the other. And both should be horizontally or vertically adjusted. Hopefully, tomorrow I will be able to get the mirrors in position to see some pretty "wormie" pattern or lucky enough to see an Airy pattern through a single mode fiber!


Thursday, Feb 21st, 2013

During our meeting today, we talked about optical aberation. Optical aberration is the distortion in the image by an optical system compared to the original

Agtimagtism: distortion occurs in lenses because a lens has a different focal length for rays of different orientations (basically image in not focused)

Chromatic aberration: lens fails to focus all colors to the same convergence point because lenses have different refractive index for different wavelength of light. THere are two types of chromatic aberration. Axial(transverse) occurs when different wavelengths are focused on different points on the optical axis. Tranverse(lateral) occurs when different wavelengths are focused on different points on the focal plane

Coma: off axis rays not quite converge at focal plane

Spherical aberration: occurs in spherical lens or mirrors because they don't focus parallel rays on a point but along a line.

Field curvature: occurs because the focal plane is not planar but curvature

AR (anti-reflection) coating is a type of optical devices to reduce reflection so less light is lost.

Slow light: propagation of optical pulse at very low group velocity when a propagating pulse is substantially slowed down by the interaction with the medium


Thursday, February 28th, 2013

Today during the meeting with Dr. Noe, we talked about operational amplifier. What is operational amplifier? Operational amplifiers are high gain (105 or 106) DC-coupled amplifiers with single ended outputs. Below is the universal symbol for operational amplifiers. Here (+) stands for noninverting input and (-) stands for inverting input.

The amount of available operational amplifiers is overwhelming. You can find these in Table 4.1 of "The Art of Electronics" by Horowitz & Hill (pg.197-207)

Op=amps' Golden Rules

  1. The output will attempt and try to make the voltage difference between the inputs zero.
  2. There's is infinite input impedance. Thus, there's no current flowing through them.

Let's try using these rule to analyze some basic op-amp circuits

A) Inverting amplifier Rule 1 says that A is also at ground and that the voltage across R1 is Vin and the voltage across R2 is Vout. Because there's also no current flowing through, Vout/R2in/R1 (Ohms' law) or Vout/Vin = R2/R1 V_out/V_in is called the gain.

B)Non-inverting amplifier From rule 1)VA=Vin. We see in this circuit that A is connected to the output of a voltage divider. If we remember Thevenin's equivalent circuit, then Va=Vout(R1)/(R1 + R2)for this particular circuit. And since we have Va = Vin, the gain is Vout/Vin = 1 + R2/R1

C)Voltage follower Rule 2 says that Zin is infinite and this impedance isolate the output from signal source. Thus, very little power is drawn from the signal source to avoid loading effect.And Vout = Vin. Therefore, the gain is 1. If we compare this with the non-inverting amplifier above, it is simply the non-inverting amplifier with R1 = ∞ and R2 =0.