Redesign/Update of dated systems (Student Project)

Thread Starter

LittleCamel

Joined Nov 27, 2019
3
Hello all!

For the last project for my application of ICs class, we have been tasked with updating Northrop and Nilakhe's No-Touch Ocular Pulse Measurement System. I attached the assignment specifications that I was given as well as the article itself that is mentioned.

I've read a lot of questions and answers on this site before, but I have never myself posted anything here. I'm trying to put up this project because I am very lost on it and am searching for any guidance I can get.

For this project, we are to redesign/update the systems shown in Figures 1, 8 and 9 in the article, though they are expected to be dramatically simplified for this undergraduate IC class. For example, we will not be using any kind of sensors to measure eye movement, but instead will be using a function generator as the input. We are not intended to design every portion of this circuit to have it operate exactly as it would in the systems outlined in the report, but instead we are to replicate the "concept" of each circuit.

For example, for Figure 1, my thought thus far was to create a PLL that could lock on to extremely low frequencies , like those of a human heart beat (so essentially 60 beats/min, or 1 Hz). I discussed this with my professor and he agreed that this would be a solution to the problem, though it would be impossible to design a PLL to operate with such low frequencies, which I agreed with. He recommended I build a frequency multiplier to up the frequency for the PLL, then divide it down afterward. For the PLL portion, we have built these before in the class using an LM565, but after looking into frequency multipliers I was having trouble finding something that was simple enough for this course while also accomplishing what I needed for such a low frequency signal. Figure 9 requires that this same circuit that "locks on" to the eye's movement be able to reset itself if the signal is lost (i.e. the subject blinks). This is one portion that I am very stuck on as I don't have a good idea of something I could build to do this. I've looked at the possibility of using a LM555 as a SR flip-flop to reset the PLL circuit, but in practice I really don't know how to do this.

As may be clear by now, we are only meant to redesign these systems to mimic the general concept of the original design rather than create some kind of eye tracking device. I don't have access to a significant number of components, but we have used simple ones like LM565s, 555s, 380s, 386s, 741s... etc. as well as typical resistor and capacitors (we haven't worked with many inductors so I'm not sure if we have much ot anything for that). This post is already really long, so if you're still reading, thanks for sticking with me. I'm not looking for an answer, or someone to give me a full design; all I wanted is to see if anyone can give me any kind of guidance on what I should try because I feel very lost. We are expected to complete this project in a week while most students like myself are home for the Thanksgiving holiday and are completely unable to test possible designs. I'm terrified I won't be able to come up with any kind of product in the time we were given...

Thank you for your time, and if you celebrate the holiday, then Happy Thanksgiving!

Also please tell me if more information is needed or if I've posted this in entirely the wrong place.
 

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BobaMosfet

Joined Jul 1, 2009
1,117
I'm not sure what your problem is, the PDF explains it well. You stated you were wondering how to deal with blink. Page 3, if you read the paper and comprehend it, tells you exactly what to do:

"The NOTOPM system also includes a circuit to permit precise
adjustment of the mean cornea-to-transducer distance (x) to
within one ultrasound wavelength (see Fig. 8). Another circuit
is used to compensate for blinks automatically; it opens the
PTL when the received signal is lost for over two cycles, and
closes it after it has been restored continuously for 100 ms
(see Fig. 9)."


The most important aspect of being an electronics designer, not just an engineer, is the ability to recognize the problem's actual limits, and find a solution to meet them.
 

Thread Starter

LittleCamel

Joined Nov 27, 2019
3
I read through the article and discovered the general purpose of each of the systems shown, I guess my problem is the execution of this. For example, I am unsure how to design a circuit that when triggered can short the integrator capacitor of the circuit in Figure 1 that will allow for the VCO to be reset because I haven't designed or built something that can accomplish this before. I tried to look at this myself, but have had trouble finding something that I understand or is reasonable to be built within our provided lab. Perhaps I'm not remembering correctly, but I've found that the PLLs I've built using a LM565 tend to stay locked on to a signal even if the input is turned off and back on (this being synonymous with the blink). I'll just continue looking for possible solutions to this.

Thank you for your advice!
 

BobaMosfet

Joined Jul 1, 2009
1,117
You're not reading for comprehension. Page 9:

"This falling edge triggers a
control flip-flop to open the loop and short out the integrator
capacitor with MOS switches (not shown)."


1575038541139.png

Do you understand what a 'short' is? I think not. A short is when you ground something without any impedance in the middle of the path.
 

Thread Starter

LittleCamel

Joined Nov 27, 2019
3
Jeez, man. I'm sorry that I'm confused on this project. I have never built the majority of these types of circuits before. No need to be rude with your replies, I'd rather just get no answer at all.
 
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