Photo sensor

[Tony Gunk]

Hi,
Basically I've been given a circuit and I need to find its limitations, propose improvements and of course give justifications. To be honest I've been stuck on it all day it would be great if someone could help me. Thank you for your time
The circuit:

 

[Audioguru]

Why does the opamp U1 have no part number?
The text on your schematic is very fuzzy and hard to read.

 

[AnalogKid]

What is the "analog output" used for?

ak

 

[(*steve*)]

I think @Tony Gunk should start by explaining, as best he can, how he thinks the circuit operates.

Even better if he can then come up with some limitations.

And then we could discuss improvements to address those limitations (or maybe decide that those limitations are things we can live with as long as we know what they are).

 

[Tony Gunk]

Here's how I would explain the circuit operation

· Amplifier: amplifies the difference in voltage entering the component.

· Digital output: Tells if something is above the sensor or not. The voltage varies between a high value, which means something is present, and vice-versa.

· Analogue output: Variates according to how close an object is.

· Diodes: Converts AC to DC, plus protects circuit from high voltage.

· Photodiode: The more light there is, the lower the resistance and vice-versa.

· Resistors: R1, R5 and R6 protects respectively LED1, LED2 and LED3 from high voltage. This way safe values are kept. R3 and R4 surround the potentiometer in order to reduce the risk of errors. The photodiode and R2 form a voltage divider which significantly reduce the voltage’s magnitude to make it useable.

· LED2 and LED3: Tell us if something is in the vicinity of the sensor or not. LED2 tells us that nothing is present and LED3 the opposite.

· LED1: Emits ultra-violet light that is reflected on objects in its vicinity and is received by the diode.

· Regulator chip: Stops the voltage from being too big and stabilizes it.

· Capacitors: Soothes the variation in voltage and act as a store of electric charges.

· Potentiometer: Is a sensitivity adjustment.


About the limitations and solutions I am not really sure how to start, as my electronics skills are quite limited. A limitation could be that the circuit is only efficient with small voltages, an other one that this type of sensor only works on short distances? At first glance I would say the photosensor could be improved if we replace the photodiode by a phototransistor. An other idea would be increasing/dercreasing the value of some resistors, maybe add/move ground connection and finally perhaps adding a inductor?
I apologise for being so vague.

 

[WHONOES]

The circuit looks fairly simple. What range is the detector required to work at.
As a first suggestion, look up "reflective photo interrupter".
I should imagine that U1 is a comparator of some sort.

 

[Kabelsalat]

Bad quality of uploaded image - need improvement.

If you have an actual build of the circuit in your class room, assuming it does work - being able to describe the process and environoment where the circuit is used is the first thing you must do before anyone exept your teacher can provide any suggestion.

Also, as mentioned before - are you assuming ideal comparator, or do you actually have a name for the opamp?

 

[Tony Gunk]

Hello,
Would it be possible to delete this thread as I have already submitted my work and I have stupidly shared information that is exactly as it is in my work. I would like to avoid being accused of plagiarism of my own work.
(*steve*) ?
Thank you

 

[Kabelsalat]

Deleting threads is generally a very bad idea because of many search engines may point to this thread and other people out there may learn something. If deleted you bet it takes a very long time for search engines to update, leading people to having a negative perspective of the forum itself (broken links, you know).

A better ida is to put a watermark on your image prior to uploading. That way it is very difficult stealing your image just like that - because your name is all over the place...

If this is for school, there is still a great chance that if somebody (pretty unlikely, but still possible) that isn't serious about learning about electronics just get to draw a copy themselc by looking at your drawing.
In that case, I would try to place some component on odd places, but not too obvious. Draw some components backwards e.g.
If somebody just draw off your schematic (they actually spend time on this because you have a watermark on your original drawing) they will also draw the oddly placed components - where it is very unlikely someone would draw it excactly the same way as you - and therefore you'll know that they have copied your work.

Shortly put - even if your schematic makes no sense for anyone out there that haven't got the very same school assignment, I'm very against deleting threads. I'll guess other folks around will agree.