Why will my led not light up & why does my input voltage fluctuate when I add a wire?

Question

This design is suppose to light up the LED When the sensor is under light, and turn off the LED when the sensor is covered.

I noticed two problems:

1. My LED won't light up.

2. When I measure the voltage input difference (expecting +15- V) without the wire connecting the second prong of my 50k potentiometer (25th node) to the second prong of the op-amp, I measure 15 volts. But when I insert that wire how it is in the picture, my same input voltage measurement starts fluctuating. I assume this is a problem

Of course, I tried changing the values of the potent. and sensor but had no luck. I also tested my op-amp and it seems to be working correctly. The LED is also working correctly because it lit up in a different scenario. & Yes, I am also aware there is no voltage input in the photo. These were taken after I unplugged The input.

Will you please look over my design and help me locate the problem?

EDIT: New circuit based off new understanding

EDIT2: Just talked to my instructor. I indeed originally wired the purple wire wrong, but it should be fixed in the last two photos. I also confirmed that my resistor is not shorted and the photo is just confusing everyone, so I will upload a new one once I get home.

EDIT3: Less confusing photo (made sure you could tell the led is not shorted)

SOLUTION: Thank you @jonk and @TonyStewart!

My circuit was wrong in that I did not realize my potentiometer should not connect to the op-amp's 3pin (basically I didn't understand the schematic).

Later on, @jonk helped me come to the realization that there was something wrong with my op-amp, so I used a new one and it now works.

Answer 1

I think you may have wired it up wrong. It looks to me like you did this:

^{simulate this circuit – Schematic created using CircuitLab}

I think you want this:

^{simulate this circuit}

Pull the end of the purple jumper off of pin 3 and move it to your \$+15\:\textrm{V}\$ rail.

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Below is a piece of your schematic and some information I've added. The arrow points to a "cross-over" and NOT to a connection. Just in case that helps.

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Your newly added picture does appear to show a shorted LED. However, your first picture does not appear to show a shorted LED. I wouldn't have been able to tell from when I was reading your post, because your last picture wasn't added by then. Now, looking at it it does appear that it could be shorted out. Did you move it between pictures???

Anyway, that is another detail to look at and double-check. I think you already know (knew) that all five holes along a row are all connected together. That's a detail that everyone needs to know just to use a protoboard. So I assume you are aware of that. But anyone can accidentally get a lead in the wrong hole, too. So it's worth checking out just to make sure.

Best wishes here.

Answer 2

@jonk was correct in identifying the purple wire was wrong.

@WhatRoughBeast was also correct , your LED is shorted out and R is connected wrong to LED. FIX IT You must use a a voltmeter to debug your connections and learn to say "pin one" and write as p1 or U1-1 or pin1.

Compare my expectations below and record your results.

Pin    Function  Voltage
---    -------  --------
1     (out)   15V  V+ with LED off     0V with LED on     
2      (-)     0 to 15V pot V . Set to middle pin3 range 
3      (+)     0V in dark  3V in bright light
4       V+      Supply voltage

11      V-      Supply return or ground ( 0V reference )

The LED must never see reversed voltages or inserted backwards as -15V will damage LED. (-5V max) The Series R limits the current from the output switched from 0 to V+ and the voltage across RED LEDs rises to 2V when lit.

The pin 2 & 3 connections are reversed on schematic to match your description. Ambient light +V in makes output + and LED goes off when connected to LED -ve (cathode)

As is Pin 2 (-) is your reference level input from pot and if room is lit, Pin 3 (+) rises and if more than (-) then output goes high. ( We think by saying if + is greater than - then output is +true (high))