Hello, I'm a computer science student and I was assigned by my professor to make a monostable multivibrator circuit on a bread board with an unstable duration of three seconds. Keep in mind I have very little knowledge about circuitry, we were only given the schematic and were told to find the values for the components ourselves. After watching a YouTube video I got some of the values myself and ran the circuit on a simulator and the stable state worked fine, however when I applied a trigger pulse through the differentiator circuit the output (in this case tracked by a LED) turned on for less than a second then turned off. I can't determine the cause for this and as to why the light won't stay on for three seconds, I did the math for the time constant which is T = 0.693RC, at this point I'm thinking the differentiator circuit values are to blame.
view attached (source supply is 9V)
view attached (source supply is 9V)