Objective: To build an astable multivibrator circuit using passive elements and an operational amplifier.
Application/use: From this project, I hope to build a reliable and accurate square-wave generator.
Why: Since I am interested in analog electronics, I figured it would be worth-while to build my own waveform generator. I've been anxious to build an astable multi-vibrator since hearing about them in my electronics class. Thus, I thought this project would be a decent start.
Simulation
I enjoy using the Falstad online simulator for simulation. It's fun to use, and the visual aids provide an idea of what's happening in the circuit. I wouldn't build the cure for cancer on it, but it's an exciting and effective tool for students and hobbyists!
Here is a link to the simulation for this project:
Waveworks Lab: Astable Multivibrator
With the power of imagination, pretend the 100ohm resistor at the output of the simulated circuit is a speaker.
Feel free to play around with the circuit and the Falstad simulator!
Build
You may observe the remains of a voltage divider at the bottom of the breadboard. Those resistors are just sittin' happy and have nothing to do with the multivibrator for now. :)
As you can see, the physical build of the circuit is fairly simple. With not too much of a "rat's nest" wiring going on, you actually may be able to trace out the circuit from this shot alone (with the issue of picture quality completely ignored). Indeed, I attempted to keep the color coordination of the positive (red) and negative (blue) railing. Both horizontal strips at the very top of the breadboard are part of the common node.
The oscilloscope probe shown reads the voltage across the output of the Op-Amp and the common node.
Results
...*Drumroll*...
The Reaction
I would say the results are pretty okay-ish kinda alright. Certainly not spot-on, but when I take my contact lenses out, it's really not that bad! From two cheap 9V batteries and a few more less-than-perfect components, I'm pretty happy with the results!
The Rundown
The mean is fairly low (200[mV])which is desirable. A perfect and ideal system would have a mean of zero. Therefore, the closer the mean is to zero, the better!
I am also pleased to see how linear those peaks are! Clearly, they are not completely flat, yet it's significantly better than what I was expecting.
By far, the result closest to the simulation is the frequency of the wave. I am not sure why there are two values on the oscilloscope screen (suggestions?), but both are very very close to the frequency acquired in the simulation.
The Verdict
80% pleased=mostly pleased!
I plan to look for areas to improve on this project. Especially after hooking up a computer speaker (hp 390905-001) in series with a 100ohm resistor to the output...
So this changes things a little bit, but it's definitely something I will be looking into. Any ideas on what's happening with the huge reduction in the Vpp? I have my own ideas, but I'll save them for now.
End
WOW! If you actually read all of that, then I deem you a Grade A++ nerd! (wear that title proudly) If you didn't, I don't blame you. Yet, I hope you learned something on the few parts you found mildly interesting!
Perhaps you know some material I need to learn! Maybe you seriously think I should review Kirchoff's Laws when I complain about blowing a fuse after wiring the positive and negative terminals on my power supply box! As described in my blog's description, I'm still a noob at this stuff. However, I am a noob eager to learn new things. I especially appreciate expert advice.
Please feel free to leave questions, comments, supplemental materials, suggestions (I'm new to this whole blogging thing), poems, McDonald's job openings (if you deem appropriate), IBM job openings (if you deem appropriate), and anything you feel like sharing!
Really though! If you have any suggestions on how I can improve the quality of my blog, you will be a saint in my mind!
...I need a catch phrase...
"Stay positive!" -Kaylon (Yeah, I'll work on that...)
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