Build a Square Wave Oscillator - Part 1 of DIY Modular Synths

Picture of Build a Square Wave Oscillator - Part 1 of DIY Modular Synths
Synthesizers have become an incredibly prominent instrument in modern music; it's difficult to hear a track without one anymore! Unfortunately, many synthesizers are incredibly expensive and hard to acquire, making it rather difficult for the hobbyist or budget musician to get any of those sounds. This instructable won't teach you how to build one of those feature-rich, user friendly synths, but it will start you off with a very simple device that can be used with other units to create interesting and unique sounds.

The following is the simplest and most fundamental piece of a synthesizer - an oscillator. This particular oscillator is a "Square Wave" oscillator, and has limited functions, but can still be used every now and then for fun sounds.

Let's get started!
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Step 1: Gather Your Parts

Picture of Gather Your Parts
The square wave oscillator is a rather simple device, so not much is needed to construct it. Most of these parts have some sort of alternative that can be found at radioshack, but I prefer this website for all of my electronics projects:

If you can't find all of these on that website, I would also suggest digikey.

Here's a list of everything you'll need:

-Project Enclosure
-2x 500kΩ Potentiometers
-Radioshack Perfboard
   -1x 4.7kΩ
   -5x 1kΩ
   -2x 1MΩ
   -1x 100µF
   -1x .001µF
-LED, any color
-741 Op Amp
-1/4" Audio Jack
-9v Power Adapter Jack

You will also need a few tools:
-Drill Press
-Drill Bits of Varying Sizes
-Drill Bit Index
-Safety Goggles
-Soldering Iron
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teeveebee1 year ago
Could somebody try to remove the 1MΩ resistor that connects to the audio jack? I don't have it and mine makes no sound at all, but I'm not sure if that's the only problem.
dnhushak (author)  teeveebee1 month ago

That resistor is just a pulldown resistor to prevent pops and clicks if there's a line selector or hard relay switch somewhere down the line, it shouldn't affect the audio output at all. I realize you left this almost a year ago, but I hope you've got it figured out!

I got mine working without the volume potentiometer. Simulations didn't work with it connected to ground. Didn't try it irl though. I will try when at home as soon as I have time.

I have headphones with one broken earplug. I use them for these kind of projects with mono sound. No problem if I break the other half. You can also use cheap headphones for testing.

paren0631 month ago

so what is the frequency range for this oscillator? What are the components that regulate this range? Thanks!

dnhushak (author)  paren0631 month ago

Using the schematics shown, you get roughly 207 to 310 hertz. What controls the frequency in this one is the 500kΩ variable resistor and the 1MΩ resistor connected to it (top center of the schematic) To achieve higher frequencies, lower the value of the 1MΩ resistor, and for lower frequencies, raise this resistor value. To achieve a larger sweep, get a larger valued variable resistor.

If I had to do this again (who am I kidding, I probably will!), I would change the 1MΩ resistor to a 300kΩ, and make the 500kΩ variable resistor a 5MΩ for a larger range, extending from 60Hz to 1KHz.

The math for all this is explained on this page (there's even a handy calculator at the very end if you're feeling adventurous enough to try even more values):

hi just built one of these, can anyone point me in the right direction to make a controller for it, cheers

dnhushak (author)  chris.collins.984991233 months ago

Do you mean MIDI controller? Or controller as in something other than just the knobs?

sorry, i meant controller as in cv gate or midi, something so that its not just the drone if that makes sense

ChadYoung1 year ago
Can anyone who's already successfully constructed this help me out? If you can, please respond to this comment with a Skype name or oovoo name or facebook or whatever. Thanks.
dnhushak (author)  ChadYoung1 year ago
ChadYoung1 year ago
Can you post a better picture or diagram of the circuit board that more clearly shows where I need to connect the wires to the board, potentiometers and audio/power jacks? Not a schematic, an actual picture or diagram. Thank you :) if you can do this, it would be a great help.
dnhushak (author)  ChadYoung1 year ago
The actual layout is totally dependent on whichever perf board you get. the physical components will lay out different for every different board, so it's best to just follow the schematic. If you're having trouble/don't know how to read a schematic, just view it as "every line is one electrical connection," so a line between two objects indicates a connection. If there is a third line going to the same line, that end of that particular component is also connected to the same point.
I'm using the exact same perf board you used. I've arranged and soldered the capacitors, resistors and amp to the board. I've also wired the audio jack to the board. My problem is that I can't figure out Where the potentiometers and power jack are wired to on the board based on the schematic. It's very unclear to me. Seriously, I would really appreciate a better picture of the wiring. I have a school deadline for this in two days. Thanks.
ChadYoung1 year ago
In the list of required items, you included 1k Ohm resistors. Then in the schematic they are replaced with 10k Ohm resistors. Which type am I supposed to use?
I think that the 10k resistors is correct. However, I have been trying to figure out if all of the resistors in the schematic are used. I am counting 8 on the breadboard, soldered board, and parts list, but there are 9 in the schematic. Am I looking at something wrong?
dnhushak (author)  pbowers31 year ago
The schematic is the correct one to follow. There should be 3 1MΩ resistors, not 2.
dnhushak (author)  ChadYoung1 year ago
For whatever reason instructables wasn't letting me post replies. 10kΩ resistors are what I use. Sorry for the discrepancy!
dnhushak (author) 1 year ago
Yes, one could, but then you'd have to have a separate set of circuitry to amplify the speaker. Best bet would be to find some cheap computer speakers, rip them apart, and use their amplifier and speaker in the box. If you can find a set of speakers that runs on a 9v power supply that's a bonus.
Mr Tesla1 year ago
Would you be able to make the box a bit bigger and include a basic speaker hooked up where the jack goes?
I know I didn't write this document, but I'm thinking that the answer to that is yes, yes you can.
pquadros1 year ago
Can you use an USB cable instead of the 9V power adapter?
dnhushak (author)  pquadros1 year ago
Theoretically, one could try it. Note that you'd only be getting 5V instead of 9V, so your op amp rails will only be ±2.5V, which doesn't give you much swing (and therefore not much output), but it's certainly worth a try. Let me know what results you get!
bengoza1 year ago
The ones in step four where you show the circuit laid out on a breadboard. Maybe they're not jumper cables, the thicker black and red wires going off screen. Thanks for the quick reply!
dnhushak (author)  bengoza1 year ago
Oh, two of those are going to a power supply to give the circuit the +9V it needs to operate - these are replaced by the power jack later on. The other two are going to an oscilloscope just to test output - these are replaced by the audio output jack later on. Hope that helps!
bengoza1 year ago
Where are those jumper cables connected to? What is their purpose? Thanks for your patience, and thank you for this instructable!
dnhushak (author)  bengoza1 year ago
Which jumper cables are you referring to?
jatinbatra2 years ago
what is peak voltage?
jin_yeugh2 years ago
I'm wondering where the other end of the 500k pot, from pin 2, goes. Do I take it to ground? it already goes to ground through the cap/resistor.
Skelpolu2 years ago
Hey there.
I'm a pretty much newbie in things like this. You will probably tell me to start of by soldering a working LED, but I've done that before. Anyway ...
I am not quite sure, but can't I also use a 12V Power Jack and a 12V LED-Power-Switch? ( It's just a switch with an LED indicating that its "on" ) I'd like to know. And also, another thing: The Schematic doesn't help me at all, I don't say its badly made, it's probably pretty good, but I don't know where what who is... If somebody can help me a bit more with that, I'd appreciate it a lot. See you then guys.
dnhushak (author)  Skelpolu2 years ago
Yep, a 12v switch with the LED will do just fine. The 12 supply can be the supply for the rails for the oscillator circuit as well, no problem.

Part of the problem with the schematic is that Instructables doesn't immediately show the image at full size. If you open the image, click on the little "I" in the top left corner of the image, and then click "view original file." This will let you see it in it's full size.

Past that, is the schematic unclear, or is it just an experience reading schematics issue? Let me know, I'd love to help!
Hi friend, could you tell me what voltage the capacitors are rated at?
dnhushak (author)  dnhushak2 years ago
Actually, sorry, the little i doesn't exist anymore for some reason.

That'll get you where you want to go.
Well, I've saved the full-sized-schematic btw, but my problem is that I don't understand it. I don't quite understand how those pieces form a Square-Wave for example. Nor do I know how to sold them now, the schematic looks complex for me. And like I said, I have no experience beside soldering an LED, which is pretty much pathetically-easy, eh? Anyway, perhaps we should talk about that using the PM-function to not spam this post?
jgierczak2 years ago
Is there an option to connect this little synth to sequencer?
oweng40003 years ago
Where's part 2?
dnhushak (author)  oweng40002 years ago
Haha, I'm working on getting something else up. I'm a EE student, so busy all the time!
gavox3 years ago
Any chance of getting a clearer schematic? can't see a blind thing on this one...
dnhushak (author)  gavox3 years ago

That should work.
gavox3 years ago would this op amp work? getting hold of the parts is quite difficult here in france, any way if this one doesn't work that you could find one that does on this website? thanks!
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