Intro: 555 Pocket Synth/Keyboard
Hello! Welcome to my instructable. Before we begin talking about how to build this synth, Ill present the basic skills and knowledge that is required... You should know these things:
- What a resistor is
- How to solder (semi-decently)
That's really all you must know to put this noise-maker together, but it really does help to know about capacitors, potentiometers, and a little music theory. Although this synth only uses simple components, it is a great toy that can provide many hours of enjoyment (to the right person).
I have to give credit to one site, for this was not entirely my idea. The schematic that inspired me to make this is here. After implementing that schematic on a breadboard, I wanted to make a bit more advanced version of it, that was portable... and shaped strangely like the Instructables' Robot.
Thanks for your interest. Lets begin!
Step 1: Parts and Pieces
List of parts:
-100k Potentiometer (higher values are OK too)
-10k Potentiometer (Lower values are actually more optimal)
-13 2.2k resistors (you can really use any value between 1k and 5k as long as they are all the same value)
-1 4.7k resistor
-1 330 ohm resistor (450 ohm or higher is more optimal but 330 ohm works)
-8 Ohm Speaker (or buzzer/piezo)
-two-way slide switch
-13 tactile buttons
-9v Battery (with connector)
-perfboard (I used a 5cm by 7cm piece)
List of tools:
-Soldering Iron (and solder rosin)
-Hot Glue Gun
-Optional: Desoldering Iron
While gathering the parts, keep in mind that many of these parts don't need to be exact. Most resistor values can be a few ohms off. Same with the potentiometers. You can make this circuit with only 50k or 10k potentiometers if you'd like and it would function almost the same as the one I'm describing in these instructions.
Step 2: Breadboard It!
Once all of the parts are at hand, its time to put them into a breadboard. Here is a link to the schematic. I have also uploaded it from the original website, 555-timer-circuits.com. If you are new to schematics, don't be afraid it is rather easy after you learn what each component is represented by. Wikipedia is a great source for that. I have attached pictures of my breadboard implementation, as well as a video of the working circuit.
We are not going to create the exact circuit in the schematic please take note of these changes I made:
-I changed the 1k resistors to 2.2k resistors for a bit more accurate half note production (we will learn more about this below).
-Replaced the 10k potentiometer with a 100k potentiometer (for a more extreme pitch bend).
-Added a 10k potentiometer between pin 3 and the 8 ohm speaker (functions as a volume control).
-Added 9 more buttons in series with the ones on the schematic. (Just continue the pattern of one tactile switch connected to a resistor). However, don't worry about this until you solder the perfboard. For the breadboard, just try to add 4 or 5 buttons.
-Added a indicator LED from the 9v rail, connected to the 330 ohm resistor which finally goes to ground. (the resistor value really should be 450 ohm, but 330 ohm is close enough for our purposes).
-Also as a optional step, I added a two way slide switch between the first tactile button and the potentiometer (which acts as a sustained note).
Keep in mind:
It may be useful to keep this circuit on the breadboard for when you solder the final version. It will be nice to have a working circuit to use as a reference. So don't take it apart until you finished the soldering! (Unless you're short on components).
The circuit basically sets the 555 timer into a mode where it outputs a square wave at a frequency based on the voltage on one of its pins. When a tactile button is pressed, it adds the previous resistor values (since they are in series) to make a change of resistance which we want to be equal to one half-step (in music theory terms) between each button. In this circuit, the lower the resistance the higher the frequency produced.
Disclaimer: If you look at this chart. You'll see that the difference between frequency and musical note produced gets larger as the note gets higher. Therefore, this synth will NOT have accurate half-steps between each button. But as you adjust the pitch bend potentiometer you can achieve something sort of close.
This voltage based system is pretty effective for this synth; however, here are the drawbacks:
-the frequency of each note changes based on the battery.
-using the "pitch-bend" knob (100k pot) changes the frequency it takes for each half-step. So using it changes notes strangely. However, you will find that there is a sweet-spot where most of the buttons will produce roughly a half-step up/down from the previous.
-using the volume knob (10k pot) bends the frequency each note, since it varies the voltage drop across the speaker.
-It forces the synth to be monophonic (produce only one note). While this isn't entirely the voltage system's fault, it is a reality of this circuit. However, this can be a desired sound for some and can produce cool effects.
Challenge for more advanced hobbyists:
For those of you more experienced I challenge you to fix these problems and post your solutions in the comments. (Maybe use a voltage regulator? or variable resistors?)
Once you have this circuit running on the breadboard, and have at least a rough understanding of whats happening behind this circuit, we can put this on some perfboard!
Step 3: Plan the Perf!
As I mentioned before, I made this so that it could be a fun and portable synth. Lets address the layout of the synth to make it as easy to play as possible. The layout I liked the best strangely resembled the mascot of instructables.com... well at least to me it did. (the potientiometers are the eyes and the buttons the mouth). Anyway! I encourage you to deviate from my design choice; however, as you'll see on the video in the final step, my layout is quite playable.
The pictures attached show my thought process (which isn't really complicated). Keep in mind that I only put the components through the perfboard, I haven't soldered them just yet. Also, I have left out the resistors and capacitors while planning this step since I'd rather imagine them there than have to put them all in.
Step 4: Time to Solder!
After finding the perfect perfboard layout, you can begin by soldering everything that you are absolutely positive about onto the board. Desoldering isn't all that fun so make sure you try to get things right the first or second time. I have attached a picture of my soldering job, but it doesn't look too pretty since I never took the time to touch it up. I won't go over what to do with each component when soldering since your layout may be different than mine, and that would take forever. However, I will tell you some tips I've learned from soldering:
-Keep your breadboard implementation nearby while soldering so you have a reference other than the schematic to use.
-When soldering a component with more than one lead (or pin), to ensure that it is soldered tightly to the perfboard, solder one lead (or pin) onto the board first. Then check if the component is straight, if its not then heat the lead and adjust until it is. This technique is a lot more effective than soldering in an entire 8 pin integrated circuit (such as the 555), then learning that it isn't in the perfboard straight.
-Get a desoldering iron. These are optional, but highly recommended. They are good for salvaging parts off of electronics and fixing major mishaps in your projects.
-Use resistor's long leads to make connections. It is a lot more efficient than using tons of wires.
-Use lots of hot glue to ensure that your circuit is permanent and to keep resistor leads from touching other components/conductive surfaces.
-Use an exacto knife (or any knife) to troubleshoot for shorts. I always run a knife between suspicious connections that may be touching, to scrape away any excess metal that may be joining them.
-Remember electrolytic capacitors have a negative lead and a positive lead, while ceramics do not.
-Try not to touch the tip.
Be sure to mind the additions I have made to the schematic! Refer back to Step 2 for reminders.
Step 5: Add a Case!
Congratulations, your synth should now be functioning! However, if you press your fingers against the solder joints you will probably hear a very low frequency sound (due to the resistance of your finger, I believe). To prevent this you will need to build a case. You could do anything from an entire case, to just a back panel. I was so excited to get this thing functioning that I simply screwed in a sheet of acrylic to the back of the synth to protect it. Get creative with it and share your case designs with me, and in the comments!
Step 6: Play It!
Finally, you should have a working pocket sized synthesizer/keyboard! While the intonation on it is not perfect, (and rather crazy at times), it is a fun toy and a truly playable instrument. I have already played hours on it and learned a few songs. Learning to play on it was different than any other instrument since it is unpredictable and can add a twist onto what notes you play, which can be very interesting. I hope you've learned a bit about how electronics interact with sound production, and enjoy your pocket-sized synth!