Introduction: 555 Pocket Synth/Keyboard

Picture of 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:

- Ohm's Law

- 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

Picture of Parts and Pieces

List of parts:

-555 Timer

-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

-an LED

-13 tactile buttons

-100nF capacitor

-10uF capacitor

-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!

Picture of 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!

Picture of 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!

Picture of 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!

Picture of 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!

Picture of 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!

Comments

crazyscottnb (author)2014-05-26

SOOOO cute I love it, gona try this one for sure, although would suggest using different switches, maby use these kind of switches

http://www.jaycar.com.au/productView.asp?ID=SM1038

Tanmayg (author)crazyscottnb2015-04-05

they are the best

LaserDave (author)crazyscottnb2014-05-27

Although switches like that would be nice, a budget-concious design like this would be difficult to justify at around $5 per switch.

A better alternative would be to use these tactile switches (at around $0.50 each) with an arm mounted over them to mimic piano keys, or the switches you suggest.

Simply place the tactile switches under an arm (like a popsicle stick) hinged at one end so that pressing down on it will push the switch. Mounting them all in a straight line will create an inexpensive, yet effective, keyboard.

bergerab (author)crazyscottnb2014-05-26

Wow excellent idea! That really enhances the playability, thanks for your contribution!

georgemorgan (author)2014-05-29

This is Very cool :)

Thanks

krm_priya (author)2014-05-28

I made this on a breadboard but the speaker isn't responding.

Is it because I have used a preset instead of a pot?

bergerab (author)krm_priya2014-05-28

As long as the trimmer is 10k, it should function as a potentiometer in this configuration. Make sure you have connected pins 6 and 2 together, and 8 and 4. That was the solution for me when the speaker wouldn't respond. Also try the circuit without any trimmers/potentiometers to eliminate any problems they could cause. Let me know how it goes!

Jan_Henrik (author)2014-05-27

AWESOME! :D very cool!!

mgoel (author)2014-05-26

So to add more switches for the notes....i extend the circuit in the same manner as shown in the diagram????

bergerab (author)mgoel2014-05-26

Exactly! Since the resistors are in series, each note you add will be a lower frequency from the last

mgoel (author)bergerab2014-05-27

thanx.....going to try it this week!!

samuraijack (author)2014-05-25

i like it.

there is always room for improvement in all things,

but if it works why fix it ? :P

RG_on_the_move (author)2014-05-25

I cannot wait to try to make this. I can only hope my solders turn out half this good!

bergerab (author)RG_on_the_move2014-05-25

Thanks so much for your interest! Let me know if there's any additional information that should be in this instructable. Goodluck!

ToggleSwitch (author)2017-06-02

Hi!!! :/) I have made a 555 timer keyboard very similar to this, but rather than staying silent until I press a button, it makes noise as soon as I start it. All the buttons function properly, raising the note in intervals but it starts with sound. I have thoroughly searched my button/resistor series for accidental bridges between joints but have found none. This is my first "real" soldering/perfboard projects, so mistakes could have been made! Could there be any other reason for this noise? I cannot find somewhere else where the circuit may be completing. Any help would be appreciated :~)

k-a-project made it! (author)2015-12-02

Thanks for your help, this is my version with 6 notes :)

biraj1002 (author)2014-05-28

i made it but it wont work please tell me what mistake i made. U DONT MAINTION THE 100uF & 10uF capasitor which side goes to the positive and negative in the diagram tell me urgentely

htownclyde (author)biraj10022015-06-12

ceramic disc capacitor is non-polarized

titch16 (author)biraj10022014-06-09

There is a white line on the negative side.

ToggleSwitch (author)2015-06-02

If anyone could help me I am very new to these types of things and i was wondering. If i wanted to make this but make it sound like a guitar (or for these purposes change the sound in any way other than volume of the pitch bend) how would i do this? Is there a certain chip I can use? or is it more comlicated than that? If anyone can take time to answer these questions I would greatly appreciate it :).

bergerab (author)ToggleSwitch2015-06-03

A 555 chip, no matter what you do with it won't sound much like a guitar. If you're looking to make a guitar sounding synth I would consider looking at microcontrollers or an actual synth chip. Since microcontrollers are pretty easy to use I'd suggest that over the synth chip. To make this simple, you could use an arduino uno or mega to do the project. You would need digital samples of a guitar. You can obtain these by either making them yourself (if you own a guitar and an audio interface) or finding them online. Then you'd have to use software on your computer to compress the audio to an 8 bit sound file and extract the bytes from it and enter them into the arduino as a byte array. Next, you would need to make a Digital to Analog Converter (DAC) to turn those bytes into an actual analog signal and connect that to 8 digital pins on the arduino. Finally, you would have to attach a few buttons to your arduino (to maximize digital button inputs you can use a shift register - - I. E. 74HC595) and press them to trigger these samples. This would make an 8-bit guitar sounding synth and you could even add different effects onto it too. Good luck!

ToggleSwitch (author)bergerab2015-06-03

Great! Thanks so much for the help!

Victor805 made it! (author)2014-08-23

Thanks for making ths instructable, now I have a portable 8-bit synth.

I used some electronic scrap I had laying around, the buttons are kinda faulty, they only have 2 legs causing worse connections, I'll fix that by buying better ones. Using 2.2k resistors has been a great idea, I dislike pitchy tones.

I also plan to add an output jack by connecting it to the speaker output and using some pins and jumpers to select the output mode.

I ended changing the 10k potentiometer for a 200 Ohms one because I used a 4 Ohms speaker and the 10k potentiometer was way too big, it doesn't turns off the speaker completely but it's easier to adjust since the biggest voltage drop is produced around the 100 Ohms.

Victor805 (author)2014-07-29

Sounds great, I'll make one for a friend of mine who is into music.

shaldar2 (author)2014-07-27

My version
very good instructable made it in my first go thanks.........!

brmarcum (author)2014-06-29

I thought about making something like this for my kids a couple of years ago. Good design and very simple and easy to make.

rverdugo (author)2014-06-03

amigo yo hice el sintetizador, y es maravilloso saludos!!

PD: hice el del primer esquema :D

nqtronix (author)2014-05-25

I don't know you personally so I judge by the work I see. And that honestly is everything but good. The fact that put the LED in series to the whole remaining circuit proves that you lack on basic knowledge. But I don't blame you, 80% of all beginner circuits you can find on the internet aren't better at all. That's quite a shame because learning how to do things right gets harder. My attempt is to correct at least all mistakes on popular instructables to help not only the author, but also the people reading the instructables.

In search of a simple transistor amplifier I stumbled across this instructable ("A Stylophone") which has a really practical circuit. Even though it does not contain what I was looking for, the NE555 is used in a very clever way (I've never used one so I can't tell you about any personal experiences, but I know the theoretical operation). The LM386 is a specially designed audio amplifirer to work with just a very few external components. The circuit is directly taken from the datasheet so I assume it works realy well. I've unfortunatly no LM386 at home, so I can't try it out myself. Since you know about voltage regulators I don't think schematics are nesessary. The LED should be direktly connected to the voltage regulators output in series with a resistor (@5V with a standard LED 150R are fine, 180R best and anything larger should work with a dimmer light) to ground. If you have still any questions don't hesitate to ask.

And no, I'm not (yet) an engineer, I'm some random guy, who just finished high school. But I'll take the compliment :D

- nqtronix

biraj1002 (author)nqtronix2014-06-02

I love it. I have make one. It's works good. Thanks

bergerab (author)2014-05-28

Actually if you look in the schematic it does show the polarity for the 10uF cap. On pin three have current flow through the negative side, then positive and finally attach that to the speaker. And the 100nF cap is not polarized so it doesn't matter which side goes where. Also if your synth isn't working, make sure you connected pin 6 and 2 together as well as 8 and 4. Those are necessary connections but they are easy to miss. Good luck!

pvalyk (author)2014-05-25

I love chaos! :D

nqtronix (author)2014-05-25

I've no idea to say this nicely but...

Your soldering skills are not even "semi-decently" but really crusty. The placement of the components is just as poor, it increases the mess to an unacceptable level. There's a lot of room for improvement:

Spend some good time before soldering the first component into place about the whole layout. Most important is the placement all user-accessible parts such as knobs, buttons, plugs or headers as it directly affects the usability. Next you try to place all remaining componets on the board. Try to keep all connections as short as possible and preferable without crossing.

Short all leads of the components to be just as long as needed. If the components don't "snap in" position bend the leads just untill they barely hold in place. Solder then all parts in, but only two leads per component.Doing this you can reheat on pin to push the component flat against the board before solder the remaining pins. At last solder all connections in place. With this method desoldering is an ease, you don't even need anything else then the soldering iron you've just worked with. Reheat a pin and use a screwdriver to pry out the part. This works also on ICs , but you have to reheat one half (I did that with quite large packages like a DIP-28).

---------------------------------------------

Concerning the problems you wrote about:

1. A simple voltage regulator like the 7805 (google it) + a litte capacitor (10u) will do the job. Do note that the maximum volume will also be limited.

2. The "pinch-bend" knob does exactly what I thing it should do. A little more explaination what you have thought of would be nice.

3. The potentiometer should be used as a "voltage devider" (if you have never heard of that, google it. It's the simples and most used circuit block) followed by an amplifier circuit. This can be as simple as an additional transistor plus a (few) resistor(s).

4. Creating multiple tones at once is a rather complex task or at least way to complex for you right now. This circuit can't be modified to fullfill this task. However I assume you'll find a suitable solution relativly quick just by asking your friend google ;)

In addition: The power idicator LED isn't connected as it should be. The LED should be in parallel to the whole circuit (with a protection resitor of course) and not(!) in series.

---------------------------------------------

For now, that's it. Depending on my mood tomorrow I'll add schematics to all the improvements I suggested. I'm sorry I can't do it now but I'm about to fall asleep ;)

PS: Don't get me wrong, I started just like you and I did just as much mistakes as you did. Nobody masters anything right from the beginning ;)

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Bio: I'm a student at UW-Milwaukee studying computer science with a passion for electronics. I'm always working on a project or thinking of new ... More »
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