Pocket Sized Synthesizer




This small-but-mighty pocket synthesizer can be used to play that tune that is stuck in your head on-the-go, scare away unwanted animals, or to annoy the heck out of your friends and family. The tone is a square wave and depending on what value of the potentiometer you use you can achieve a 6 octave range. Secured in an Altoids mint tin, this device is truly pocket-sized. Lets get started! 
1x push button switch
1x 100 ohm resistor
1x 220 ohm resistor
1x NE555 timer chip
1x mini speaker
1x 1uf-100uf capacitor
1x 2.2uf capacitor
1x photocell
1x 9v battery and clip
1x bright white or blue LED
Some perfboard, solder, soldering iron, and wire

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Step 1: The Basics

So how does this thing work? When it comes down to it, it is an astable 555 timer circuit. The LED is placed so that it shines on the photocell. Depending on the strength of the LED, the photocell sends a frequency to the speaker which then emits a sound. The LED is dimmed and brightened by the potentiometer which in turn varies the frequency that comes out of the speaker. A capacitor takes out the DC which comes from the output pin (pin 3) of the NE555 chip which then runs to the speaker. The other end of the speaker is grounded. Now that you know how it works, you are ready to build it!  

Step 2: The Schematic

A few things to remember:
The photocell value doesn't matter, just use one that can get enough light.
I tried using a 4.7uf capacitor in place of the 100uf capacitor and it worked fine. My point is that this is a flexible circuit. Don't be afraid to substitute parts to find what works best for you.
I would use a 2.2uf capacitor for the 1uf-10uf capacitor.
The speaker doesn't have to be 16 ohms, but it works the best.
PLEASE use a bright LED. It will make your life so much easier (and give the synthesizer the best sound).
Build this on a breadboard before you put it on perfboard.

Step 3: Put It Together!

Not much to say here, just put it on a perfboard and into the mint tin! Make sure you face the LED to the photocell so you can get a good sound. If you have any questions, please leave a comment. This is my first instructable so please try to hold your punches. Have fun!

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    11 Discussions


    6 years ago on Introduction

    I love this thing so much. The only weird thing is, sitting in class making these noises with my hand down my pants.

    1 reply

    ha to make it even louder take out the led, and put the variable resistor in place of the photocell
    it is then screaming loud

    What are you having trouble with? I have made a video on how to build this on a breadboard: http://www.youtube.com/watch?v=t6oi_fKhjf0
    If this doesn't help, omit the LED, potentiometer, and the photo resistor; replace the photo resistor with the potentiometer
    hope this helps


    Your shorts on the table? That was truly strange.
    It's an Altoids box. I think we know it can fit into even jean pockets, not just huge basketball shorts. That was so strange. hahaha

    1 reply

    7 years ago on Step 3

    Good first Instructible.

    Some comments:
    Why are you using the LED and photocell when you could simple use a pot in the place of R1 where you have the LED? This would make the battery last longer and would still sound the same.
    I thought you might be using the photocell to make a light controlled Theremin where you could vary the light falling on it with a shadow from your hand. Have you tried this?
    Also, photocell can be a confusing term as it is used for various devices. Did you mean the type that generates electricity (a solar cell type) or a light dependent resistor (LDR)? Usually an LDR is used here but I suspect either will work and small solar cells are easy to come by from solar garden lights .
    A perfboard layout would also help some beginners too or a photo of the board showing components before it was placed in the Altoid tin.

    Keep on having fun!

    2 replies

    The photocell is a solar cell type, but i have tried it with the LDR and somehow it works (but the tone is not as loud). I have also tried using a joule thief set up with a 1 megaohm resistor between the positive and the joule thief. This seems to make the LED brighter, and it also saves the battery by limiting current. I also used the LED and the photocell because you can learn how a 555 oscillator and a photocell work. It is fun to build and you can use different colored LEDs to make different pitches. Take a look at this video I made on how to build this on a breadboard for beginners:
    I should have put this in with the instructable, but i didn't want to because people would just look at the video.
    Thanks for the advice!


    Thanks for the reply and comprehensive explanation of your design choices. I think it's good to include the perfboard video as well- I gave it a thumbs up!