Novelty Synth from Recycled Vape
Today, we’re turning one of the most cursed objects of contemporary e-waste, a disposable vape, into a musical instrument. It’s like an ocarina, using your breath to activate and your fingers to control the pitch.
This project comes from my friends shuang cai, David Rios, and Kari Love. We gave a talk together at the Open Hardware Summit about reusing disposable vapes, and they’ve been conducting workshops around New York, teaching people how to build these. They’ve published a guide about the project on Instructables– this guide follows the same overall process, but in a slightly different order.
The existence of disposable vapes enrages me. They are designed to be thrown in the trash, and yet each one contains a rechargeable lithium battery, a charging circuit, a sensor, LEDs, and a surprisingly decent case. Previously, I made a video and a guide about how to harvest the batteries.
This project will reuse more than just the battery. We’ll use pretty much everything except the tank and heating coil. Just make sure the device is still operational before you go to the trouble of taking it apart. The battery will naturally lose charge over time, and if it was already low when left to sit for a long time, it might dip below a recoverable level of charge, and then it’s ruined. So I’ve made sure my target device at least lights up when I plug it in, indicating the battery is charging.
In addition to the parts we’ll get from the disposable vape, we’ll need a few photoresistors for the finger keys, a speaker to emit the sound, a 555 timer to generate the sound, and various components to support and connect all these parts.
Parts (DigiKey List):
- 1 – 555 timer IC
- 1- 1k Resistor
- 1 – 0.01 µF Capacitor
- 1 – 10µF Capacitor
- 6 – 10k CdS Photoresistors
- 1 – Thin Speaker
- Small Perforated Circuit Board
- Wire (Solid Core 22 gauge & stranded soft 30 gauge)
- Heat-resistant tape
Tools:
- Soldering iron
- Solder
- Wire strippers
- Flush cutters
- Pliers or tweezers
- Eye protection
- Workholding tool (often called a third hand)
- Multimeter (optional but useful)
- Heat gun (or a lighter)
- Solder wick or a desoldering pump for fixing mistakes
- 3D printer
- Small CNC Mill or Drill Press with step drill
- Deburring tool
- Box Cutter
- Metal Ruler
- Permanent marker or felt-tip pen
- USB-C Charger
- Mini Vise (optional)
- Hot glue gun and hot glue
- Toothpick
- Alligator clips
Open the Vape
The smoothest method for opening this type of disposable vape is to put it in a vise and pop the end caps with a chisel, then use pliers to gently pull out the internals.
Inside we’ll find: the battery, the charging board, the pressure sensor, and the juice cartridge with embedded heating coil.
The heating element and cartridge get discarded, and everything else becomes instrument parts.
Lithium battery safety warning: they can be a fire hazard if they short out or are punctured. I store mine inside a vented steel ammo box and then put that inside a fireproof bag. This tip comes from the Teardowns episode of my DigiKey series.
Additionally, this step should be performed in a well-ventilated space and while wearing gloves. Vape juice can be absorbed through your skin as well as your lungs. Wash the empty vape case with dish soap once it’s apart. Once the stinky tank is contained and the case is clean, you can remove your gloves.
Build the Circuit
Copy/edit this circuit on Tinkercad
At the heart of this circuit is a 555 timer oscillator. The team was inspired by a classic Forrest Mims circuit. The pitch is controlled by a resistor ladder made of photoresistors, a capacitor network, and the breath sensor, which acts as a gate. Light changes the resistance, which changes the frequency of the sound.
It’s best to build a solderless breadboard prototype of your circuit first, before trying to make it tiny and cram it inside the case.
I visited the Vape Synth workshop at my hackerspace, NYC Resistor, where the group walked through this prototyping step together. Success meant a sound was produced when the sensor was sucked upon. Alligator clips helped connect the components with smaller wires, like the speaker and battery.
Some attendees used buttons instead of photoresistors. Photoresistors produce a highly variable range of sounds, and Kari told me that some people prefer single notes, more like a true ocarina, not some ocarina-light-theramin. It depends on your musical taste. The circuit’s resistor ladder allows for this flexibility– you can use photoresistors or potentiometers for a fluid range of notes, or buttons and resistors to tune specific notes. Or even a combo of both.
To power the breadboard with the vape circuitry, connect the black battery ground wire to the breadboard’s ground, and the sensor output wire to the breadboard’s power– in these Elfbars, it’s usually blue.
The sensor reacts to low air pressure. Inside the original device, everything is gasketed up to create an airtight seal. Well, we are about to make a bunch of holes in the enclosure, so we’ll move the sensor to the mouthpiece instead of its original location at the bottom. I used a toothpick to hold it in place while applying hot glue.
You can use a can of compressed air to quickly cool hot glue, and the more you angle the can, the colder the air becomes because more of the propellant is released.
You can include the sensor’s original gasket and take advantage of the little pass-through channel, if you want to, or just stick the sensor in there by itself and intentionally leave a space unglued for air to pass. When done correctly, the power LED will light up when you suck on the mouthpiece.
I found that using the sensor alone resulted in a device that takes less effort to activate– not even a full breath, more like sucking on a drinking straw, whereas the original gasket with an air channel requires moving a lot of air (inhaling) to get going– your choice. You can always add more glue to further restrict airflow.
While our attention is on the original circuitry, it’s a good time to extend the charging board wires, since now that the sensor is in the mouthpiece, the wires are too short for it to reach the bottom, where it neatly clips into place. So I desoldered the three wires on the charging board and added some stranded wire to extend them. I insulated the solder connections with Kapton tape.
After wiring up the solderless breadboard circuit and connecting it to the vape circuit’s power output, you should hear a tone. If you only get popping, your capacitors might be swapped, and/or try shining a flashlight or other bright light source on your sensors. The ambient light is one of the ingredients impacting the final sound of the instrument.
So how do you find surplus disposable vapes? My friends know by now I work with these, so I have a whole bin of devices I’ve diverted from landfill. You can ask your neighbors in your local Buy Nothing group for theirs, or ask your local vape shop if they have a stash or if you can set up a collection box.
Once you have a working solderless breadboard circuit, you can get ready to build it into the case.
Modify the Case
We’ll need to make a few holes in the metal body of the case. One large one for the speaker, and six smaller holes for the finger keys.
I 3D printed these jigs from the tutorial that make it easier to position the case for drilling, or CNC-milling if you’re fancy. Shoutout to shuang, David, and Kari for publishing all these files for this project. Their Instructable for this project is *chef’s kiss*.
Before drilling, I used a center punch to dent the surface where each hole will be. This helps the drill bit bite in the right place, rather than dance around.
The angled jig is for the finger key holes, and the flat jig is for the center speaker hole.
I used my tiny drill press and a step drill to create the holes.
Afterwards, there are sharp burrs left inside the case, so I’ll use a deburring tool to remove them. Be careful not to apply too much force to the tool while working, so if it slips it doesn’t cut you.
Next it’s time to install the photoresistors. I splayed the leads flat and used Kapton tape to hold them in place.
Soldering inside the case can be tight, so I like to use my third hand tool to hold the case at just the right angle to see inside.
After the photoresistors are all soldered in series, with stranded wires added to each end, we can trim the extra leads and hot glue the sensors in place. The body of the case is metal, so be sure the leads don’t touch it, or it will affect the functioning of the resistor ladder.
Then it’s time to install the speaker. The hole doesn’t have to be big enough for the whole speaker to fit inside. You can drill a separate hole for the wires, if you want. I used a piece of tape to hold the speaker in place while the glue sets up. The hole provides a place for the glue to grab onto the back of the speaker, and provides some resonance as the sound bounces around inside.
The final version of the main 555 circuit takes shape on a small piece of perfboard.
Then I took the loose wires from the vape power circuit, resistor ladder, and speaker, and soldered them to the board, too.
Final Assembly
Before closing the case, test the circuit one last time. Once everything passes the functionality test, you can close it up inside the case. This is the most fiddly part of the project: fitting the battery and board inside the enclosure, which already has the sensors and speaker installed. Take your time, and use tools to reach where your fingers can’t.
Snap the end caps back on, and now you have a Vape Synth!
What I love about this project is that it doesn’t pretend reuse has to be invisible. It’s not trying to disguise the object. Instead, it’s calling attention to the fact that this thing existed and could have caused harm, but now it makes joyful music. I think that’s powerful.
