Getting started
Before you order parts, work out whether this build is for you, what you'll need on the bench, and roughly what it'll cost in money and time.
Is this for you
The OTP gadget is a hobbyist build. There's no PCB to fabricate and no custom electronics — you're wiring together a handful of off-the-shelf modules and housing them in a 3D-printed case. If you've built anything similar (a mech keyboard, a Pi-based project, a small synth, a flight-sim panel), you can build this.
You need a partner. A single gadget on its own does nothing useful — the whole point is two devices that talk only to each other. Plan to build at least two: one for you and one for whoever you'll exchange messages with. Build cost and effort below assume one device — double them for a pair.
You should be comfortable with:
- Following a wiring diagram and not mixing up power and ground.
- Soldering small through-hole pads. Nothing surface-mount, nothing fine-pitch.
- Running a 3D print and pulling supports without cracking the part.
- Flashing firmware over USB from a terminal.
If any of those are new to you, the build is still doable — it's just the first time you'll learn them. None of the steps are particularly hard.
Skills and tools
Tools you'll need on the bench (not in the parts pack):
- A 3D printer (or access to one). FDM, build volume at least 150 × 100 × 60 mm.
- A soldering iron with a fine tip, solder, and flux.
- A small Phillips screwdriver.
- Helping hands or a small vise.
- A USB-C data cable. Many cheap cables are charge-only — make sure yours does data.
- A multimeter. Optional, but useful for tracing wiring mistakes.
You don't need an oscilloscope, a logic analyser, a hot-air station, or a microscope.
Cost and time
Parts for one device land around USD 60–70 at retail, dominated by the Waveshare touchscreen module ($25) and the LiPo battery ($21). The rest is small: QR scanner, SD breakout, connector cable, and two MicroSD cards. Full breakdown with suppliers and SKUs is on the Bill of Materials page.
For a pair (the minimum useful build) you're at roughly USD 120–140 in parts, plus a few dollars of filament for the 3D-printed cases. The printable .3mf files are in the public repo for free.
Time-wise, expect a relaxed evening per device once the parts are on the desk: an hour to print and clean up the case, an hour to wire and solder, an hour to flash firmware and run setup. Faster if you've done a few of these; longer the first time.
Shipping is the bottleneck. The screen and SD module ship from China; the battery is RS Components; the cards are local. Order everything at the same time and plan for two to three weeks before you can start.
Building one
Ready to start? Head to Building one for the suggested order of operations, or jump straight to the Bill of Materials to start ordering parts.