Photo-Electric Piano DIY Soldering Kit Product Spotlight
Dustin van HooydonkShare
Light-Beam Piano
How it works · Build steps · Skill level · Kit contents · FAQ
No keys. No strings. Just seven invisible beams and the sound of something you built yourself.
The Photo-Electric Piano DIY Soldering Kit is one of those projects that makes people stop and ask: "Wait, how does that work?" You block a light beam with your finger, and the circuit plays a note. Block a different beam, get a different tone. It sounds like a trick, but every part of it is basic electronics: photosensitive sensors, resistors, a transistor, and a buzzer, all working together on a single PCB you solder yourself.
If you have one or two beginner kits under your belt and you are ready for something that feels genuinely different, this is a strong next step.
How the photo-electric piano works
What actually makes it play music? Here is how the circuit works.
The kit uses seven GL5516 LDR (light-dependent resistor) sensors, each paired with a small blue LED. The LED shines directly at its paired sensor. When the path is clear, the sensor sees the light and the circuit stays in one state. The moment you interrupt the beam with your finger, the resistance in that sensor branch changes. That change is picked up by the IC, which triggers the buzzer to output the corresponding tone for that "string."
Each of the seven sensor-LED pairs is tuned to a different note in the scale. The 12MHz crystal oscillator on the board keeps the timing precise, which is what makes the notes sound clean instead of drifting.
A single S8550 PNP transistor handles the speaker drive. This is the component that takes the signal from the IC and gives it enough current to actually push the buzzer cone and produce audible sound. Transistors doing exactly this kind of job appear in almost every audio circuit you will ever encounter, so seeing one here in a working context is genuinely useful.
The finished circuit runs on USB power (5V) or a compatible DC supply — no batteries to manage.
What You Build, Step by Step
This is a through-hole soldering kit. Every component has legs that pass through holes in the PCB and get soldered on the underside. It is the same technique used in beginner kits, but the component count is higher and the order of installation matters more.
The build follows a standard low-to-tall sequence:
Start with resistors. There are three value groups (1K, 4.7K, and 10K metal film), plus one carbon film resistor for the speaker drive branch. Resistors are not polarity-sensitive, but placing them in the right footprint matters — double-check the PCB silkscreen before each one.
Install the crystal oscillator and IC socket next. The socket goes in before the IC chip itself, which protects the chip from heat damage during soldering. Do not skip the socket and solder the IC directly.
The capacitors come after. The 10uF electrolytic caps are polarity-sensitive: the longer leg is positive, and the PCB marks the positive pad. Check both before soldering.
The seven blue LEDs and seven GL5516 photosensors are the most important step to get right. Each LED must face directly at its paired sensor across the board. They are installed horizontally, and the sensors get wrapped in heat-shrink tubing first to block ambient light interference. This is the step most builders find satisfying to complete — once those seven pairs are in place, the kit starts to look like what it is.
The transistor installs near the speaker footprint. The flat face of the TO-92 housing matches a marking on the PCB. Wrong orientation here means no sound, so check it twice.
Finally, install the speaker and power connector. Test before you close anything up.
Estimated build time: 2 to 3 hours for a confident beginner, around 90 minutes for someone with a few kits already done.
Is this kit right for your skill level?
Not sure if this kit is the right level for you? Here is an honest difficulty assessment.
This kit is labelled intermediate, and that rating is accurate. Here is what that means in practice.
You are ready for this kit if you have:
- Completed at least one through-hole soldering kit before (even a simple LED flasher counts)
- A temperature-controlled soldering iron (around 350°C is a good starting point for this kit)
- The patience to read the placement guide before each component, not after
You will find this kit challenging if you:
- Have never soldered before
- Are working with an unregulated iron and no temperature feedback
- Are prone to rushing polarity-sensitive components without double-checking
The sensor-LED alignment step in particular benefits from calm, deliberate work. If the LEDs and sensors are not aimed at each other cleanly, some notes will be unreliable or silent. It is not difficult to do correctly, but it is the step where shortcuts show up.
For absolute beginners, start with the Roulette LED Game Kit or a basic LED blinker kit. Come back to this one after that, and the build will feel manageable.
Who This Kit Is For
The second-kit builder
You finished your first project and enjoyed it. You want something that does more than blink. This kit gives you a working, playable instrument and introduces sensor-based circuits in a way that is concrete and immediately understandable.
The curious teenager or student
This kit tends to land well with people who are interested in both electronics and music, or who want to understand how sensors translate physical input into sound. The finished result is unusual enough to hold attention well past the build itself.
The gift buyer
If you are looking for a kit for someone who already has a bit of soldering experience and would appreciate something out of the ordinary, this is a solid choice. It ships from the Netherlands, arrives quickly across Europe, and comes with everything needed to complete the build (you will need a soldering iron and solder wire separately).
Kit Contents
The kit includes:
- Printed circuit board with full component silkscreen markings
- All components: resistors, capacitors, crystal oscillator, LDR sensors, LEDs, transistor, IC, speaker
- Heat-shrink tubing for sensor shielding
- USB power input support
- Printed assembly manual
Not included: soldering iron, solder wire, flush cutters. If you need a starter tool set, the tools collection at Slotman Customs covers the basics.
Frequently Asked Questions
Do I need to be able to play music to use this kit?
Not at all. The kit does not require musical knowledge. The seven beams correspond to the seven notes of a basic scale (Do through Do), and you just block whichever ones you want. Whether that produces actual music depends on the person holding their fingers in the beams, not on any prior skill.
What power supply does this kit use?
The kit runs on 5V DC. Many builders power it via a standard USB adapter. Check the product page for the exact connector type and voltage specs before powering on.
Is the IC chip included or do I need to source it separately?
The IC is included in the kit. You will need to install it after soldering all the other components, using the IC socket that solders into the board first. This is standard practice for kits that include programmable or sensitive chips.
Can I modify the kit after building it?
The notes are determined by the timing circuit and the fixed resistor values on the board. Changing individual resistors in the sensor branches can shift the response sensitivity of each string. Replacing the crystal oscillator with a different frequency value would alter pitch. These are intermediate to advanced modifications and are not covered by the standard assembly guide, but the circuit is simple enough that someone comfortable reading a schematic can explore from there.
How long does shipping to the Netherlands take?
Slotman Customs ships from Haaksbergen in the Netherlands. Domestic orders typically arrive within 1 to 3 business days. European delivery times vary by destination. Check the shipping information page for current estimates.
Ready to Build?
The Photo-Electric Piano kit is available now in the Slotman Customs web shop. Ships from the Netherlands across Europe.
