July 1, 2026
Tape, water, and transistor tears
Homemade Transistor from Cadmium Sulfide Photocell (2009)
A garage-built light sensor turned into a DIY switch, and the comments went full mad scientist
TLDR: A hobbyist turned a common light sensor into a homemade electronic switch using tape and a drop of water, showing a surprisingly simple DIY breakthrough. Commenters loved the mad-science energy but immediately argued over safer materials, better design choices, and whether the whole thing is just too slow to be truly useful.
A 2009 hobby electronics post just resurfaced and honestly? The real show is the crowd reaction. The original experiment is wonderfully chaotic: radio enthusiast Nyle Steiner took a common light-sensitive part, slapped on Scotch tape, added a drop of water, and managed to make it behave like a transistor-like electronic switch in the dark. It’s the kind of kitchen-table science that makes the internet collectively yell, “Wait… that actually worked?” You can read the original write-up here.
But the comments are where the popcorn starts flying. One user immediately went into full home-lab mode, asking if anyone had tried it, why black tape wasn’t used, and whether sanding off the coating would bring the voltage down to something friendlier like 9 volts. That set the mood perfectly: half impressed, half “I can fix this in my garage.” There’s also a clear undercurrent of safety anxiety—because whenever a post includes improvised parts, water, and electricity, somebody is going to ask for “better, safer ways” before the rest of the thread accidentally invents a fire hazard.
Then came the performance snark. Another commenter cut straight to the weak point: these light-sensitive parts are slow—“like 0.1s slow”—raising the brutal question of whether this thing is clever science, or just a glorified proof-of-concept that reacts like it’s buffering on bad Wi‑Fi. The vibe is classic internet maker culture: admiration, nitpicking, and a little roast on the side.
Key Points
- •The article describes a 2009 experiment in which a cadmium sulfide photocell was modified to show field-effect transistor-like behavior.
- •The improvised gate was made by placing Scotch tape over the photocell, adding a drop of water as a conductive layer, and touching the water with a wire.
- •Steiner reports that the setup produced transistor action when operated in the dark, while normal light saturated the photocell and largely eliminated the effect.
- •Earlier attempts using charged objects near the photocell or catwhisker devices were deemed inconclusive because of light interference or physical movement.
- •The reported device had considerable power gain, very low voltage gain, and an effectively infinite gate input resistance limited mainly by leakage through the tape.