Show HN: Simulated transistor animations render electrons, holes, and recombination

A developer built a semiconductor simulator and used it to animate how charge carriers move through three fundamental transistor types: the NPN bipolar junction transistor, the n-channel MOSFET, and the n-channel JFET. In the visualizations, blue dots stand in for electrons and red dots for holes, while white flashes mark recombination events where the two annihilate. It’s an attempt to make the normally invisible physics of solid-state devices legible.

The animations come in three tiers of fidelity. The first set moves carriers at a velocity derived from the combined drift and diffusion currents divided by total charge, omitting diffusion as a visible effect for clarity. The second set adds explicit drift and diffusion motion — the physically most accurate depiction, though the author concedes it looks noisier and harder to follow. A final set overlays probes showing the currents and voltages at each device terminal, tying the microscopic carrier motion back to the measurable electrical behavior an engineer would see.

The project is educational rather than commercial, aimed at anyone trying to build intuition for how transistors actually work at the carrier level. By offering the same devices at escalating levels of realism, it lets viewers trade visual simplicity for physical accuracy depending on what they’re trying to learn.