Show HN: I made some transistor animations

Oh, yes. I updated the page so the animations are now under the CC-BY license. Glad to hear you like them!

You can google for "From nand to tetris" or get the book Digital Design and Computer Architecture by Harris to get the idea of how these machines work.

1. I wouldn't be able to do that because these examples are only available in the desktop/steam version.

2. Again this is feature is in the desktop version only (check "View charge carriers"). You can reverse the voltage source by setting the voltage negative.

3. That's a nice suggestion, I think I'll implement it in the next release.

I have no plans to update the web version any further.

> between the current (as in BJT) and the voltage (as in field transistor and valves)

The BJT is also much more accurately modeled as a device where the collector current is determined by the input voltage (i.e. base-emitter voltage), exactly like the vacuum tubes and the field-effect transistors.

There are however a few reasons why their description as being controlled by the input current is preferred in popular literature.

One is that the dependence between output current and input voltage is more strongly nonlinear than for vacuum tubes and FETs, i.e. it is exponential instead of being polynomial, so it can be approximated as linear only for very small voltage differences, of a few millivolt.

On the other hand there exists a relatively small current range where the collector current depends linearly on the base current, which is useful for mental approximate computations of a circuit with BJTs. But it must be kept in mind that this approximation is not useful for accurate circuit design, because beta (the ratio between the collector current and the base current) instead of being a constant it drops quickly both at big collector currents and at small collector currents.

Besides the great non-linearity of the output current/input voltage dependence and the approximate linearity of the output current/input current dependence, the other reason why BJTs are frequently described as "current-controlled", instead of the more appropriate "voltage-controlled", is that their input has a great leakage current (i.e. the base current), while the leakage currents of the inputs of vacuum tubes and FETs are so small that they are normally negligible.

In conclusion, one may prefer to use the description of the BJTs as "current controlled", but one must be aware of the serious limitations of this point of view. Even for mental computations, it is more useful to use the beta value of a BJT not for computing a fictive current gain, but to compute the input leakage current of the BJT conceived as a transconductance amplifier (unlike beta, which varies from transistor to transistor, the transconductance gain is the same for all BJTs), to be used for computing voltage drops in input resistor networks.

The animated visualizations are nice, but the only way to easily assess the quantitative differences between various types of BJTs, FETs and vacuum tubes is to draw the families of curves that show the output current from output voltage dependence, having as family parameter the input voltage (and also the family of curves obtained by interchanging the output voltage and the input voltage between graph axis and curve family parameter). (These families of curves being sections of the 3D surface of the graph of the output current as a function of input voltage and output voltage, but a 3D graph does not allow a precise comparison of the values in different points.)

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The simulation does calculations on the fields only, so it keeps track of the average electron and hole density at each point in space. There is, however, a one-to-one correspondence between the behavior of the fields and the motion of individual particles, which is what makes these animations possible. What I mean by this is the diffusion equation is satisfied by the probability density of a particle undergoing a random walk. So given an electron density that obeys the diffusion-drift equations we can make dots undergo a random walk with drift that turns out to match the given density function (the result is the second set of animations).

I think universities are missing a course on writing a simulator of all the things you learned, e.g. Maxwell's equations and semiconductor physics for EE.

Not too difficult. Stay tuned for the 3D version.

Additional things to model with an electron simulator or a particle simulator; concept sustainable computing materials from my sustainablefactory project:

- Electrons in laser-induced Graphene on Silicon Carbide

- Electrons in Boronated Lignin-Vitrimer

- Photons in Nitrogenated Lignin-Vitrimer (at cryogenic temperatures)

- Electrons in Oxidized Carbon Nanotubes (in Laser-ablated grooves in Nitrogenated Lignin-Vitrimer) after Laser Compression Shock bonds and deoxidizes them

- Boron Nanotubes; Boron nitride nanotubes (BNNTs)

- Boron instead of Phosphorous for P-type doping

- Boron instead of Gallium in GaN