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Cake day: June 10th, 2023

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  • When you come across some Python code for something written 5 years ago and they used four contributed packages that the programmers have changed the API on three times since then, you want to set up a virtual environment that contains those specific versions so you can at least see how it worked at that time. A small part of this headache comes from Python itself mutating, but the bulk of the problem is the imported user-contributed packages that multiply the functionality of Python.

    To be sure, it would be nice if those programmers were all dedicated to updating their code, but with hundreds of thousands of packages that could be imported written by volunteers, you can’t afford to expect all of them them to stop innovating or even to continue maintaining past projects for your benefit.

    If you have the itch to fix something old so it works in the latest versions of everything, you have that option… but it is really hard to do that if you cannot see it working as it was designed to work when it was built.







  • Resistance is like shocks on a car… push hard to compress and it compresses faster. push less hard (voltage) and it doesn’t move as fast (current). Pull it (negative voltage) and it expands (current flowing the other way). Resistors resist (voltage against) flow (current).

    Capacitors you sorta seem to get: current flowing in one direction through a capacitor builds up voltage the remains after the current stops… like the force in a spring builds up as it compresses and when the motion stops the force is still there.

    What you seem to confuse with resistance is inductance, where the force (voltage) on an air hockey puck makes it speed up (current flow), and when the force stops pushing it it just keeps moving (current keeps flowing).

    The general term for these voltage-current relationships is impedance, because in the general case where voltage or current is oscillating or rapidly switching on and off you get some effects that resemble resistance (voltage pushing back on current or vice versa).

    Final concept is that any time you have something trying to force specific levels of current or voltage on a pin, the “setter” (whatever is doing the forcing, typically referred to as the “source”) has impedance and so does the “getter” (whatever is being forced, referred to as the “load”). If you have a fishing rod and you want the tip to move slowly, you can easily move it where you want it to go, but if you want to shake it fast it won’t move as far (the weight of the tip is like inductance resisting the motion with force/voltage).

    So, a microchip pin might have high resistance to ground but also high capacitance to ground… and a quick pulse of voltage will immediately cause current to flow into the empty capacitor, and if the capacitance is big enough the voltage won’t change much, or will require more time to change. High capacitance has low impedance… it sucks up any available current as the desired change in voltage happens. interestingly, there are two options for making the pin voltage change faster… increase the current level being used by the source (by reducing impedance within the source so it can get out to the pin easier), or reducing the amount of current required to change the pin voltage by raising the impedance to ground inside the chip package (that is, reducing the capacitance inside the chip package).

    When the source impedance is very very large, that is like having the signal generator probe laying on the bench instead of connected to the pin. When the source impedance is large and the internal pin impedance is large, then any stray electric or magnetic fields can push the pin voltage around easily. This is what they call floating… and if the microchip is reacting to those erratic voltage signals then the circuit as a whole will behave erratically as it tries to react to noisy input.

    An output pin usually (but not always) has a lower source impedance than a tri-state input in its high impedance state. If you connect it to a floating input then the input stops floating and follows whatever the source is forcing it to.

    An input pin usually has an input impedance similar to the source impedance of sources connected to it… this generally allows the input to be controlled most quickly. Inputs whose voltage doesn’t change quickly tend to be less useful than ones the do change quickly bandwidth and clock speeds can be faster.

    If you try to connect microchips built with different technologies together (e.g. CMOS vs TTL) then they may not communicate quickly or with minimal wasted power because they have different typical impedances (and voltage levels).


  • I view college as training for dealing with deadlines and some logic practice (e.g. this essay isn’t coherent; math exam next Wednesday). I never see people come through the door ready to go… it takes a few weeks before even the most basic tasks can be delegated. Their writing still sucks 90% of the time, and their math is usually shaky (lucky we have automated many steps with computers.)

    I agree that the pace at which all this goes is exhausting and more breaks are needed, but the third world is still full of people working overtime to overtake these “professional” jobs that colleges purport to prep workers for. Don’t go to an overpriced Ivy League school and take on debt and expect a 20h week… go to a govt sponsored school and be prepared to compete with the remote workers working for the company that is undercutting your employer. Welcome to globalization.





  • Pretty vague question.

    One assumption that “mathy types” like to make is that the slope be negative-proportional to how far the value (not slope) is from the desired target value… and then you get an exponential decay (buzzword). But there are lots of other assumptions one could make… some of which lead to PID control (buzz; very mathy stuff).

    But these days you could use a neural net (buzz; so mathy they don’t usually pretend to understand what the NN “learns”) or fuzzy logic (buzz; which is ideally intuitive but has many surprisingly mathy assumptions) to make the behavior nonlinear and go to the desired result much faster… so really, there are many many possible answers. Maybe you can watch some ELI5 videos about these buzzwords and refine your question?