[Prof MAD] runs us through The Hidden Power of Inductors — Why Coils Resist Change.

The less often used of the passive components, the humble and mysterious inductor is the subject of this video. The essence of inductance is a conductor’s tendency to resist changes in current. When the current is steady it is invisible, but when current changes an inductor pushes back. The good old waterwheel analogy is given to explain what an inductor’s effect is like.

There are three things to notice about the effect of an inductor: increases in current are delayed, decreases in current are delayed, and when there is no change in current there is no noticeable effect. The inductor doesn’t resist current flow, but it does resist changes in current flow. This resistive effect only occurs when current is changing, and it is known as “inductive reactance”.

After explaining an inductor’s behavior the video digs into how a typical inductor coil actually achieves this. The basic idea is that the inductor stores energy in a magnetic field, and it takes some time to charge up or discharge this field, accounting for the delay in current that is seen.

There’s a warning about high voltages which can be seen when power to an inductor is suddenly cut off. Typically a circuit will include snubber circuits or flyback diodes to help manage such effects which can otherwise damage components or lead to electric shock.

[Prof MAD] spends the rest of the video with some math that explains how voltage across an inductor is proportional to the rate of change of current over time (the first derivative of current against time). The inductance can then be defined as a constant of proportionality (L). This is the voltage that appears across a coil when current changes by 1 ampere per second, opposing the change. The unit is the volt-second-per-ampere (VsA^-1) which is known as the Henry, named in honor of the American physicist Joseph Henry.

Inductance can sometimes be put to good use in circuits, but just as often it is unwanted parasitic induction whose effects need to be mitigated, for more info see: Inductance In PCB Layout: The Good, The Bad, And The Fugly.

The Commodore Amiga was famous for its characteristic Say voice, with its robotic enunciation being somewhat emblematic of the 16-bit era. The Commodore VIC-20 had no such capability out of the box, but [Mike] was able to get one talking with a little bit of work.

The project centers around the Adventureland cartridge, created by Scott Adams (but not the one you’re thinking of). It was a simple game that was able to deliver speech with the aid of the Votrax Type and Talk speech synthesizer box. Those aren’t exactly easy to come by, so [Mike] set about creating a modern equivalent. The concept was simple enough. An Arduino would be used to act as a go between the VIC-20’s slow serial port operating at 300 bps and the Speakjet and TTS256 chips which both preferred to talk at 9600 bps. The audio output of the Speakjet is then passed to an LM386 op-amp, set up as an amplifier to drive a small speaker. The lashed-together TTS system basically just reads out the text from the Adventureland game in an incredibly robotic voice. It’s relatively hard to understand and has poor cadence, but it does work – in much the same way as the original Type and Talk setup would have back in the day!

Text to speech tools have come a long way since the 1980s, particularly when it comes to sounding more natural. Video after the break.

[Thanks to Stephen Walters for the tip!]