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Comment by londons_explore | Hacker News Reader

This circuit is awfully complex.... it's possible to do the same with a far simpler circuit if you use the same coil for sensing and accelerating the ball.

A small microcontroller could do both - perhaps even with low enough power that the whole circuit could stay turned on for years on a charge (when not flinging the ball).

Looking at the total energy you need to impart on the ball, you should be able to do that with a far smaller coil and many fewer capacitors as long as you have a suitably shaped steel core to keep the flux path low. I suspect you might be able to do it with no capacitors at all, since modern lithium cells are perfectly happy to deliver 100 amps for a few milliseconds.

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> This circuit is awfully complex ... A small microcontroller could do both

Adding a microcontroller might reduce the number of components used, but it's a bit disingenuous to claim the result is "simpler".

I think you could drop coil sensing of the ball entirely and simply switch the electromagnet using the metal ball contacting the two metal rails. A dialectic gap in the rails near the bottom of the track could turn the electromagnet off at the right moment.

You say that the circuit is complex, but it's the other way around.

Its simplicity is the cause of the high component count.

An entire microcontroller to run an approx 3-line program?

Cheaper than to have a microcontroller that results in a smaller PCB vs discrete components that make the PCB bigger.

Using a single coil, the microcontroller program is pretty complicated. It needs to pulse the coil very briefly on a regular basis and measure the resonant frequency.

If you do the capacitor-less design, you might want to have a steel core with sawtooth top, and then use software to measure the position of the ball relative to each tooth and turn the coil on while the ball is heading towards a tooth and off when the ball is heading away. That allows the energy to be extracted from the battery slower.

You might also choose to have your coil driven by an h-bridge. That means you can put the energy from the magnetic field that builds up in the steel core back into the battery between each 'tooth'. That should dramatically increase energy efficiency, allowing you to use a smaller (cheaper, lighter, more eco friendly) cell or have the battery last longer. To do that, you'll need current sensing too.

That's very common. Look at all the $0.03 microcontrollers on LCSC. They save time, money, and board space.

Throw in a node.js implementation with 100 dependencies and we're cooking, simple as.

I'd like to see the videos of your version!

Railgun instead.

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