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Comment by ptsd_isv | Hacker News Reader

You can negotiate charging with essentially a single resistor. Deciding when to stop / balancing cells etc is the harder problem.

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> You can negotiate charging with essentially a single resistor.

For USB sure.... I'm pretty sure this doesn't charge over USB.

I'm surprised, and you'll be surprised, but this is true!! I gotta start actually looking shit up before saying something....

https://en.wikipedia.org/wiki/SAE_J1772#Signaling

J1772 is significantly more than a single resistor. And, while the signaling is analog, all practical implementations are going to use digital circuitry to generate and detect it.

Well, OP Amps are technically "analog" too.

Well, they could be using vacuum tubes…

Op-amps are absolutely, 100% analog in every sense; there's no need to limit this assertion with the nonstandard adverb "technically". The term "analog" was invented in the first place specifically to describe circuits made out of op-amps rather than "digital" circuits. And, yes, you can totally balance the charge on your cells using op-amps and similar analog circuits. You will probably want some sharp PWM waveforms in the circuit, but PWM isn't all the way to digital.

I would question whether a PWM "technically" counts as digital... It is on and off, sure, but so is a mechanical power switch, which few would describe as digital. "Digital" is more when we get higher level values represented by multiple signals that are on or off (aka bits).

A mechanical power switch can certainly be digital; the Harvard Mark I digital computer was made entirely out of mechanical power switches, actuated by solenoids (so-called "relays"). It depends on how you use it—as you say, by combining multiple different bits, either simultaneously or serially.

I agree that a PWM signal is not really a digital signal, but it's kind of on the edge—for example, https://tinyurl.com/25y54mph is a simulation I designed of a completely analog PWM generator (a simulated LM324 op-amp, five transistors, 13 resistors, and a couple of caps), and several vendors offer better-designed versions of the same thing on an IC, but you can also get a perfectly adequate PWM signal out of a digital GPIO pin, and the PWM peripherals commonly included in microcontrollers are entirely digital.

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