Converting 8VAC to 5VDC

Other Hardware General Electronics
21

sshaikh:
I've since settled on using a "5v USB charger" solution.

Well, the 8 V AC and that buck converter with its included capacitors should have done the job.

sshaikh:
I'm considering using a micro USB breakout board (like this) to get the 5v out, but I'm a bit puzzled as to how to feed this into the board without having to go back through its USB port.

Schematic is here

All just a waste of time. The micro USB breakout functionality is already on your board.

sshaikh:
I could use a microusb plug (like this) or (maybe inadvisable?) stick a wire on the USB socket on the board (like this?)

Very inadvisable! I cannot imagine from where you dredged that last link, but it appears to be some sort of total nonsense! There is no problem. Pin 15 clearly is the USB power pin, 5 V, so either you feed your regulated 5 V into pin 15 or you plug your USB charger into the micro USB jack and take your 5 V power for other devices from pin 15. No contest.

sshaikh:
but I was wondering what the the VIN label on the Power schematic was for (I can't see it anywhere else).

Neither can I. It is the power rail for that part of the circuit - the ESP32 itself - that is fed via the regulator - and then battery-backed-up. I would have thought it might go to pin 16 of the CH340 but perhaps the design was changed at some time. The only slightly unfortunate part is that the CH340 is powered by the battery backup.

sshaikh:
On the other hand, I notice from the same schematic that VBUS terminates at the pin 15 (USB) - would it be safe to power the rest of the system (essentially two relays) from this pin instead?

That is exactly what it is for. It should have been labelled "5 V" like the D1 Mini to avoid confusion.

22

Thanks Paul. You're right, it's no contest. I'll go with that!

23

Paul__B:
Bad idea. Very bad. If you are referring to the switchmode design shown, such regulators are non-trivial to construct and operate stably - and you do not want it to misbehave in any fashion.

I think it important to but Bad in context, here. Probably a bad idea to expect to produce a result anyone should rely on. But, as an instructional adventure, this could be a Good idea. Just go into it with the understanding you will likely fail -- many times. But, that's how we learn, right? After all, isn't that what "Lab Period" is all about?
But, this could, also, be considered a Bad idea for these reasons:

  • If you discourage easily, this will kick your butt -- best avoid.
  • If you are short on funds -- i.e. can't afford to shell out $$$ for the proper tools, for many PCB iterations, and parts purchased in quantity -- then best avoid.
  • If you don't like smoke -- or have no viable way to properly ventilate a space [probably not a good idea to breath too much of that stuff], or if your acrid smoke will piss off the wrong people -- then best avoid.
  • If fire hazard is a game changer -- then best avoid.

BUT, who knows, you might get lucky -- after all, we are making an assumption of incompetence :wink:

24

ReverseEMF:
BUT, who knows, you might get lucky -- after all, we are making an assumption of incompetence :wink:

Karma to that :grinning: reply.

No, it's not incompetence, it would merely be very bad tactical judgement to re-invent the wheel.