Esp8266 advice

#1

I’d like to build a largish number of led lanterns for an event that are WiFi enabled so they can flash, fade, strobe in sync (or in turn)

I’m thinking esp8266 is the way to go, but they need to be cheap, easy to build.

I was thinking of something like these strings

Ideally just adding the esp8266 between the battery and the led string, but then I’m restricted to the basic esp8266 modules - assuming they will fit through the neck of a wine bottle. I think the power supply is 3 coin type cells, so notionally 4.5v which is a bit too high to feed straight to the esp8266, so I’d need a voltage regulator, I assume.

Is this feasible?

Should I go for a bigger form factor controller and jam jars?

Ant thoughts?

#2

I’ve seen the following for the ESP32 platform:
https://hackaday.com/2019/04/28/femtobeacon-is-a-tiny-esp32-coin-shaped-dev-board/,
https://www.tinypico.com/ - with the latter including battery regulation support. You may be able to find much cheaper versions of these from the usual suspects (aliexpress, banggood).

#3

Coin cells may not cut it if your running them in a mesh. With Wi-Fi polling they draw and Ave of 70ma but peaks to maintain stability are 300ma. Even with a chunky cap, they can be flaky.

Look at cheap primary Lithium or cheap lipo as the source.

Courty

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#4

I hadnt thought about current draw. This is going to be more complicated than I thought!

Maybe some old 18650s from a laptop?

Could I go straight to the esp8266 without a regulator?

#5

unlikely. the watchdog on the esp is very very twitchy to any kind of instability in supply.

#6

i use a 3.3v LDO regulator to do exactly that, 18650 -> Reg + big Cap -> ESP

Courty

#7

Hmm. This looks like the way to go.

I don’t really know much about regulators, but isn’t the 3.7v from a lipo a bit close to the 3.3v I need to get out? What kind of regulator should I be looking for? Something with minimal external components so I can avoid too much soldering would be good

#8

Just found out LDO = Low Drop Out so one mystery solved!

Still, specific recommendations appreciated!

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#9

It appears that the WeMos D1 mini has an LDO onboard - specifically a ME6211

So if I solder an 18650 straight to the 5v pin of the D1 mini will that work?

If the 18650 gets over-discharged, will it catch fire? Not sure that’s how I want the evening to end…

There’s a battery shield for the D1 which presumably will take care of the over discharge thing, but it looks like it boosts the battery voltage to 5v and then lets the D1 mini drop it back to 3.3v, which doesn’t seem very efficient. It would give me a charging option, but that’s not much use in this scenario.

#10

A charged lipo is 4.2v, a dead one is ~3.6v !
The ldo means it will keep regulating down to almost the output voltage as it doesn’t require much headroom. They tend to be cooler too.
You can get protected 18650 cells which would be best or, as the power runs down, the ldo will drop out at ~3.4v, this however is not a recommended way to manage the battery.
Unlikely to catch fire but very likely to damage the cell if you over-discharge.

Courty

#11

And the ME6211 will need to be mounted on something before it will give its full current. If not they shutdown as they get warm

#12

You can also get battery charging circuits pretty cheap - £6-7 for 5 on Amazon with prime delivery, or if you don’t mind waiting a bit longer, there’s a seller on banggood that gives you a proper battery holder with a charging circuit already affixed to it

#13

That or literally just use a Poundland powerbank - they’re peculiar in that they don’t shut off when the current draw is “too low” which is perfect for projects like that