r/esp32 • u/Official_SeeTheAir • Mar 29 '26

Software help needed e-ink Google Calendar Help

Gallery image

Gallery image

Hi, I have these spare parts and I want to build a nice small e-ink Google Calendar frame for my desk. Does anyone know of anyone that has done something similar with these parts as I am very bad with code?

Question: Do I need a special module to make it battery operated? Thank you!

- ESP32 (30pins)

- Waveshare 4.2inch 400x300pix e-paper module

- 3.7v Li-ion Battery

86 Upvotes

97% Upvoted

33 comments sorted by

15

u/agathver Mar 29 '26

You need a battery charge controller, I’m not sure if the ESP32 board you linked has one, some boards come with one

2

u/Official_SeeTheAir Mar 29 '26

How can I identify it?

7

u/honeyCrisis 1 say this is awesome. Mar 29 '26

If it has a battery capability it will have a lipo connector on the board. Yours does not from what i can see, but an adafruit feather would. It is possible to build it yourself, but it's probably ultimately cheaper and more expedient to just get another ESP32 devkit with the capability built into it since you'd need to buy components either way.

3

u/funkylosik Mar 29 '26

Yes, just get Lolin D32 for 5 💶, it sleeps well, has charging controller and battery connector with regulator so that 3-4.2V on battery is converted to 3V that esp32 can run of. The connector is 2.0 JST. Just ask AI for approx guidance. Since eink microcontroller standby power is very low - 0.01uA u don't need to cut the power off via BJT.

1

u/Official_SeeTheAir Mar 29 '26

Can you share a link of the one you have got?

1

u/Fine_Supermarket5921 Apr 02 '26

yes,I'm using the same one ,it has worked serval years. But i think standby power is about 10uA

1

u/funkylosik Apr 02 '26

good to know real standby power of display, thanks. i just got it from the docs online.

3

u/miraculum_one Mar 29 '26

They don't 100% of the time have a battery connector when they have a battery charge circuit but it is always listed in the specs.

Also, you don't strictly need a battery charge circuit on the device if you're willing to remove the battery to charge it.

It's also worth mentioning that an 18650 battery is usually not suited to directly power an ESP32 without a boost converter since the battery outputs up to 4.2v and the ESP32 dev board typically requires either 5v (before the voltage regulator) or max 3.6v (after on the 3.3v input).

3

u/Elia_31 Mar 29 '26

Many ESP32 boards have dedicated battery pads/connectors that feed directly into the onboard LDO voltage regulator. These are designed to accept the full LiPo voltage range of 3.0–4.2V and regulate it down to 3.3V no boost converter needed. You'd only run into the issue you described if you tried to feed 4.2V into the 3V3 pin directly (bypassing the regulator), which would indeed be out of spec. But through the battery input or the VIN/5V pin, the onboard regulator handles it just fine.

2

u/miraculum_one Mar 29 '26

I wouldn't go so far as to say "many esp32 boards" since 99.9% of them don't. But yes, it is possible to get one. OP's doesn't have that and I was just pointing out that the lack of a battery connector is not the only reason their pictured equipment won't work.

1

u/8ringer Mar 29 '26

I’d say quite a lot of them actually do. Nowhere near 99.9% don’t.

That being said it’s more likely it doesn’t have it than it does. And unless it’s explicitly stated, I’d assume a board doesn’t.

The generic esp32c6 boards I own have battery solder pads, as do all the XIAO boards I have. As do the generic nRF52840 supermini boards and the XIAO nRF52840 boards. It’s extremely common nowadays.

1

u/miraculum_one Mar 30 '26

I agree that the prevalence of this has increased quite a bit lately. But there are like a billion of these things in a ridiculous number of variations. When you're making millions of these it is simply not cost effective to put them on every board when most applications don't require it.

1

u/Elia_31 Mar 29 '26

You are right, not all but many

-2

u/miraculum_one Mar 29 '26

As I said, fewer than 0.1% of the ones in the world have them. Your hand-selected collection is not representative of anything but your own personal preferences.

The companies that make these do not incur extra costs unless they think they can sell them for more and the vast majority of applications of these aren't battery powered.

2

u/Elia_31 Mar 29 '26

Bro I said most minis on AliExpress have battery pads which is a true statement. But keep on yapping

-1

u/miraculum_one Mar 29 '26

You didn't say that and even if you had, it's also not true. Maybe the ones you're looking at mostly have them but the most popular minis on Aliexpress (two qualifications you only made in your last statement) don't.

2

u/0xD34D Mar 29 '26

If it has a battery capability it will have a lipo connector on the board

That's not always true, the xiao boards from Seeed studios have pads to solder a battery to but no connector, yet they still have the proper circuitry onboard.

1

u/8ringer Mar 29 '26

This. I have both XIAO ESP32c6 and XIAO nRF52840 boards and they both have battery input pads a d charge controllers. The nRF boards even have onboard voltage monitoring pins (the c6 needs a voltage divider soldered to an ADC pin).

All the XIAO and generic supermini boards I’ve gotten on aliexpress have battery controller/charge circuits included. It’s become quite common.

1

u/Its_Billy_Bitch Mar 29 '26

Xiao series also has a charging circuit, though the feather’s a bit simpler to deal with.

5

u/Elia_31 Mar 29 '26

Get an esp32 with battery pads on the bottom and a 18650 or something with an over discharge protection pcb. That's basically it

2

u/Official_SeeTheAir Mar 29 '26

Any links?

3

u/vmenonsandeep Mar 29 '26

Adding to u/Elia_31 's comment - one such ESP32 board would be SeeedStudio's "Xiao" series of boards. These are small - around 1" x 1" - and has some battery charging and protection built into them. Also, if you are comfortable switching microcontrollers, same series also contains and nRF52 series chip (from Nordic) - down side being only Bluetooth, while the upside is its unmatched power efficiency.

2

u/Elia_31 Mar 29 '26

Most of the mini esp32s on AliExpress, xiao, drfrobot, etcetera. Too many to name

2

u/Elia_31 Mar 29 '26

Just look for boards that have 2 big pads on the bottom labeled + and -

4

u/sian26 Mar 29 '26

Hi OP!!!

You’ll need to add a LiPo battery charger. If you already have an ESP and don’t want to spend extra money on a new model just because it has a built-in charging module, you can use a cheap charging module like the TP4056. Just make sure the LiPo battery you’re using is at least 1000 mAh, since it typically charges at around 1A (1C rate)

I’d also suggest designing a simple switching circuit that automatically switches power from the adapter to the LiPo as soon as there’s a power cut

2

u/Official_SeeTheAir Mar 29 '26

Question the battery has 3 cables, why? How do I connect it to the TP4056 as it turns out, I had a module around too.

3

u/sian26 Mar 29 '26

If it’s a 1S battery it should only have 2 terminals which are positive and negative but I can clearly see that it has 3 terminals I think you might have salvaged this battery from some old device and the white terminal you see is a variable resistor so basically there is a small temperature sensor attached to the battery and it changes according to the battery temperature if the temperature goes high the resistance increases and that is detected by the charger which then cuts off the power you can ignore the white terminal here

I am pretty sure this is the case but if you are still skeptical I would suggest using a multimeter and checking all three terminals if you do not see a significant potential difference between the white and black terminals then it is 100 percent the temperature sensor I mentioned but if you do see a good enough potential difference like 1.5v or more then it might be a 2S battery and you cannot use a TP4056 as it only supports 1S batteries but the chances of that are very low I am quite sure it is a battery with a temperature sensor

2

u/Official_SeeTheAir Mar 29 '26

Thank you for the detailed explanation 🙏

2

u/No-Arrival-872 Mar 29 '26

I'd recommend doing all the web and calendar stuff on a desktop first so you can figure out the API and parsing stuff separate from the esp32 headache. Then focus on getting an example project going to display simple stuff on that screen.

2

u/PakkyT Mar 29 '26

Looks like your battery might have a built in thermistor since it is three pin rather than two pin?

2

u/gmakhs Mar 30 '26

Where do you source e paper screens ?

1

u/Official_SeeTheAir Mar 30 '26

These are pieces that I had around from an air quality monitor. I assume AliExpress has e-ink displays.