4.26" 800x480 e-ink display long-lasting battery powered device that's fully compatible with TRMNL's BYOD. In other words, TRMNL mini.
I wanted a smaller device that I could use to display simpler plugins/recipes that would work with TRMNL's design system. Recently I've built myself a TRMNL (as well as purchased the BYOD license) using Seeed Xiao OG DIY KIT and I really like using it in my day-to-day.
So I thought to myself - what if I had this... but a bit smaller, to display weather and some simple stats? I started looking for a compatible panel that would somehow work with TRMNL image generation. Found a 4.26" 800x480 panel from Waveshare - exact match when it comes to resolution.
It is a DIY project, so you will have to solder and assemble everything by yourself, this includes 3D printing the case.
Here is a comparison of the fully built device to a "normal sized" TRMNL (7.5") - it's a Seeed TRMNL DIY Kit in a case that I designed:
This repository has a lightly edited TRMNL's firmware in /firmware.
Firmware is currently based on v16.10.0.
Changes:
- Added new ENV
[env:dfrobot_firebeetle2_esp32e] - Added Firebeetle 2 ESP32-3 board pin definition
- Removed static
bb_epaperlibrary, added a2.0.0version that supports the Waveshare 4.26" e-ink panel
- Waveshare 4.26" 800x480 e-ink panel with HAT
- Firebeetle 2 ESP32-E dev board
- Li-Po 3.7V 2000mAh 103450 battery
- 50x34x10 mm - needs to have the same dimensions, otherwise you will have to modify the case
- Micro switch - 6x6x7 mm
- M2 screws + nuts
- M2.5 screws
- Access to 3D Printer
I've used the hat version of this display only because that was available in my country and I didn't want to wait for shipping. I desoldered ripped off the pads while removing the headers.
The device could be a little slimmer if I have went with raw panel + Waveshare's Universal E-Paper Universal e-Paper Raw Panel Driver HAT but I wouldn't have built in mounting screw posts.
Follow the instructions in TRMNL's firmware repo, just make sure you pick the correct env ([env:dfrobot_firebeetle2_esp32e]) when building and flashing it to ESP32.
You can change the pins in the firmware if you want, this is what I consider "default", as in "as is" in the firmware I modified.
PIN_CLK 18 // #ffff00 SCK
PIN_DIN 23 // #1500ff MOSI
PIN_CS 25 // #ffa200
PIN_DC 13 // #00ff15
PIN_RST 14 // #ffffff
PIN_BUSY 26 // #ff00d4
VCC → 3V3
GND → GND
PWR → 3V3LEG 1 4
LEG 2 GND
Additionally 10k resistor from VCC to PIN 4The case was designed by me in Fusion360. I designed it in a similar style of the case I did for my Seeed OG DIY Kit TRMNL.
I've printed the case on Bambu Lab P1S with Bambu Lab Matte PLA Bone White filament.
It has a couple of parts:
- Front
- Display ring
- Midframe
- Back
The back of the case holds the whole assembly in place. The USB-C port of the Firebeetle 2 is accessible from underneath.
All the files for the case are in /case:
.stl.step.f3d
There is also a .3mf with everything set up on plates with Bambu Studio.
I designed a stand for it as well (visible in the pictures), which angles the display nicely for desktop usage. It can be used in two different configurations.
Assembly steps assume everything is soldered and you have confirmed it works. I routed the display cable under the midframe, there is enough clearance for it.
- Insert the display ring into the front of the case
- Screw in the board into the midframe
- Screw in the midframe into the back of the display
- Put the battery in the midframe holder for it and connect it to board
- Insert the button into the back of the case.
- I would recommend using a drop of AC glue to hold it in place.
- Insert the display with midframe into the front of the case, pop it in place
- Put the back of the case in, push it in so it snaps shut
I really like TRMNL devices and what the company and people behind it stand for. They had a really great idea and executed it well. This project wouldn't be possible if they didn't open source their firmware.