How does a color e-Paper show (like purple/black/white/yellow or purple/black/white/gray) work with none backlight? Why do they eat so little energy, and the way do they maintain their picture even after energy is eliminated? These are pure questions once you see an e-Paper show displaying crystal-clear content material with out being lit up! Merely put, an e-Paper show accommodates tens of millions of tiny microcapsules or microcups full of charged particles of various colors—corresponding to black, white, purple, or yellow. When an electrical subject is utilized, the particles transfer inside the capsules, altering their place or orientation to disclose or cover particular colors on the floor.
In distinction, conventional shows like LCD, LED, or OLED depend on backlighting or aspect lighting. Their liquid crystals rotate or block gentle to regulate polarisation, and color filters are used on prime to supply full-colour photos. All of this occurs at a microscopic scale to generate brilliant, vivid visuals. You would say that in an e-Paper, the picture is created by reflecting exterior gentle, whereas in different shows, the picture is created by emitting inside gentle. That’s why in a darkish room, LCD/TFT/OLED shows glow visibly—they emit gentle. However an e-Paper show turns into invisible in darkness because it doesn’t emit gentle in any respect. This lack of a backlight is a key cause for his or her ultra-low energy consumption.
What’s fascinating is that e-Paper shows retain their picture even after energy is reduce off. That’s as a result of the microcapsules don’t reset—they keep of their final electrically pushed state. It’s like drawing on paper: as soon as drawn, the picture stays. It solely turns into invisible when there’s no gentle to mirror off it.
My 4 color 400×168 Pixel paper
Nearly a 12 months in the past, I purchased this 4 color e-Paper show from Robu.in—virtually at a throwaway worth (INR 1150)! The product web page had a pattern code to check the show, but it surely solely labored with that fastened picture. Regardless of a number of makes an attempt, I couldn’t change the picture or get anything to work. There gave the impression to be no correct library obtainable to regulate this show, and it felt like the whole optics have been enchanted by simply that one picture! Just lately, I found two up to date libraries, and by combining them, it’s now potential to regulate the show & many different sort of e-Paper shows in nearly each manner. For graphical output, you’ll must convert your picture right into a bitmap format earlier than rendering it. Within the code I’ve written, I created an analog-digital hybrid clock that additionally shows temperature, relative humidity, and dew level—due to an RTC (Actual-Time Clock) and an AHT10 sensor. As a playful contact, I additionally added a small raspberry picture that randomly seems in numerous positions on the display screen, full of random colors—including a little bit of attraction and life to the show.
Low-Energy Operation
To run it on a battery, we now have switched off all of the pointless options of the ESP32. These codes are defined beneath.
WiFi.mode(WIFI_OFF); //As we’re not utilizing WiFi
btStop(); // disables Bluetooth
Serial.start(115200);
delay(50); // small delay if wanted
setCpuFrequencyMhz(40); // Scale back CPU frequency for low energy consumption
Wire.start(SDA_PIN, SCL_PIN);
Wire.setClock(100000); // Decrease I2C clock velocity for low energy
Serial.finish(); //Could causes the change on of the Onboard LED; if not, this may cut back energy
//consumption additional; simply strive & see
esp_sleep_enable_timer_wakeup(1 * 60 * 1000000); //Sleep for one minute
esp_sleep_pd_config(ESP_PD_DOMAIN_RTC_PERIPH, ESP_PD_OPTION_OFF);
// Flip off ADC & different RTC peripherals to additional cut back energy consumption
esp_deep_sleep_start();
} //setup ends.
Since we’re utilizing deep sleep, something inside loop() will ultimately be bypassed. Nonetheless, earlier than utilizing deep sleep into your remaining code, you could examine how your code works out inside loop() and that’s why if you happen to bypass deep sleep code, your loop cycle will play out usually.
Prototype
How a lot Low Energy
Within the setup proven, I’m utilizing a 3.7V 600 mAh Li-Ion battery. The machine follows a sleep-wake cycle: it wakes up as soon as each minute, updates the show, after which returns to deep sleep. Through the energetic section (about 3–4 seconds), the machine attracts round 6000–7000 µA, whereas in sleep mode, the present drops to 30 µA. Based mostly on this obligation cycle, the battery can simply last as long as two months on a single cost! In case you enhance the time period the battery life will enhance additional proportionately. Test the video right here for energy cycle consumptions.
BOM
- 400×168 3” 4-colour E-paper with HAT: ₹2331
- ESP32 – 01: ₹500
- AHT10 – 01: ₹100
- Regulator SL7533 – 01: ₹7
- DS3231: ₹150
- PCB, Li-Ion cell, Wirings – further
Movies of the Mission
Factors to contemplate
Right GPIO pin connections are important for the show to work correctly. Whereas the I²C pins could be reassigned from the obtainable GPIOs, the code should be up to date accordingly. I’ve used just one aspect of the ESP32, so my pin picks mirror that constraint.
To assist with GPIO configuration throughout completely different boards, the file GxEPD2_wiring_examples.h is included in the primary code and gives reference pin mappings for quite a lot of supported boards.
Schematics
Because the machine is a low-power 3.3 volt machine and we intend to run it from a battery, we now have used a low-dropout 3.3 volt regulator named 7533 as an alternative of the favored 1117, which has a bigger dropout voltage. The sensors are 3.3 volt low-power sensors.
Software program
The libraries which can be important for this challenge can be found within the hyperlinks beneath.
Obtain these two zip recordsdata after which add them into your Arduino IDE [Sketch -> Add Library -> Add .zip Library… ]
Since they’re massive, they could not get put in into your …/library folder. In that case copy these .zip recordsdata into your ../library folder after which do the method once more. If all fails simply extract the .zip recordsdata after which copy these whole folders into the ../library folder.
Different important libraries: RTClib.h and Adafruit_AHTX0.h could also be put in utilizing Sketch -> Add Library -> Handle Libraries…
After doing all these run this challenge sketch and it’ll run. The sketch consists of 4 recordsdata –
- GxEPD_wiring_examples.h – You’re going to get board-specific wiring particulars
- GxEPD_selection_check.h – That is the E-paper-specific variables
- GxEPD2_display_selection_new_style.h – E-paper particular embrace recordsdata to course of
- GxEPD2_U8G2_epaper.ino – Most important challenge sketch file
All these recordsdata have been hooked up as a *.zip file.
Allied different makes use of of this challenge: Other than the day-date-desk-calendar-temp-humidity show that we now have achieved on this challenge, there are different potential makes use of potential on this challenge.
- Low energy desktop climate station: Climate station with AHT10 / BME10 & icons of cloud, rain, solar, moon, section and so on. The climate report could also be obtained utilizing the Web.
- A To-do reminder in your desktop: Show day by day to-do listing. The file could also be fetched utilizing electronic mail, Intranet and so on. & displayed with an alarm sound. You will have to make use of an I2S amplifier for taking part in out sound.
- A Plant monitor / show: Will show moisture degree, plant title, gentle publicity and watering reminder. Being an E-paper the battery life will likely be very lengthy.
- A Customer counter: Displaying occupancy earlier than a gathering room lab entrance and so on.
- A customer batch: Displaying title, Designation, objective, room and so on., displaying the QR code.
- Grocery store tag or shelf degree: Displaying title, merchandise code, charge, QR code and so on.
Obtain Supply Folder
Aftermath
E-paper is poised to develop into a mainstream show know-how within the coming decade as a result of its ultra-low energy consumption and wonderful daylight readability. Whereas its refresh charge presently lags behind LCDs or OLEDs, developments are steadily closing this hole. The arrival of 7-colour E-paper marks a major leap towards extra vivid and informative visuals. With evolving controller assist and higher libraries, DIY and industrial adoption is certain to develop. This challenge is only a small glimpse into that promising future.
