Prelude [Pros & cones]

I was simply fascinated by the bright colors of e-paper that are displayed even when the power supply is removed which is true for both black & white & color e-papers. The view angle of e-paper is 180 degree which is an extra advantage and they have no backlight and they reflect the same ambient that are incident on them. This results in extremely low power consumption for e-papers. I purchased a few e-papers even without knowing how to deploy them. One among my stock was a 7.5” black & white e-paper. One significant disadvantage of e-paper is that their refresh rate is not fast rather very slow – 3 seconds to 8 seconds. This is the main reason the e-papers have not yet entered in to the mobile screen area. They are mostly limited to e-readers and clock displays having only hour & minute displays. 

The project 

This project is built on a 7.5” black & white e-paper [800X480 pixel area] a clock having a analog clock view with second hand display.Sure the second hand cannot move every second but in every 2 seconds and sometimes in 3 seconds the hand display works. The entire circuit takes about 60 milli ampere on a 3.7 volt LiPo / Lion cell and runs for two+ days non stop. In the event of power failure the one-cell back up will be more than enough!
 

BOM

(Items | Price / Source)

• ESP32 – MCU  | INR:550 / USD$ 7 / robu.in, aliexpress.com, amazon.in
• HT7333A – 3.3V regulator | INR:30 / USD$1 / amazon.in
• 7.5” E-paper Black & White | INR:4799/USD$60/ amazon.in, robu.in, electronicscomp.com
• Wires, PCB, connector | Robu.in, amazon.in, aliexpress.com
• Cap 10MFD | INR:10 / amazon.in

Tricks & testing

Unlike in a normal Arduino programming what you put inside the loop {}, it keeps repeating, in e-paper programming you cannot repeat everything to have e-paper work. E-paper has display divided into two pages – firstPage and nextPage. You have to write in both the pages in reverse color so that when firstPage expires and nextPage starts the reverse colors will cancel each other and you will get your figures display properly. In the first page if you write white on black border in the next page you have to write the same figure [or text] with black on white border. If this is not followed you will have a flickering ghost image changing continuously! This is trick we used to have the display changing successfully every second inside the loop. For 3.3 volt we have used low power, low drop rate HT7333A voltage regulator. It’s quiescent current is 4 micro ampere. The input voltage is 12V to 3.47V such that when the input voltage reduces to 3.47V you still would be getting 3.3V for running the circuit.

Project Schematic

Project prototype

Connection Details

In the connection HAT ensure that the SPI connection switch is towards – ‘4 wire’ SPI side and the display config switch is towards ‘B’ side otherwise the display may not work! The ribbon cable between the e-paper & the HAT is very delicate. Try not to move this cable much else it may damage the e-paper permanently!

Video link

 https://youtu.be/nD0xoOV_DkY

Software

The total software is attached herewith. The library files are to be installed in the libraries directory of Arduino. The sketch file is to be placed in Arduino sketch directory. For easy understanding or in case your e-paper is of different make [other than waveshare] I have retained the commented out lines of the sketch so that if required one can uncomment & change the right display driver. The power consumption of the clock is about 60 milli ampere on 3.7 Volt cell. On a very old (18650) LiPo cell the clock runs nonstop for 2.5 days. The clock best fit for solar driven hall clock / street clock / park clock where a couple of days non availability of sun shine will not stop the operations. The e-paper viewing angle is 180 degree and can be visible under broad daylight. However, during dark night or in absence of light E-paper will not be visible. It needs incident light to work, e-paper does not have any light! In case a solar panel is used then the charging module needs to be connected which is not provided in the schematic.

Aftermoth

E-paper is evolving continuously. Days are not far when the e-papers will replace the present oled screens of the mobiles and other handheld devices resulting in huge reductions in the power consumptions of these gadgets thus increasing their usage time.