Typie-Walkie with E-Paper Screen

Everyone knows the talkie-walkie, here is a variant with an e-paper screen.

Thanks to its capacitive touch, the e-paper screen turns into a human-machine interface. The user type the message with the keyboard and then press Send. The message is sent and displayed on the remote screen.

The touch e-paper screens were sampled by Pervasive Displays.

Hardware

The central part of the project is the monochrome 3.70" e-paper 416x240 screen with touch. It is connected to the MCUs through the EXT3-1 and EXT3-Touch interface boards, stacked together.

We need two of them, one for each device.

For simplicity, I took two ESP32 boards, the ESP32-Pico-Kit-v4 and the ESP32-DevKitM-2.

Alas, the pinouts are different and some pins are missing. The documentation, although dramatically better than for the ESP8266, is still unclear.

For example, the ESP32-DevKitM-2 was crashing and rebooting endlessly because the default SPI interface was raising an exception.

The problem was solved by specifying the pins of the SPI interface explicitely.

As a tradeoff, the JTAG signals are no longer available.

Software

The application is the same for the two devices. The management of WiFi and MQTT relies on off-the-shelves libraries on top of the Wiring/Arduino SDK.

For the screen, the Pervasive Displays Library Suite manages all the elements of the interface:

The input keyboard is used to type in the messages (TX);
The Send button sends the messages (TX); and
The output text-box displays the messages received (RX).

The keyboard contains three sets of keys: capital letters, lowercase and symbols.

Additionally, the § key changes the layout, and the « key acts as backspace.

The MQTT broker is provided by Mosquitto. It runs on a PC or a single-board computer like a Raspberry Pi.

However, recent versions of Mosquitto require the prior configuration of the mosquitto.conf file to allow the access from outside the PC where it is running on.

Alternatively, a cloud-based broker like mqtt.eclipse.org, test.mosquitto.org or broker.hivemq.com could be used to manage the MQTT messages.

Conclusion

The e-paper touch-screen is surprisingly responsive when using the keyboard to type a message.

WiFi is not exactly a low-power solution and doesn't match the ultra-low power capabilities of the e-paper technology. A variant uses the low-power LoRa radio instead.

However, this project explores an interesting low-power alternative to standard TFT screens, and shows that e-paper screens can act as input devices as well.