The Tech Blog

Memory LCDs have been around for a while. It came into my radar only recently. I thought it deserved an dedicated explainer. It sits right in the middle of a TFT LCD and e-paper. Let’s discuss that today.

A Memory-in-Pixel LCD is still an LCD, but each pixel contains a small memory circuit. In Sharp’s panels, its 1 bit/pixel. Once written, unchanged pixels do not need the same image streamed continuously. The panel is reflective too, so daylight replaces the backlight used by most TFTs.

Its really power efficient. Sharp’s 1.28-inch, 128 × 128 LS013B7DH03 specifies about 1µW typical while holding an unchanged image and 50µW when updating the full screen once per second. A similar 1.3-inch TFT module can use around 90mW just for its backlight. E-paper can approach zero between updates, but a typical 1.54-inch B/W panel uses about 26.4mW while refreshing and takes around 2s for a full refresh. Hence it kinda sits in middle.

You also get excellent sunlight readability like e-paper, but much faster response for changing numbers, menus, graphs and simple animation. Indoors it is less vivid than a backlit TFT, and panels are usually monochrome or some limited-colour.

The interface works well with small MCUs. A 128×128 monochrome frame buffer is only 2kB. Sharp’s panel uses a simple 3-wire serial interface, and you can rewrite only the lines that changed instead of pushing the entire frame.

There is one important difference from e-paper. The LCD still needs a tiny amount of power and periodic VCOM polarity inversion, so it cannot retain the image indefinitely after power is removed.

I think its sweet spot is an always-on battery device where the screen changes often, such as watches, meters and outdoor instruments. If the image changes once an hour, e-paper is hard to beat. If it changes every second and battery life matters, Memory LCD becomes very interesting. Cost remains a constraint. These panels are generally above commodity TFTs and closer to small e-paper modules. Do check them out for your future requirements.

The protest in Jantar Mantar, Delhi, ended after Education Minister resigned. But internet shutdowns during the protest, followed by a Govt direction asking GitHub to remove opensource BitChat, concern me as a technologist. Privacy is a fundamental right in India, and personal communication cannot be held hostage to the whims of Govts. Alternate decentralized routes exist, I want to talk about that today.

When mobile data is blocked, your phone still has Bluetooth and Wi-Fi. BitChat uses Bluetooth Low Energy to discover nearby phones. Each phone relays packets, so a message can cross several people without towers or a central server. It works best in a dense crowd. Encrypted messages can be stored temporarily on nearby phones and delivered when one later encounters the recipient.

A local Wi-Fi network is another option for a confined site. A RPi Zero 2W can act as both an access point and a local chat server. Even a normal home router can provide the network while phone apps exchange messages directly between connected devices. Several battery-powered portable nodes can widen coverage, but they need a Wi-Fi mesh backhaul that synchronizes messages between them.

For longer range, an engineering option is Meshtastic. Your phone connects over Bluetooth to a LoRa radio, while those radios relay short packets across a wider area. It works well for text, location and coordination. However, every person in the network needs extra hardware, making it harder to deploy spontaneously, and LoRa has too little bandwidth for images or video.

These systems provide local messaging, not internet access. They reach the wider internet only when one node has an external connection. A jammer aimed only at cellular bands would leave Bluetooth, Wi-Fi or LoRa working unless its super wideband(highly unlikely).

Any tool/tech can be misused. That is true of phones, cash and encryption too. That does not justify banning it. When the Govt blocks private communication because it cannot monitor every message, it is actively pursuing surveillance power. The protest may be over, but the precedent remains. Hope this doesn’t repeat again.