• Almost done gathering components

    Ines Wisseme • 12 小時前 • 0 comments

    I am almost ready to start on this project. While researching how I would implement it, I have done some discoveries that have changed my outlook, and now I need to buy a few more components. I will update the list of components to buy once I am sure of everything. Here is a more detailed reasoning behind my change of mind:

    1)  E-reader: Kindles are popular in the electronic community, so much that you now have dev kit/breakout boards designed and sold by companies to help integrate them directly to your pi/pico board.

    However, less known brands or discontinued models do not have that support. That is the case with the e-reader I bought (sony prs-700, I couldn't find a kindle I liked). I don't have the knowledge to crack the firmware on the e-reader, and it would be useless anyway since it won't be applicable to other brands, so I am choosing another path.

    Instead of directly interfacing the pico to the screen, I will attempt to simply use the already present firmware to my advantage: most e-readers have their own local memory cache, but they will load the epub from an SDcard.

    My plan is to trick the reader into reading a fake epub/pdf file that can be overridden by the pico. For that I need to figure out a few things about my own e-reader behavior. Once the SD card is read by the e-reader, does it loads something on its own memory or is it only for the OS uses? What happens if the SDcard is disconnected and re-connected? What happens when I turn a page, does it reload the data from the SDcard or pre-load a few pages in advance? 

    If the e-reader loads each pages one-by-one from the SDcard, it would be easier to trick it into turning to an empty page, then going back to our previous (now updated by the pico) page. I am betting on my e-reader being an older model, but I am not sure it would even work on newer models which uses other means of storage. It could even be a brand-by-brand case.

    2) Battery: Currently my e-reader is powered by a Li-po 1100 mAh 3.7V battery, and the pico zero w 2 takes 5V. My plan is to have the battery power both devices for a comfortable user experience, using a power split, but I need to consider their power usage and I am limited by the size of the current battery. I could go with a bigger battery, however it would mean that I now also need to design and print a e-reader frame with space to accommodate it, plus the pico. It's not impossible, but if I can avoid it I will as I am on a time limit. 

    Most likely I will swap it for a 2000-3000 mAh battery and implement idle/sleep mode to save on power. 

    3) File Update: For this project I am not looking to support images, though I assume it is possible as the e-reader reads multiple file format. My goal is only to display updated text. 

    For this, I will most likely create a HTTP server, as I have previously mentioned. One point to consider when moving forward: how permissive is the firmware with foreign files. Here I am assuming most e-readers only accept e-pub with the proper signature (meaning you bought them from a trusted source), and need to be jail-breaked to accept foreign files. Once again, it's something I would like to avoid, but most likely won't be able to.

    Now that I am working on a prs-700 and not a kindle, I will update the name of the project to reflect that.