![]() There is no checksum or validation either. Then a set of handlers receive the framing, handle the data buffers, and save the received data over SPI to the SD card. Everything is being pushed from the Android app, so the ESP32 initializes the Bluetooth stack to advertise its file transfer service. The majority of the code implements a set of callbacks for the Bluetooth stack. You will need to create your own for your application. I created UUID values manually for the service, transmit, and receive hooks. These provide the Bluetooth serial support. The important libraries needed for this sketch are part of the above packages. Software drivers and utilities for ESP32 are at:įollow these instructions to install ESP32 support to Arduino IDE on a Mac. I compile and upload this sketch to the ESP32:Įspressif makes software libraries available to build and deploy ESP32 sketches with Arduino IDE. Low quality (cheap) SD cards may need the bus speed to be lower to work. When initializing the SPI bus and SD card I use: SD.begin( 4, SPI, 80000000 ) ![]() Wiring guide to the Reflections project is at Espressif uses this library to deliver Over The Air (OTA) uploads of sketches.ĭon’t expect much from the official ESP32 doc site. I also found the ESP32 software distribution includes esp32/hardware/esp32/libraries/BluetoothSerial/SerialToSerialBTM to bridge between Serial and Bluetooth (SPP). There are best practices to fit a payload exactly into the Bluetooth MTU for best throughput, so adding a few bytes to the header is direct and understood. Framing also allows for retries and error handling during data transport. I read that some firmware updates get pushed to mobile devices using SPP.įor framing I create a small header to label the packets and a checksum to minimize data integrity risks. Some tests I did show SPP is faster with better flow-control. If Meghan Trainer is “all about the bass” then I am about “easy”.īluetooth implements a Serial Profile (SPP) to push raw data with some framing to a device. I found a lot of overhead to implement an OBEX object. For reference I looked at how Apple implements the Bluetooth Transport subclass of the OBEXSession object. One offers an OBEX server on the mobile device and pushes data to the mobile device. These are great for transferring a 20 bytes or less.īluetooth implements a data transfer service called OBEX. Where is the file transfer protocol? I found many examples of small data transfer - for example, transferring the moisture content from a sensor in a potted plant. Getting Bluetooth to work with large dataīluetooth surprised me. While it was tempting to implement the FTP standard protocols over Bluetooth transports, using our own data transfer protocol seemed simpler. Implement a data transfer protocol to validate sent and received data. Implement a command protocol to initiate file send and receive operations. Implement an automation pairing and discovery mechanism. Specifically, do not code the ESP32 side using tools outside of Arduino IDE make/compile system. Make this easy for the average Arduino IDE and ESP32 user to understand. I put this aside as it is complicated to implement. I had another idea to have a Bluetooth session initiate the transfer and fire up Wifi temporarily to move the data. A 2.5 Mbyte file transfers in 32 seconds and a 48 Mbyte file transfers in 13 minutes. Tests show average transfer rates with the solution presented here are 74,381 bytes per second. My application does not require real-time data streaming. ![]() My wrist watch has no easy user input for selecting Wifi networks (using SSID) and entering passwords.įast enough speed for data transfer. I chose tar and GZip as widely used standards to build and compress an archive of binary (for example, Using TAR files in ESP32 with SD applications for easy multiple file transfers) and text (for example, JSON encoded procedural scripting command) files.īluetooth has these advantages over Wifi for this application: I distribute the source code to this project under a GPL version 3 open source license. This is my developer’s journal of the problems that I encountered and the work-arounds I used. The media files are binary and are 1 to 40 MB in size. My goal is to produce a gateway app that the wrist watch (an ESP32 using Bluetooth Classic) uses to get the media files from a Cloud service and store them on an SD card on the ESP32 SPI bus. It seems to me that everyone with the wrist watch will also be carrying an Android or iOS mobile device with Internet service. I am engineering a watch to play home videos of my children on my wrist - my Reflections project.
0 Comments
Leave a Reply. |