This project uses a 2.15" e-paper display from Pervasive Display to implement a badge with SD card and Bluetooth LE.The goal is to store images on the SD card or through Bluetooth and upload/manage images via the same Bluetooth link.The badge also includes a micro USB B port for charging a lithium-ion battery (the connector matches batteries available from Adafruit, https://www.adafruit.com/product/1317). The microcontroller is a STM32L071KZU6, a Cortex-M0+, and the design uses it's internal temperature sensor (the e-paper display uses the ambient temperature information to adjust it's refresh cycle).The board is designed to be off most of the time, and powered by the power button, that is also connected to the microcontroller for other purposes. The microcontroller is in charge of cutting the power.
I finally had the time to make some changes to the project. The major difference is the switch to a STM32L071KZU6 MCU, comming in a different package. Other differences are the add of a decoupling capacitor and the 180° rotation of the battery connector. I removed the old files from hackaday, and will put the new ones once I have more time again. The files are available from the CircuitMaker project page.
I already ordered the PCBs, but this time with a ENIG finish and 0.8mm thickness. I'm expecting to get them around mi-January.
After upgrading the microcontroller to the STM32L031F6P6, I realized a very unfortunate fact.
Although the STM32L011F4P6 had the BOOT0 pin shared with the PB9 input, the new chip has only BOOT0 on this pin. Therefore, a press on the power button would not be detected. Although the design can still work with 2 buttons, I would like to have 3 buttons design.
On another note, ST also sells modules that includes both MCU and Bluetooth functionality, and if I can make is simpler that way, I will.
I finally had some time to troubleshoot the programming issue that I was having, and realized that the reason I wasn't able to connect to the chip is because the PCB i was using to hold the pogo pins had a defect and the ground plane was missing somehow....
Jump wire in place and now it works!
I am also planning on upgrading the chip to a STM32L031F6P6, for an increase in SRAM from 2K to 8K. The device should still be able to function with the originally intended chip, but bigger SRAM would allow to have the full display in a buffer in the MCU and allow more complex operations. The chip is pin-to-pin compatible, so there will not be a difference in the PCB design. The increased Flash will also allow the storage of few graphics on the MCU rather than the SD card.
So I received all the components, and used my reflow over (toaster) to solder all of them. Unfortunately some shorts appeared, and in the effort to fix it, I overheated the ePaper connector. Everything works fine except I can't connect the display...
Will get another batch of components and try again later in the month.
I finally received the PCBs! SeeedStudio Fusion service have a descent quality actually, less than $5 for 10 boards, without shipping. Come to think about it, I should probably have ordered an ENIG finish, but this will probably do fine.
I just sent the PCB to be fabricated by Seeedstudio. I also received the stencil today.
I added the BOM as a CSV file. Quick note, all of the component except the microcontroller are available from Digikey. Other websites like Mouser have the microcontroller, but miss other components, although equivalence might be available. The BOM is also available on Octopart at https://octopart.com/bom-tool/qB575L1h.