The intention was to not need a custom PCB for this project. While it could surely be consolidated and simplified, the building block nature makes it easier to see how the components interact and can be easily expanded or reused.
- Adafruit #3405 - HUZZAH32 - ESP32 Feather Board
- Adafruit #4098 - 2.7" Tri-Color ePaper Display
- Adafruit #3582 - Pimoroni Button SHIM
- Adafruit #2750 - LiPo Battery 3.7v 350mAh
- Amazon - Micro Slide Switch
- Amazon - Magnetic Name Badge Holder
The ePaper display has a resolution of 264x176 and is essentially two 1-bit displays layered atop one another. Each byte can thus store 8 pixels and there are two buffers, one for black/white and one for red/white. That means 264*176*2/8=11,616 bytes of RAM are required to hold the display buffer.
And ESP32 was chosen over a lower-powered chip for several reasons. Having the frame buffer in native RAM makes it very easy to manipulate. The higher clock speed means drawing operations don't take much time for even complex screens. Onboard WiFi and BTLE give additional options for future expansion -- a customizer phone app, displays with live data, etc.
This particular ePaper module has an onboard SRAM that makes it usable with low memory devices. It's not needed in the current project state, but it's definitely usable if memory becomes constrained.
There's also a MicroSD interface, which could allow for easily-updated image files, optional fonts, and icon sets.
With no special precautions beyond sleeping and polling for button presses every half second or so the battery should last at least a day or two. Deeper sleep and using interrupts instead of polling could extend that significantly. Startup is almost instant though, so only turning the device on when a display update is desired would save the most power.
The slide switch and magnetic badge holder are generic parts that can be swapped for whatever. For the case as designed, the switch needs a 15mm mounting hole spacing and the body is 10 x 5 x 5mm. The badge holder base plate is approximately 45 x 13mm and the case recess is just to make alignment easy.
A case suitable for 3D Printing is available in the stl folder. Editable STEP files are also provided.
The case consists of two parts:
The front case is designed to hold all of the components. The plastic pin patterns are intentionally slightly larger than the component hole spacings to allow for a slight amount of tension during test fitting. Once everything is tested out, the extra protruding length can be melted with a soldering iron to "heat stake" the parts to prevent vibration.
The back case is designed to snap securely into the front case. It features a recess for the badge holder base plate and print-in-place compliant button mechanisms. This is designed with ~0.4mm nozzles (0.4-0.5 line width) and 0.2mm layer heights in mind, but will probably work beyond that range some. Likewise, a material that can take some elongation before failure, such as PETG, will be more readily successful.
A detailed view of the compliant button shows how it was designed with a thin, long element supporting the button to prevent rotation and removal, but allowing enough flex to click the microswitches beneath.
The wiring diagram here represents the pins connected as they are currently laid out in the code. Other pinouts are possible with adjustments. Wiring was done with two short lengths of ribbon cable (hence the sequential colors), keeping in mind the intended final layout shown below.
This project uses the PlatformIO IDE to handle the installation of toolchains and packages needed to compile the ESP32-targeted code. PlatformIO IDE is built on top of VSCode so that will be installed first.
- Follow the instructions from PlatformIO about VSCode & PlatformIO IDE Installation.
- Download the latest copy of the code here by using the green Code Download button above the file list. You can download and extract the ZIP file, or if you are used to source control can clone the git repository.
- Back in VSCode with PlatformIO IDE installed, click the "alien head" icon on the left sidebar, use the Open button under PIO Home, then click the Open Project button on the tab that opens. Navigate to whatever folder you extracted the files into and open the project.
- PlatformIO should then automatically install the platform files needed to compile the code. This will take a couple of minutes to download and process. Eventually in the "alien head" icon, the top section will change to Project Tasks. Click Build and make sure the software compiles successfully. This'll probably take a couple of minutes this first time, as there are a lot of background libraries that only get built once.
- Once everything is working, plug in the board with a Micro USB cable, then click the Upload and Monitor task button. This will send the code over to the badge, then start the program. The monitor window will also appear showing log messages output by the various ESP_LOG lines throughout the code, which let you see what is happening when. Now that the code is installed and working, the badge can be unplugged and the code will be retained and can now be run from the battery.
The standard mode has up to 5 static pages assigned to the 5 buttons. Mounted in the case as provided here, the A button is the one on the right when looking at the back case, then B through E proceeding left. Turn the badge on, then press one of the buttons to display that image. As written, the badge sleeps and checks for button input periodically, so holding the button for a slight amount of time may be required.
A secondary mode has been added that showcases some potential advanced capability. To use these secondary modes, hold down a button while turning the badge on. If the A button is held down during power on, a WiFi access point mode is started. Connect to the access point using the following details (or whatever you configured in include/hello_config.h):
- SSID: HelloBadgeXXXX (where XXXX are the last 4 hex digits of the board's MAC address to allow several to coexist)
- Password: t0mat03s
- Mode: WPA2 PSK
In this WiFi mode, your device will be assigned the IP Address 192.168.4.2. Open a web browser and navigate to http://192.168.4.1/ and an interface will appear. Using this interface, you can upload an image, adjust thresholds, see a preview of the black/white and red/white layers, then send it to the device for display. At the bottom is a choice of slots B through E. Choosing one of these slots will store the final uploaded image to flash for future display. Access these images by holding down the button corresponding to the slot while turning the power on.