Santek EZ Door Sign

The Santek EZ Door Sign is cordless e-ink display intended to be mounted outside of offices or rooms. It is capable of storing 5 custom images that can be displayed and rotated with the side button.

The 2.9" variant which I obtained has a resolution of 296 x 128 pixels and is capable of displaying black, white, and red.

Serial protocol

Background

Santek provides a Windows based app written in C# that is able to interact with the door signs. My goal is to have some Linux based device that can periodically update these displays (such as the weather or calendar events on an hourly basis). In order to do that, I will need to figure out how exactly this device talks via the USB port.

There are some GitHub projects that try to interface with this device already including https://github.com/m3m0r7/ez-door-sign in PHP and https://github.com/kenichi884/ezsign.py in Python. However, the documentation on the serial protocol is a bit lacking. Fortunately, the protocol doesn't seem too complicated.

Serial configuration

Use 9600 baud. No parity.

The display has to be on. Ensure that the blue LED is lit before trying to talk to it via serial.

Commands and messages

Here are some of the supported commands by the display.

Command Type is 0 if it's a command that's sent to the display. It will be a 1 if it's data that's a response to a command made by the display.

Header	Command Type	Command ID	Data Length	Data	Chksum	Ending	Notes
0xBB	0x00	0x00	0x01	slide (1 byte)	??	0x7E	Redraws the specified slide (0 ~ 4)
0xBB	0x01	0x00	0x01	slide (1 byte)	??	0x7E	Redraw slide response
0xBB	0x00	0x00	0x01	0xFE	0xFF	0x7E	Command next slide
0xBB	0x00	0x00	0x01	0xFF	0x00	0x7E	Command previous slide (called 'up' in C# code)
0xBB	0x00	0x01	0x01	slide (1 byte)		0x7E	Check slide data
0xBB	0x01	0x01	0x01	status (1 byte)		0x7E	Response to the check slide call. Status is one of: 0xFF - Slide is blank or unwritten 0xFE - Slide has data
0xBB	0x00	0x03	0x02	slide-canvas (2 bytes)	??	0x7E	Begin sending data for a specific slide and canvas. All data for the slide must be rewritten as everything is wiped. Data is always 2 bytes long, containing: slide: slide number (0 through 4) canvas: Color canvas (0 or 1)
0xBB	0x01	0x03	0x01	0x01		0x7E	Response to the slide-canvas command.
0xBB	0x00	0x04	0x12	column-bitmap (18 bytes)	??	0x7E	send image bitmap data by column. Data is always 18 bytes long. 2 for column number, 16 for bitmap data. Bitmap data here is based on the canvas setting in order to get that extra bit for color. Column: 2 bytes in decimal. (0 ~ 295) (0x00,0x00 ~ 0x01,0x27) Bitmap: 16 bytes. One bit per pixel makes 128 pixels This is how you can retrieve data for the 296x128 pixel display.
0xBB	0x01	0x04	0x01	0x01		0x7E	did send image row data succeed? Data should be 0x01
0xBB	0x00	0x05	0x04	slide-canvas-column (4 bytes)	??	0x7E	Get image bitmap from display memory. Data is always 4 bytes long. Slide: Slide number (0 through 4) Canvas: Color canvas (0 or 1) Column: 2 bytes. (0 ~ 295) To retrieve the actual color, you have to read both canvas See the response payload below.
0xBB	0x01	0x05	0x12	column-bitmap (24 bytes)	??	0x7E	Bitmap data received from a get command. The response message is always 24 bytes long. There are 18 bytes of payload data and is the same format as the send-image-column command. Column: 2 bytes. (0 ~ 295) Bitmap: 16 bytes. One bit per pixel makes 128 pixels
0xBB		0x06				0x7E	iap model
0xBB	0x00	0x07	0x01	0x00	0x08	0x7E	power off

Writing bitmap information

The display is tri-color and uses 2 bits per pixel to denote color. The 2 bits are written across two separate 'canvases' as part of the write operation. When writing an image:

1. Call the start write command (0x03) and specify the desired slide and 0x00 canvas
2. Write the bitmap with command 0x04. This command operates column by column, from left to right, top to bottom. There should be 128 pixels (as the display is 128 pixels high). Black and red pixels should be 0. White should be 1. (see table below)
3. Call the start write command (0x03) again but this time set canvas to 0x01
4. Write the bitmap again with command 0x04 as in step 2, but this time, set the bitmap to 0 for black and white and 1 for red.

You must write to all addresses. The memory for the slide appears to get wiped when a write is initiaited. Skipping any of the columns for either canvases will cause the image to become corrupt.

If you call the 0x03 begin write command but don't actually write anything, the slide data becomes uninitialized and appears completely red. The check slide command (0x01) also returns 0xFF rather than 0xFE denoting that there is no data at this slide.

	Canvas = 0	Canvas = 1	Color
Pixel bit value	0	0	Black
	1	0	White
	0	1	Red

For entirely black and white only pictures, you still need to write all 0's on the second canvas. Otherwise, the slide is will be rendered completely red. It's likely any unwritten data is erased to 0xFF on the flash.