Specs
- TI CC1110 - 26Mhz 8051 32kB Flash / 4kB RAM
- 6.4 x 3.5 in ePaper display (BWR or BWY) 640x384px
- UC8159 like EPD controller supports 3 bits per pixel
- 1 Mbyte SPI flash, 10 image slots
- 6x CR2450 button cell
- SubGhz (868 Mhz / 915 Mhz) Radio
- FCC ID: VC7120-0157
Programming
See Flashing CC1110 Based Chroma tags for information on how to flash custom firmware onto the Chroma74.
Refer to ATC1441's and bimmi's pictures for test point locations.
Opening Chroma 74
One way to open the TAG is to gently pry the base away from the bezel using a small flat screwdriver or spundger starting in the middle of a long size and then moving towards a corner.
Once the bezel is removed place the tag screen size down on a table and then release the two tabs between the cells next to the label.
The back should now pull off easily.
All of the test points are on the top side of the PCB so there's no need to remove the board from the plastic separator.
Chroma74 Programming Jig
Discord user bimmi designed a handy programming jig for the Chroma74 which is particularly helpful if you have more than one that you want to flash.
Compatibility
There is only one KNOWN version of the Chroma74, if you have one with a PCB labeled as something other than "EDK293 Issue 2" please let us know.
To Do List
This list is in no particular order.
- Modify code to use original LUT data from SPI flash (to support temperature compensation)
- Add slide show support
- Add support for gray scale images (black + 5 shades of gray + white + red/yellow). This also requires AP firmware modifications.
- Add button support (3 GPIOs are available on test points)
- Add custom LUT table support
Effort is spent on items on the "To Do" list based on available flash and RAM space as well as developer motivation.
If something important to you is on the list please make your desires known!
History
This was one of the tags reverse engineered by Dmitry Grinberg who's code is the basis of the OpenEPaperLink project.
This tag has been somewhat readily available for some time and multiple DIY projects have used it successfully.
At the moment (March 2024) the tag is still available from multiple vendors on ebay.
Several of the ads have been active for several months and ads with higher asking prices for multiple years.
Even the higher priced units aren't completely outrageous ($44) but are close to the price of a new display from Waveshare.
This tag is no longer in production, it was replaced by the Chroma 74 H+ which has a higher resolution screen and a more modern SOC. From outward appearances the Chroma 74 and Chroma 74 H+ are identical.
Battery Current
| Mode | Average | Peak | Notes |
|---|---|---|---|
| Deep sleep | .74 microamps | ||
| Sleeping | 1.2 microamps | ||
| Only CPU running | 4.2 milliamps | ||
| CPU running SubGhz rx |
28.0 milliamps | ||
| CPU running SubGhz Tx |
36.8 milliamps | Full power | |
| Display update | 15.3 milliamps | 94.4 milliamps | Probably depends on the image being drawn |
This PPK2 screen shot captures the Chroma74 waking up, downloading an image update and displaying it on the screen.
SPI Flash Memory Map
EEPROM size: 0x10.0000 / 1024k / 1 Megabyte.
Image size: (640 x 384 x 3 bits/pixel) / 8 bit / byte = 92160 bytes, rounded up to erase boundary = 94,208 / 0x1.7000.
| Start Adr | End Adr | Size | Usage |
|---|---|---|---|
| 0x0.0000 | 0x0.1fff | 8k | Factory NVRAM |
| 0x0.2000 | 0x0.5fff | 16k | Factory LUT ??? |
| 0x0.6000 | 0x0.dfff | 36k | unused ??? |
| 0x0.e000 | 0x0.ffff | 4k | OEPL Settings |
| 0x1.0000 | 0x1.8fff | 36k | OTA FW update |
| 0x1.9000 | 0x4.6fff | 92k | Image slot 0 |
| 0x4.7000 | 0x5.dfff | 92k | Image slot 1 |
| 0x5.e000 | 0x7.4fff | 92k | Image slot 2 |
| 0x7.5000 | 0x8.bfff | 92k | Image slot 3 |
| 0x8.c000 | 0xa.2fff | 92k | Image slot 4 |
| 0xa.3000 | 0xb.bfff | 92k | Image slot 5 |
| 0xb.a000 | 0xe.7fff | 92k | Image slot 6 |
| 0xe.8000 | 0xd.0fff | 92k | Image slot 7 |
| 0xd.1000 | 0xe.7fff | 92k | Image slot 8 |
| 0xe.8000 | 0xf.efff | 92k | Image slot 9 |
| 0xf.f000 | 0xf.ffff | 4k | unused |