Simple Flexible watch based on stm8l151f3 and EPW1404AA1 flexible display.

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Simple Flexible watch based on STM8L151F3 and EPW1404AA1 flexible display made by Futaba. This project is inspired from and my previous failed project FlexWatch (based on GDEW0102I3F flexible E paper ; Revive this project soon).

This project is about making the nicey watch out of Flexible OLED made by Futaba. This is the earlier (yet cheaper)  version of current Flexible display in Futaba's line up. I got this of an Aliexpress for roughly 15 bucks-ish. In fact, this is the only place that you can get the Futaba Flex OLED (beside Alibaba, which is the same company on Aliexpress). Event other main distributors like M0us3r, D1g1k3y, RS C0mp0n3nt don't have the newer Flex OLED on the shelf. 

The brain of this project is my go to choice MCU. It's STM8L151F3. Only 1K of SRAM but this display framebuffer is only 256 Bytes CRAZY! (as I always play with >1Kbytes buffer Display). 
Nice Thing about this MCU is the built-in RTC with low power mode. Without requiring any external Oscillator XTAL. Though the time keeping my not precise. But It's cool watch so acceptable xD.

However, I have 2 major concerns, 

The first, (some part of) display itself is really fragile. Normally the display will sit on some sort of fabric-like thingy that wrap around my wrist (first prototype is gonna be crappy made D.I.Y Velcro wrist band). Bend radius isn't big problem for this though. But there's a SSD1316 die that really fragile, I can prevent this region not to flex with some rigid plastic supporting underneath. 

The second one is battery (physical shape, capacity, max discharge current and low power design), 

Juice Sucking when sleep: when deep sleep I estimated the juice sucking to be around (at most) 30uA. That's 10uA from STM8L in Active halt at worst case scenario, normally (according to datasheet) should be right around 2-3uA. And the LTC3459 (boost IC for supplying Positive bias voltage to OLED) sleep current according to datasheet is between .1 to 1uA, my guessing is probably around .2-.5uA. The Display itself according to datasheet is around 1 to 10uA so gonna guess that it's ~ 5uA.

I need to take other factors into an account for example parasitic resistance, Imperfection of silicon chip that might deviate from "normal" operation current usage and more that I can't even thing of.

Juice Sucking when running: In running mode, I estimate that it will running about 20mA, STM8L at around 4-4.5mA, Display at 15mA including LTC3456 current consumption. this would be problem when comes to battery max discharge current which is proportional to the battery size. 

Batter Size Shape Capacity and Maximum discharge current: finding the battery to suit this project is really hard. I've spending time about 1 month now and still haven't found the good candidate for powering this project yet. I added the LIR2032 into the list since it's capacity, size, and max discharge current is kinda suitable for this project. but still, there's more smaller size battery out there that might suit for this project as well. I'm looking at the wireless earbud / Airpods battery too. but these are too expensive compare to LIR2032. 


Display Datasheet, Also some commands are referring to the SSD1316 datasheet as well.

Adobe Portable Document Format - 1.25 MB - 09/14/2021 at 04:46


  • 2 × 1uF 0603 16v
  • 2 × 2.2uF 0603 16v
  • 2 × 10uF 0805 16v
  • 1 × FH35C-11S-0.3SHW This is Hirose 0.3mm pitch FPC connector, 11 pins.
  • 1 × 33uH 1210 Inductor for out 10v OLED bias boost IC.

View all 15 components

  • Rev4.0 PCBs are here!

    TinLethax12/16/2021 at 10:44 0 comments

    OSHpark mail package showed up today. It's long waiting rev4.0 Fl3xWatchOLED PCBs. Last time sadly no sticker came with pcbs, so I contacted OSHPark and they kindly includes tons of them. Anyway, here's some pics of them.

  • We got good n bad news

    TinLethax11/08/2021 at 16:12 0 comments

    I've tested the circuit. Good news is the 10 volt boost circuit work pretty well, all electrical characters met what I wanted. Sadly the bad news is the connector seems to be happy with faced down FPC. which it's means that I need to use the connector in reversed connection. Thus the display will now facing down. To reverse this, I need to put the FPC on another side of PCB, so the display can face up toward us but face down relative to the connector. Another PCB rev, Another PCB batch. Another 2 months 😥

  • PCBs arrived!

    TinLethax11/08/2021 at 10:06 0 comments

    after long months of waiting. Flex PCBs finally arrived from @oshpark all the way to Thailand. And here the PCBs

    (sadly I didn't get the sticker along with these 😭)

  • I ordered the PCBs and components!

    TinLethax09/30/2021 at 10:06 0 comments

    Very very soon (probably next 2 weeks). I will receive the rev 3.1 flex board from OSHpark and probably next month I will receive the boost IC and other passive components from China. so stick around for the first prototype!

  • Rev3.1 board is out!

    TinLethax09/26/2021 at 08:43 0 comments

    on rev3 I decided to swap the LTC3459 out due to cost reason and replace it with FAN5331SX. A far cheaper boost IC. The latest schematic (rev2) and board (rev3.1) are now available on GitHub and OSHPark!

  • Rev 2.2 PCB is here with some little improvement.

    TinLethax09/19/2021 at 04:53 0 comments

    I changed the ground plane from solid copper into mesh-like ground plane to improve flexibility, new rev PCB can be found here at OSHPark as well as on my GitHub repo.

  • Moving closer to first Prototype !

    TinLethax09/16/2021 at 16:03 0 comments

    Right now I be able to complete the Time / Date setting part of the watch, so overall features are

    - Display Time in this format

    Current Time:

    - Display Date in this format, Note that XX is 01-99

    Current Date:

     - Left / Right Joystick button is for navigating through menus (now only two, Time and Date).

    - To enter the setting mode, just navigate to Time menu or Date menu, and double press the center joystick button. Use Left / Right button to move the cursor (underscore as a cursor), Up / Down button for Increase / Decrease the value.

    - Leap year capable, 29th FEB supported, month 13 proof.

    - Left handed mode (still using in-code #define, Will make the proper setting menu later).

  • Something is not right...

    TinLethax09/14/2021 at 02:17 0 comments

    Update : I came to an agreement with seller that I will bought another one with some little discount. But I ended up paid full amount by accident (I should've wait the seller for the new listing ;P). So the excess is for another cheapo 128x64 OLED display. 

    yesterday I received the adapter PCB. After some code debugging I be able to get the display up and running. However, the Display panel seems broken by some unknown reason. Only middle region looks normal but around them look really faint. I use the command 0xA5 to turn all the dots on and that confirmed that the display is broken. I contacted to seller waiting for reply today after I talked with the seller last night. More about this soon but here's is the image of it up and running.

  • Watch's PCB redesign, Connector is rotated 180 degree...

    TinLethax09/09/2021 at 09:48 0 comments

    You can get the latest PCB revision by the link at README.MD here

    After long day of headache and eyestrain. I Received the connector today. Moment that I unpack it. I realized that my PCB design was wrong the whole time. instead of the connector side facing out of the board, It's facing in. So Total redesign from rev1.0 to 2.0 (still same dimension). 

  • First Watch code is here! (very WIP)

    TinLethax09/07/2021 at 14:49 0 comments

    I already code the code that will be running on the actual watch, the link included in this project link. Also here too. The code still W.I.P. and never tested since I don't receive the dev board adapter yet (forgot to order with OSHPark's super swift🤦♂️).

View all 11 project logs

Enjoy this project?



dearuserhron wrote 09/14/2021 at 21:30 point

Fflexible oled is a comodity, isn't it? I'm just try to select proper display for my project (passwords generator), and I can not use oled in production because of price, so I'll put there lcd from old nokia.

  Are you sure? yes | no

TinLethax wrote 09/15/2021 at 02:14 point

About the Flexible OLED, It's really pricey. I'm talking about the cost of x50 times of the cheap SSD1306-based OLED display. Not so sure about your production quantity. But you can get the SSD1306 as cheap as 30 cents each. You might try looking on Alibaba, these OLED are just everywhere.

  Are you sure? yes | no

Dejan Ristic wrote 09/10/2021 at 06:55 point

Will the wrist band be made out of a flex pcb as well?

  Are you sure? yes | no

TinLethax wrote 09/11/2021 at 02:58 point

Probably not (yet). I planned to use some kind of Velcro-like wrist band and just stick the PCB and display onto it.

  Are you sure? yes | no

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