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reDOT_smart

smart miniature (DIP6) 5x7 LED Matrix

al1
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This is what happens if you put the #reDOT and a small microcontroller on one PCB. This is in DIP-6 form factor. Controlled by UART. Power supply pins are available on both sides for easy building of multi digit displays.

This project is based on my #reDOT

project. Basicly it is a 5x7 SMD LED Matrix an a microcontroller on one PCB. I started wirh 0201 LEDs (see first project log), but this was not reliable. So a second version with 0402 is in development. 0402 LEDs do have some benefits over 0201:

  • bigger and you can solder them better
  • cheaper
  • more colors availible

The microcontroller (a low coast STM8) drives all LEDs directly with multiplexing. For controlling a UART interface is available. The dimensions are like a DIP-6 package. For easy connection of multiple PCBs, the pads are castellated. Also the supply rails are available on both sides. So multiple of these display can be soldered together to a bigger display without the need of additional wiring.

This is planed as chainable. Therefore connected pins for the supply rails are available on both sides. The idea is to solder them together like I did with #tiny7. The RX pin of the second display would be connected to the TX pin of the first one (the most left one). So the firmware must implement some kind of UART-shiftregister to control all displays with same firmware

     MASTER                  DISPLAY #1          DISPLAY #2
+-----------------+          +--------+          +--------+
|    UART-USB     |---+5V--->|VCC--VCC|---+5V--->|VCC--VCC|  
|    or other   TX|----->----|RX    TX|--------->|RX    TX|->
| microcontroller |---GND--->|GND--GND|---GND--->|GND  GND|   
+-----------------+          +--------+          +--------+  
             unneeded data flowing out at the end of the chain

Project is not yet ready. For prototyping specially for the software #reDOT and a cheap chinese development board with a STM8 will be used (see also there for a early version of the firmware)

  • 35 × SMD LEDs (0402 or 0201 depens on version) Tiny LEDs
  • 1 × STM8S003 Tiny and cheap MCU in UQFN package
  • 1 × misc 0402 resistors and capacitors

  • New 0402 LED version

    al103/27/2017 at 20:10 7 comments

    Soldering the 0201 on double sided populated boards was a fail (see last log). But here is the solution: 0402 LEDs. The board will be with 300x390 mil a little bit bigger than the old one (300x340). But hope that the 0402 LEDs are easier to solder. And they are much cheaper also.

  • 0201 version fail

    al103/27/2017 at 16:24 0 comments

    The first version of this was planed with 0201 SMD LEDs as I used them on the 0201 version of #reDOT

    but there are a few problems:

    • my hand-manufacturing yield to bad: with 50 LEDs I had to few to populate all 35 successful
    • reworking is quite difficult
    • when populating the one side the other side could get messed up, specially the LEDs get de soldered quite fast.

    So I decided that 0201 LEDs on PCBs with parts on both sides are out of my specifications. And i will use 0201 only on single sided populated boards in the future.

    Here are some of images of the partial working prototype, as you can see some LEDs are missing and some other would need some rework:

    But this project will go on: I am working on a 0402-LED version. with nearly the same Form Factor.


    Old image/text dump:


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davedarko wrote 01/05/2017 at 20:20 point

no. No you didn't.

[edit] is it chainable?

  Are you sure? yes | no

al1 wrote 01/05/2017 at 21:56 point

yes. At least is that the plan. Therefore connected pins for the supply rails are available on both sides. The idea is to solder them together like #tiny7. The RX pin of the second display would be connected to the TX pin of the first one. So the firmware must implement some kind of UART-shiftregister to control all displays with same firmware

  Are you sure? yes | no

Ted Yapo wrote 01/05/2017 at 22:05 point

This is a very cool project.

I made a similar UART network display some time ago - much larger, of course, and with 7-segment LEDs.

I ended up sending a small 3-byte packet of data.  The first byte is a destination address (which display), the second byte is a command code, and the third byte is data.  Each display receives a packet either from the host or its neighbor, and if the destination address is zero, executes the command code.  If the address is >0, the display decrements the address and sends the packet to the next display in line.  It works pretty well, and you could chain 256 of them together.

  Are you sure? yes | no

al1 wrote 01/05/2017 at 22:17 point

Thanks for your comment. That is a nice idea for protocol.

In my first prototype I am just sending ASCII chars. The font is stored locally on the display. The old char gets send to the next display. So you get some kind of shift register. But I am also limited to 256 different characters.

So sooner or later I will use some protocol. Specially for controlling brightness and addressing each Led individual .

  Are you sure? yes | no

Ted Yapo wrote 01/05/2017 at 23:09 point

Your comment about brightness reminded me - I reserved address 255 as a "broadcast" - every display executes the command and passes the broadcast message on.  I did this for implementing brightness controls, so they all change with just one packet.

  Are you sure? yes | no

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