A alternative approach to create a multi digit 5x7 LED Matrix Display

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Maybe you know my #redDOT_smart project. There I used one STM8 to control one 5x7 LED-Matrix. But what if you want 5 or even 8 5x7 Matrixes to display longer Strings? Using one Microcontrolller to control all Matrixes instead of one each looks better for me

Idea besed on my #reDOT_smart and #reDOT . But with a approach to crate bigger "strings" of Matrixes to Display Strings. I am thinking about two components:

  1. 5x7 Matrix Board: One PCB with one Matrix on it. With castellated holes at the edge to solder it on the main board.
  2. Main board: Board with Controller, maybe some shift registers, drivers, interface and so on. 5 or 9 Matrix boards will get soldered on this board. 

Main Milestones:

  • Design and order 5x7 Matrix Board.
  • Assamble the Matrixboard and test it
  • Design Main board
    • choose a  Microcontroller
    • Define Interface: Uart?
    • chose LED-Matrix driving scheme
    • Decide how man Matrixes per Mainboard
  • Order Main board
  • Assemble everything and show some ideas for use cases (I do have already one specific in mind, more later)  

  • State of the Matrix

    Alex05/12/2018 at 23:21 0 comments

    Here are some quick images of the current Hardware state: The Grind in the background is 5mm (~0.2'')

    Two matrix-PCBs are soldered. They are also working, but I have no good images so far. 

    The back with the two LED driver ICs, a STM8s microcontroller, pinheader for ESP-01 and USB-connector for power

     Can you spot the mistake on the next image?

    Saw it?  The LEDs on the third not soldered Matrix PCB are soldered 180° rotated. This does not work with the main PCB. But sadly the cathode marking on the matrix PCBs is wrong. And I soldered the first five matrix PCBs wrong for the main PCB. With five not usable matrix PCBs I run out of LEDs sadly :(

    Like this it should look at the end. 

    Now I will work on the STM8 firmware. So far only switching all LEDs on is working. 

  • First matrix PCBs soldered

    Alex04/12/2018 at 21:46 0 comments

    If you follow me on twitter (@tinyledmatrix) you could already know these pictures. I soldered the first five matrix PCBs. At least a quick diode test with the multimeter was positive. PCBs for the main PCB should arrive tomorrow, if the tracking is correct. So more soldering work to do on the weekend!

  • Update

    Alex04/05/2018 at 20:04 0 comments

    Some short updates:

    1. The Matrix PCBs arrived. I will post some Images here, when I soldered one.

    2.The Layout for the Main PCB is ready! I ended with a pin header to use ESP-01 Modules for the connectivity. Here some nice renderings:

    The front LED side with five LED PCBs. Here in red

    The Pack with all the LED control Stuff, an STM8 Microcontroller and a pin header to add wifi with an ESP-01:

    Like This it should look with an ESP-01:

  • Placement Tests

    Alex03/21/2018 at 22:10 0 comments

    Some First Tests:

    • The main board is sadly to small to fit an ESP-Module, so for Wifi I must got to ESP8285
    • There is enough place for all needed ICs, passives should also fit

    I will continue with routing (probably during may 6 hour train trip on Saturday) 

  • Number of Digits, Drivers, Microcontroller and Interface

    Alex03/20/2018 at 21:29 0 comments

    I did some brainstorming about Number of Digits, Drivers, Microcontroller and Interface. I ended up with the following for the the first main board design:

    • 5 Digits wich are connected as 25x7 Matrix (25 cathode columns and 7 anode rows) 
    • Driven by:
      • two 16-Bit constant current low side drivers (MBI5026  or similar)
      • one 8-Bit source Driver (probably MIC5891) in the same SPI bus
      • OR one logic demux with p-fets or driver directly controlled by GPIOs
    • One low cost 8-Bit MCU (probably some SMT8S) 
      • doing all the LED multiplexing
      • UART and/or I"C as control Interface
    • ESP8266 Module 
      • because everything needs wifi
      • Maybe ESP8285 to safe some space

    I hop all these ICs will fit on the back of 5 Digits. I will try this the next days.

  • Matrix PCB layouted

    Alex03/15/2018 at 18:05 0 comments

    For this project I will use Matrix-PCBs. These Matrix PCBs will get soldered on the main PCB. Main features are:

    • 5x7 0402 LED Matrix
    • no components on the back
    • castellated holes (50mil /1.27mm pitch) on the sides to connect to main PCB

    I also orderd some PCBs at OSH-Park to test this. The LED Matrix itself is the same as the latest Version of #reDOT_smart  but this project will see no update. 

    The rendering (made with eagleUp and SketchUp) show two of the Matrix PCBs side be side, as they will get mounted on the Main PCB (castellated holes not shown right) .

    Further on I will design the Main PCB but I did not decided many things there. For example one main/important decision would be the microcontroller. My favorites so far would be

    •  ESP8285 - to get wifi 
    • Atmega328P - the classic one
    • SAMD09/11/21 - modern Arm core, but maybe little bit overkill
    • PIC16/18 with USB - it looks like implementing USB on PIC is easier then on SAMD11/21

    Do you have any thoughts about this selection or do you have an Idea for an additional microcontroller to consider? Than please leave a comment!

    Based on microcontroller Selection I will chose additional components like Shift registers to expand IOs, led driver, clock stuff, power connector, interface connector an so on. 

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Nixie wrote 04/19/2018 at 06:47 point

Woah! They look super neat!
Might buy some just for fun! (I have a project in need of a retro display like this, but it has to be bigger (20x80mm), but they look really cool nonetheless.

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