LED heart

Geek's Valentine card with LED 8x8 pixel display

Project structure

├── README.md
├── img
│   └── *.png
├── bitmap_img                      # files, that will be converted to bitmaps
│   ├── fonts                       # fonts directory
│   │   └── basic                   # "basic" font directory
│   │       ├── font_map.json       # images and letters map
│   │       └── *.png               # letters images
│   └── *.png, *.txt, *.h
├── bitmaps_generate.py             # bitmaps generation script
└── firmware                        # microcontroller firmware (PlatformIO project)
    ├── Makefile
    ├── include
    │   └── bitmaps.h               # automatically generated bitmaps
    ├── lib
    │   └── DisplayMax7219
    │       └── DisplayMax7219.h
    ├── platformio.ini
    └── src
        └── main.cpp

Hardware

Name	Qty	Link	Description
Heart-shaped PCB	1	Gerber files	EasyEDA project
Attiny13A	1	Aliexpress
MAX7219	1	Aliexpress	LED matrix driver
0805 white LED	64	Aliexpress
CR2032	2	Aliexpress
CR2032 holder	1	Aliexpress	2 batteries in one holder (3V isn't enough)
SMD button	1	Aliexpress	For mode switching
10k R0805	1	Aliexpress
~500k R0805	1	Aliexpress
10uF C0805	1	Aliexpress
2 positions switch	1	Aliexpress	Power switch

You will need USBasp or something similar to upload the firmware.

Soldering

Soldering 64 LEDs with soldering iron might be quite challenging, so I advise you to get hot air gun and soldering paste.

SMD nominal values:

PCB footprint	Nominal value
R1	10k
R2	~500k
C1	10uF

Order

In my opinion, this soldering order is most convenient:

1. LEDs and button on the face of PCB
2. Attiny13
3. MAX7219
4. SMD components on the back side
5. Power switch and batteries holder

Polarity

Note

LED's triangle on its backside must be turned in agreement with footprint on PCB (45° right and up)

Attiny13 and MAX7219 also have polarity. You need to match keys with keys on the footprint.

Software

Requirements

• PlatformIO
• Python 3
• GNU make

Build

To build the firmware run this inside firmware directory:

make

Uploading firmware

I recommend not to solder ICSP pins (6 pins group at the top of the PCB). It is enough to hold pins manually to upload firmware.

Note

If your Attiny is new, write fuses firstly (this will set necessary internal oscillator frequency):

make fuses

Upload or reupload firmware:

make upload

Images and text

Bitmaps are automatically generated from files in bitmap_img directory. Each file corresponds to one bitmap. You can add your own there or edit given files. Generated bitmaps are written to header file firmware/include/bitmaps.h. Each bitmap is a byte array and has name of source file in caps. For example, bitmap generated from file example_bmap.txt will be named EXAMPLE_BMAP.

Inside bitmap_img there is a font directory. Currently there is only one font, called basic. It supports English and Russian capital letters, numbers, punctuation marks and some additional symbols. Actually, you can create your custom font. I will give instructions below.

Custom bitmaps

So, bitmaps can be generated from 3 types of files:

• .png -- image will be converted to black and white. White regions are enabled LEDs. Height must be 8 pixels, width N*8 pixels. N - is number of frames. Multiple frames in one bitmap is used for slideshows or blinking animations.
• .h -- text from these files will be simply pasted to header file.
• .txt -- text for running line mode. File must contain 2 lines:
  1. Font name, e.g. basic
  2. Text, e.g. I love you♥. Allowed symbols are listed in font map file (bitmap_img/fonts/<font_name>/font_map.json.

Custom font

You can create your font or add symbols to basic. In font directory must be a font_map.json file. It tells generator what .png file it must use for specific symbol.

E.g.

"♥": "heart.png",
"+": "plus.png",
"-": "minus.png",

Images height must be 8 pixels. Width can be any. Generator puts 1 empty column between symbols, so you don't need to add empty columns to images.

Bitmaps usage

You can use bitmaps inside of C++ code. The main part is here:

firmware/src/main.cpp
=====

    ...

        switch (mode) {
            case 0:     cycle_bitmap( 60, BITMAPS_AND_SIZE(HEART_BLINK));           break;
            case 1:     scroll_bitmap( 7, BITMAP_AND_WIDTH(FOR_SMBDY_WITH_LOVE));   break;
            case 2:     cycle_bitmap( 50, BITMAPS_AND_SIZE(HEART_MINI));            break;
            case 3:     cycle_bitmap( 30, BITMAPS_AND_SIZE(HEART_HALVES));          break;
            case 4:     cycle_bitmap( 30, BITMAPS_AND_SIZE(HEART_MESSAGES));        break;
            default:    mode = 0;                                                   break;
        }

    ...

You can add new modes and bitmaps here. There are two types of animations:

• cycle_bitmap -- used for slideshows and blink animations. It will sequentially switch bitmaps from array.
• scroll_bitmap -- scrolls bitmap column by column. Used for running line text.

First argument is number of frames (FPS is set in this file) for one animation step. Second and third arguments are bitmap array and its size. You can add macro BITMAPS_AND_SIZE for cycle_bitmap and BITMAP_AND_WIDTH for scroll_bitmap.