975 7x8 Charlieplex Array Controller
975 : 7x8 Charlieplex Array Controller
- Author: Wadood Wasay
- Description: Custom controller for Adafruit Charlieplex LED array board
- GitHub repository
- Open in 3D viewer
- Clock: 50000000 Hz
How it works
This is a controller for an Adafruit Charlieplex LED array. The Adafruit arrays are larger than can be controlled with 8 bidirectional bits, so the maximum size of LED that is controllable with a Tiny Tapeout project is 8x7, or 56 LEDs. When enabled and connected to the first 8 pins on one side of the Charlieplex array, the default display is a brightness gradient from one side to the other. The SPI interface can be used to input a different display.
Because LEDs in the Charlieplex array can only be addressed one at a time, the brightness is maximized in this implementation by turning each LED on for a duration proportional to the brightness. That makes the brightness value relative to the number of LEDs that are on.
How to test
Connect the 8 signal pins of the bidirectional I/O PMOD to the first 8 pins on one side of the Charlieplex array. On reset, the display will turn on all LEDs with a brightness gradient from one side to the other.
The LED display can be customized by an input of data through SPI. The project has a 3-pin SPI interface, with clock on ui_in[0], cs_n (chip select, sense negative) on ui_in[1], and MOSI (SDI) on ui_in[2]. There is no MISO pin (project SPI slave does not generate any output). Input starts after the falling edge of cs_n. Input is up to 56 byte values, one per pixel. The lower 4 bits are the LED brightness (0 to 15), and the upper 4 bits are ignored.
External hardware
Adafruit Charlieplex array (plain, without a controller) https://www.adafruit.com/product/3162 or equivalent (comes in a number of colors, some of which may not be in stock).
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | SCLK | LED0 | |
| 1 | CS_N | LED1 | |
| 2 | MOSI | LED2 | |
| 3 | LED3 | ||
| 4 | LED4 | ||
| 5 | LED5 | ||
| 6 | LED6 | ||
| 7 | LED7 |