968 Charlieplex array controller
968 : Charlieplex array controller
- Author: Tim Edwards
- Description: Charlieplex LED array controller with UART programming
- GitHub repository
- Open in 3D viewer
- Clock: 10000000 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 UART 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 overall brightness somewhat 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 (see the pinout diagram, below). 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 UART. The project has a 1-pin UART interface (receive only), with Rx on ui_in[0]. The baud rate is set to 9600 for the default 50MHz clock. Inputs are ASCII characters. Values '0' to '7' set the LED brightness (3-bit encoding), and values 'G' and higher set the pixel address to modify. Every value auto-increments the pixel address by 1, so the display can be cleared by sending character 'G' followed by fifty-six characters '0'. The UART format is 8 bits data with 1 start and 1 stop bit (standard).
The FPGA implementation of the project (see directory fpga/), designed for an Arty A7 development board, has an accompanying script "usb_driver.py" which connects to the project through USB from a host computer.
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 | ser_rx | LED0 | |
| 1 | LED1 | ||
| 2 | LED2 | ||
| 3 | LED3 | ||
| 4 | LED4 | ||
| 5 | LED5 | ||
| 6 | LED6 | ||
| 7 | LED7 |