Skip to content

Latest commit

 

History

History
63 lines (52 loc) · 2.7 KB

hub75.md

File metadata and controls

63 lines (52 loc) · 2.7 KB
Raw

HUB75

Nyan Cat on a 64x32 LED-panel

Ledcat supports an interface loosely dubbed "HUB75", an interface used in cheap LED-pannels such as these.

Setup

To drive a single hub75 display:

  1. Get yourself a Raspberry PI, Orange PI or other mini-computer named after a fruit.
  2. Look up which physical pins have GPIO functionality in the manual of the mini-computer, these pins are typically named PA1, PA2, PAn.
  3. Connect the LED-panel to the boards GPIO pins. For each pin, note down the GPIO-portnumber (the PA-number) corresponding to the label of on the display.
  4. Tell ledcat which pin is connected to what by setting the appropriate flags:
    • The A, B, C, etc. pins should be configured using --level-select, e.g. --level-select 11,12,13,14.
    • R1, G1, B1, etc. pins should be configured using the --red, --green and --blue flags respectively.
    • Configure the CLK with --clock, LAT with --latch and OE with --output-enable

You should end up with a command that looks something like:

ledcat --geometry 64x32 hub75 \
    --level-select 11,12,13,14 \
    --red 20,10 --green 9,8 --blue 7,19 \
    --clock 18 --latch 21 --output-enable 2

Tweaking

PWM

You can optionally use --pwm NUM to control the number of PWM cycles per screen refresh. A higher value will increase the perceived color depth a the cost of refresh speed.

Multiple Displays

There are two approaches to driving multiple display segments:

In Series

Of the two methods described in this document, this is the simplest as it is synonymous to simply extending the rows further out. The main drawback of this method is that it takes longer to complete a single refresh cycle.

To use this method:

  1. Join the segments together with a flat-cable. The headers are typically labelled as JIN1 and JOUT1.
  2. Update the geometry setting, e.g. joining two 32x32 panels requires the geometry to be set to 64x32.

Note: While it is perfectly possible to physically place the displays on top of each other, ledcat currently lacks the transposition to correct the input to this configuration.

In Parallel

Displays can also be extended by connecting them in a parallel fashion:

  1. Connect the R, G and B pins to the GPIO-pins of the computer and append the pin numbers to the --red, --green and --blue flags.
  2. Connect the level-select (A, B, C, etc), LAT, CLK and OE pins to the existing wires.

Although this setup requires more effort, it should in theory result in a higher refresh-rate.