LED Matrix

Called “panelDrive,” a Python app. Approx 2/16/2018.

• Good information

15×20 matrix of LEDs, 35 mm centers. This requires 10 meters worth. https://www.adafruit.com/product/2237?length=1 and also other sources are likely.

Raspberry Pi Buster on 192.168.0.7 has an additional driver circuit board, with a 4-conductor wire to connect to the matrix.

• Level Shifter - SN74AHCT125N (QUADRUPLE BUS BUFFER GATES WITH 3-STATE OUTPUTS). This allows the 5V LEDs data lines to be driven by the Raspberry Pi 3.3V outputs.

Used rear projection film as the best thing to cover the matrix.

Having problems with bleed through between adjacent cells. Now that I can make this with 3D printing, I can make tongue-and-groove overlapping.

From Adafruit:

DotStar LEDs use generic 2-wire SPI, so you can push data much faster than with the NeoPixel 800 KHz protocol and there's no specific timing required. They also have much higher PWM refresh rates, so you can do Persistence-of-Vision (POV) and have less flickering, particularly at low brightness levels.

Like NeoPixels, DotStar LEDs are 5050-sized LEDs with an embedded microcontroller inside the LED. You can set the color/brightness of each LED to 24-bit color (8 bits each red green and blue). Each LED acts like a shift register, reading incoming color data on the input pins, and then shifting the previous color data out on the output pin. By sending a long string of data, you can control an infinite number of LEDs, just tack on more or cut off unwanted LEDs at the end. The PWM is built into each LED-chip so once you set the color you can stop talking to the strip and it will continue to PWM all the LEDs for you

However, unlike NeoPixels, these LEDs have 2 wires (input and output) for sending data - one clock pin and one data pin. That means you need two pins, not one, to control DotStars. Because the clock and data is seperated, you can use any processor speed or type to control these strips, and you don't have to worry about being careful with the timing. Hardware SPI support is handy but not required. This makes them excellent for use with any microcontroller or microprocessor, including Arduino, Raspberry Pi, BeagleBone, Propeller, SparkCore, and any 'raw' microcontrollers/microprocessors. It's very easy to port the library, and you can send data to the pixels at up to 32MHz clock rate!

Parts list from Adafruit: