293 Algorithmic Pattern Generator
293 : Algorithmic Pattern Generator
- Author: Olonade Kelvin
- Description: Autonomous VGA + Audio visual synthesizer with 8 algorithmic scenes, LFSR-driven pattern evolution, and bytebeat audio.
- GitHub repository
- Open in 3D viewer
- Open in VGA Playground
- Clock: 25000000 Hz
How it works
DemosceneTTSKY is a fully autonomous VGA visual synthesizer. It generates a 640×480 @ 60 Hz video signal entirely from logic gates, with no RAM, ROM, or CPU.
- VGA Timing Generator – Two counters (
x0–799,y0–524) create precisehsyncandvsyncpulses for a standard VGA monitor. - Render Engine – Every pixel’s colour is computed on the fly using one of 8 hardwired bitwise equations that mix the
(x,y)coordinates, a frame countert_frame, and a shift amount. The equations use only shifts, XORs, ANDs, ORs, add/sub, and a single multiplication. - Autonomous Show Controller – A 16‑bit Linear Feedback Shift Register (LFSR) generates pseudo‑random numbers. Every 60 frames (1 second) a new random value is captured and used to change:
- the active visual equation (3 bits),
- a global shift amount (3 bits),
- the colour palette mapping (2 bits). This makes the chip a self‑directing “video jockey” that never repeats.
- Palette Mapper – The 8‑bit pixel value is mapped to 6‑bit RGB (RRGGBB) using one of four selectable palettes (natural, channel‑swapped, muted, inverted).
- Audio Bytebeat – A separate 16‑bit counter runs continuously. During the blanking intervals of the video signal, an 8‑bit audio sample is output on the bidirectional pins, driven by a Bytebeat formula
(high_byte >> shift) ^ (low_byte & mask). The audio parameters also change every second using the same LFSR.
How to test
- Provide a 25 MHz clock on the
clkpin. - Pull
rst_nlow for at least a few clock cycles, then release it high. - The chip will immediately start producing a VGA signal on
uo_out:uo_out[7]: vsyncuo_out[6]: hsyncuo_out[5:0]: RGB (2 bits per channel)
- Connect these pins through a simple resistor‑DAC to a VGA monitor. You should see a 640×480 image with slowly evolving fractal patterns.
- The LFSR automatically changes the visuals every second – no external switches required.
- To observe the audio, connect the bidirectional pins
uio_out[7:0]to a speaker via a DAC. During the video blanking periods, these pins output the Bytebeat audio. (Theuio_oesignal is high during blanking, low during active video, so the pins are safe to share with other circuits.) - The
ui_incontrol switches are not used by the autonomous mode, but you can connect them to override the LFSR for manual control if you later modify the design.
External hardware
- VGA monitor (or a VGA‑to‑HDMI converter)
- 6‑bit resistor DAC for RGB (e.g., 2 resistors per channel: 330 Ω and 680 Ω on each of the 6 colour lines, plus 75 Ω termination in the monitor)
- Optional: audio amplifier + speaker (connected to a separate R2R DAC on the bidirectional pins, enabled only during blanking)
- 25 MHz crystal oscillator (provided on the Tiny Tapeout demo board)
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | Shift amount bit 0 | R1 (Red MSB) | Audio bit 0 |
| 1 | Shift amount bit 1 | G1 (Green MSB) | Audio bit 1 |
| 2 | Shift amount bit 2 | B1 (Blue MSB) | Audio bit 2 |
| 3 | Shift override enable | VSYNC | Audio bit 3 |
| 4 | Mode override enable | R0 (Red LSB) | Audio bit 4 |
| 5 | Mode bit 0 | G0 (Green LSB) | Audio bit 5 |
| 6 | Mode bit 1 | B0 (Blue LSB) | Audio bit 6 |
| 7 | Mode bit 2 | HSYNC | Audio bit 7 |