An analog television station made from a pyboard and two external components.

1. A pyboard. Tested with a version 1.0 board running at 168 MHz FIXME: Test on v1.1 board
2. An N channel signal MOSFET. I used a 5LN01SP from a SparkFun Discrete Semiconductor Kit (component identification guide)
3. A small 1kΩ resistor.

• DAC 1 (X5) - outputs the video signal
• X1 - outputs the RF carrier

   (X1)──┐
        ┌┴┐
        │1│ r = 1 k ohm
        │k│
        └┬┘
         └──┐
            ├─────────── to wire antenna
     gate┃┠─┘drain
   (X5)──┨┃
         ┃┠─┐source
            └─────┐
                 ─┴─
                 ╶─╴
                  ─
                 gnd

The FET acts as a voltage-variable resistive load to modulate the amplitude at the antenna node. A short length of wirewrap or magnet wire will suffice for single-room coverage.

The magic numbers for blanking_level, black_level, and white_level were found experimentally. More greyscale range can be gotten by modifying the schematic or using a better suited mosfet mixer.

The pyboard's DAC is rated for 1 MHz operation, which corresponds to the default argument of hres=64 for the constructor. NOTE: hres should be even if progressive == False (else you'll get a jittery picture)

On my pyboard, it worked up to hres=124 interlaced but not above. After a code refactor, it works up to hres=250 progressive scan, with higher resolutions inaccessible due to both lack of available memory and DAC slew rate limitation.

progressive=False results in ~ 30 fps interlaced with 482 lines vertical resolution. progressive=True results in ~ 60 fps with 241 lines vertical resolution.

• mandelbrot set zoom

  • tilt pyboard to control cursor, press USR button to zoom in.

  • Hold USR button for > 1 second then release to double iterations.

  • Hold USR button for > 1 second, flip pyboard over, then release to toggle julia set mode.

  • It uses single precision floats so don't expect to be able to do deep zooms.