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Hardware:
pyb 1.0
uses:
DAC 1 (X5) - outputs the video signal
X1 - outputs the carrier
1 resistor (1kΩ)
1 N channel MOSFET (5LN01SP)
Transmitter was made by modulating X1 with X5 using a signal n-mos ('YB 4F')
from the sparkfun discrete semiconductor kit.
Diagram:
(X1)──┐
┌┴┐
│1│ r = 1 k ohm
│k│
└┬┘
└──┐
├─────────── to wire antenna
gate┃┠─┘drain
(X5)──┨┃
┃┠─┐source
└─────┐
─┴─
╶─╴
─
gnd
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.
progressive=False results in ~ 30 fps interlaced with 482 lines vertical resolution.
progressive=True results in ~ 60 fps with 241 lines vertical resolution.
Demo:
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.
Tested on a pyboard 1.0 running at 168 MHz
About
direct synthesis of NTSC signals with a pyboard
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