405 lines from Raspberry Pi 5

[Mike Watterson]

I wonder how the Pi does PAL/NTSC encoding and composite sync generation. If it's all very programmable then that's good for odd standards. If it's like the PAL/NTSC output from many PC video cards it's fixed to 625/50 and 525/60. That's why the 405 etc solutions using PCs have to use the VGA output and do a very approximate vertical sync waveform.

I don't know. I can experiment and look at it with 'scope.

I was suspicious of my modulator as it had a Euro plug, not US. A search online suggests it's VHF 625 with 5.5 MHz audio.

The PSU is a 22K resistor, rectifier, TO92 transistor and tiny transformer like transistor radio audio driver, but no IC. No obvious feedback. The transformer feeds a rectifier and 390 uF 25V cap for modulator supply.

The case has 220V and double box symbol. No certifications and only sold on Asian & African sites plus ebay. I've never plugged it in and suspect I won't without bypassing the PSU with DC!

Looks like fixed coil for VHF (so random channel) and transistor IFT style tuned coil, probably for 5.5MHz FM. Three SM transistors on that part of PCB