I was searching for bar generators, I found this info which I thought worth sharing.
Nice collection of patterns, gradients etc for testing in a wide range of pixel res.
ATTINY project PAL (overclocked)
Hack- (set top box to bar generator)
Not much info here but a working concept. The digibox is an Amstrad DRX300. If I find the service manual this chip must be used in other devices, DVD players too possibly.
Anyway 3.3v HIGH to pin 25 activates the colour bar setting of the chip.