tofro wrote:It's just that on the QL, it's absolutely easy, as it only has max 8 colours (That is, R,G, and B are either on or off).
On computers like the Spectrum that have an additional brightness signal that you need to mix into the R.G, and B signal, it is a tad more complicated.
Thank you Tobias, that really clears it up. So on the QL it just sends a high or low signal on each of the 3 lines giving you the 8 possible colors (black and white being on the extreme end of all-on or all-off). So sending this signal to an analog line you step down the voltage to have its intensity be something reasonable that appears on screen.
Exactly. The 5Volts from the QL RGB are simply "eaten up" using a voltage divider consisting of the added resistor and the impedance of the monitor input, ending up at 0.7V or 0V on that input.
On the Spectrum 128, you need to add a bit of circuitry that pulls the R, G, and B even further down (by another 0.35V) when the BRIGHT signal is low, to give half brightness, thus 16 colors.