Measure video level with AD

[Andrew Wilson Jones]

Is the AD on any of the PIC fast enough to measure the voltage of a video wave form. On a PAL system If I count the sync pulses to get the required line then have a delay to get to a point on the line can I then use the AD to measure the voultage at that point. IE if I wanted to measure the Green bar of a coulour bar display. Each line on a PAL system is 64us long - front porch, back porch, colour burst etc leaves about 52us of signal / 7 colour = 7.5us over which the green is present. If not is ther any other way I could measure its level.

Thank Andy
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This message was ported from CCS's old forum
Original Post ID: 144516172

[John Taylor]

This is simply a sample and hold problem. In the PIC A/D you charge a S/H cap in the PIC via a MUX from which the conversion is then done on. As long as the signal is present long enough to charge the S/H cap and you don't expect to do another conversion quickly there isn't a problem. What it really comes down to is the impedance between your signal and that cap, such that it has time to charge to the same value as your signal. A way to ensure this is to buffer the signal with an amplifier to present a low impedance to the A/D or to do an external S/H to eliminate the timing. The only real constraint is to not need to do conversions faster than the SAR clock allows.
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This message was ported from CCS's old forum
Original Post ID: 144516181