honestbob wrote:I just tried to reproduce natshaw's initial test with connecting pin 3 of daughterboard connector to a 470ohm resistor to ground then across to the green (Y) input on my 29" Panasonic CRT TV. No picture. I don't have another convenient test TV unless I shift everything up into the family room so I guess I'll have to wait for the op-amps to arrive to test further.
natshaw wrote:honestbob wrote:I just tried to reproduce natshaw's initial test with connecting pin 3 of daughterboard connector to a 470ohm resistor to ground then across to the green (Y) input on my 29" Panasonic CRT TV. No picture. I don't have another convenient test TV unless I shift everything up into the family room so I guess I'll have to wait for the op-amps to arrive to test further.
Ah, you might have reproduced blowing up the VDP there. Resistor must go from pin 3 to your RCA lead directly. Don't connect it to ground, otherwise you're got 2 loads in parallel, one of which is only 75 ohms, then VDP will probably die.
honestbob wrote::) Yes, I figured that out after the initial test when I double-checked the resistor value and got a shock that it was reading about 65 ohms. It took me a while to figure out that the TV gave me a 75 ohm resistance in parallel across that resistor. I guess the 470ohms to ground recommendation from the datasheet relies on having something like an op-amp with massive input impedance between you and the output, or if you are using AC coupling or similar.
I bought a CA3130 (higher b/w sibling of CA3140) from Jaycar yesterday, hooked it up (also as 2x gain), but am getting flat-line 1.4V output. Hmmm, not sure what's going on there, maybe my voltage divider (for gain) resistors are both too high. Will lower both down and see what I get.
honestbob wrote:There is a TV with a SCART connector at my parents place, so I'll borrow that.
natshaw wrote:Hope it's SCART with RGB! Have had SCART before that doesn't implement full spec, or does odd stuff like using component in via the RGB pins etc. If you wire up those voltage signals onto SCART also, you'll get auto-input selection if the TV supports it.
natshaw wrote:Pin 3 of daughterboard, to a 470 ohm resistor, to green (luminance + sync) socket on component video (DVD) input.
This gives about correct impedance for the VDP chip to drive. However, signal is not 1 V p-p, it's more like 0.25 V. Quality device like Sony TV can just understand signal. Dell monitor with component inputs cannot.
honestbob wrote:R-Y Trimpot - So that scales the input to the amp by 190/535 = 0.355 (that is then multiplied by 2 by the amp = 0.71 * original signal)
B-Y Trimpot - So that scales the input to the amp by 97/473 = 0.205 (that is then multiplied by 2 by the amp = 0.41 * original signal)
Y Trimpot - So that scales the input to the amp by 203/545 = 0.372 (that is then multiplied by 2 by the amp = 0.744 * original signal)
(edited initial copy-paste error in above - oops)
honestbob wrote:So that scales the input to the amp by 203/545 = 0.732 (that is then multiplied by 2 by the amp = 0.744 * original signal)
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