RGB to Component Video Converter
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Modifications to the RGB to Component Video Converter As both of my Foxtel and DVBT Set-top-boxes provided (only) RGB component outputs and my wide screen TV had only Colour Difference (Y, Cr and Cb) Input capability I viewed the RGB to Component Converter Project with some interest. The Kit took a couple of weeks to be become available but was assembled within a few days of its arrival and then duly connected between the above units. Alas – no picture! After looking at the “usual suspects” I began wondering about other possibilities and ultimately connected a CRO to the output of the Converter and noticed that, although the three colour difference signals were present as expected, none of them had any Sync pulses during the blanking intervals. This was the case with both STB’s! I further concluded that the TV was not providing a picture because of the lack of Sync’s. Just to verify my findings I then connected the CRO to the output of my DVD player – which did work – and, not totally unexpectedly, noticed that there were sync pulses on the Y (luminance) channel. Clearly these would need to be added to the output Y channel output of the converter. I had some previous experience using the LM 1881 sync pulse separator chip and this seemed the logical way to go. (This chip is also available as a GS 1881 from Genum). Thus, a fourth RCA input socket was added to the front (input) panel of the converter unit and a spare composite video output from the STB was applied. This could potentially be a stand-alone (RCA) output; the composite output on the SCART connector which provides the RGB signals; or the Y channel from the Y/C output – it doesn’t necessarily need to contain the chroma signal. Using a small piece of Vero board (approx 20 x 40 mm) the circuit below was constructed and attached to a vacant area of the PCB with double-sided tape. [Note that this could have been done a little more professionally – and could even be incorporated in to a Revision 2 of the Converter using available spare PCB space].
description
How to convert an RGB video signal to YRB including sync insertion. Applicable where TV does not have RGB inputs but (like most) does have YRB comonent input capability
Transcript of RGB to Component Video Converter
Modifications to the RGB to Component Video Converter
Modifications to the RGB to Component Video ConverterAs both of my Foxtel and DVBT Set-top-boxes provided (only) RGB component outputs and my wide screen TV had only Colour Difference (Y, Cr and Cb) Input capability I viewed the RGB to Component Converter Project with some interest.
The Kit took a couple of weeks to be become available but was assembled within a few days of its arrival and then duly connected between the above units. Alas no picture! After looking at the usual suspects I began wondering about other possibilities and ultimately connected a CRO to the output of the Converter and noticed that, although the three colour difference signals were present as expected, none of them had any Sync pulses during the blanking intervals. This was the case with both STBs! I further concluded that the TV was not providing a picture because of the lack of Syncs.
Just to verify my findings I then connected the CRO to the output of my DVD player which did work and, not totally unexpectedly, noticed that there were sync pulses on the Y (luminance) channel. Clearly these would need to be added to the output Y channel output of the converter.I had some previous experience using the LM 1881 sync pulse separator chip and this seemed the logical way to go. (This chip is also available as a GS 1881 from Genum).
Thus, a fourth RCA input socket was added to the front (input) panel of the converter unit and a spare composite video output from the STB was applied. This could potentially be a stand-alone (RCA) output; the composite output on the SCART connector which provides the RGB signals; or the Y channel from the Y/C output it doesnt necessarily need to contain the chroma signal.
Using a small piece of Vero board (approx 20 x 40 mm) the circuit below was constructed and attached to a vacant area of the PCB with double-sided tape. [Note that this could have been done a little more professionally and could even be incorporated in to a Revision 2 of the Converter using available spare PCB space].PICThe input (composite video) signal is terminated by a 75 ohm resistor; filtered for any excessive chroma or noise (560R and 470p); and then AC coupled to the LM1881. Among a number of outputs available the LM1881 provides a composite sync output on pin 1. This signal is then inverted through the 2N3906 and sent to the main PCB via an 8K2 resistor.This signal is then applied directly to the input of the Y signal output opamp. The value of the 8K2 resistor effectively sets the sync level at around 0.3 volts. The opamp working as an inverter then restores the sync pulses to the (required) negative going polarity.
Note that this signal is applied to the Y channel output only and, at least as far as my testing has gone, is only required on the Y signal.The nett result it all worked beautifully and I dont have to put up with the reduced resolution and crawling around the edges of high chroma pictures anymore!
