RGBHV to RGBs to use the Time Sleuth on a CRT

In my previous blog I showed you how to make a dongle which converts RGBHV to RGBs. We saw that this was very useful for use with a GBS-Control. Due to the system’s off the shelf hardware, it only outputs RGBHV and if you want to use the signal on a regular 15khz CRT, you are going to need RGBs.

There are other uses for this dongle too. Another great use case is paired with a Time Sleuth for testing 480i and 240p on CRTs.

The Time Sleuth was created by Dan “citrus3000psi” and is a monitor lag tester. It generates it’s own test pattern over HDMI. You then plug that into your TV and hold the device up to the screen. The Time Sleuth has a small light sensor in the bottom and detects when the screen shows that test pattern. By doing this, the device measures the round trip time of the signal aka. “the lag” (well you might say it measures “display lag” to be more precise).

If you find the right spot the lag can show as low as 000.01 however I was having trouble balancing the Time Sleuth and my camera

The Time Sleuth outputs HDMI however, what if you want to test it on older screens which accept 15khz? It can output 480i and 240p over HDMI, but we need a way to convert that to RGBs SCART or just plain RGBs via a BNC breakout.

We can set the Time Sleuth to output 240p and then use a cheap HDMI to VGA dongle. This works very well but gives us RGBHV, which is not quite RGBs. As I discussed in my first article, the difference is the sync signals. RGBHV uses 2 wires for sync, whereas RGBs uses one wire for sync.

Cue the entry of the RGBHV to RGBs dongle I created in my previous article. This is a simple device with male d-sub on one end and female d-sub on the other. All the signals are passed through, beside H sync and V sync, which are combined together with a simple circuit into C sync.

If we go Time Sleuth -> HDMI to VGA dongle -> RGBs dongle, then we have a reasonably compact setup which allows the Time Slueth to work on regular 15khz CRTs.

WHY would we want to lag test a CRT??

  1. Create a baseline measurement: You know it’s going to show a very small number (1ms or less). It’s true there may be little use in lag testing a CRT on it’s own. However, this chain can become a baseline, you have proved this is lag-less. Maybe you have another device you want to test the lag for? Add it into this chain and you know any new lag is coming from the device.
  2. What about component video?? You can convert HDMI to component using 1 box and then send that into a TV. This is true! If you have a HDMI to component converter and a TV which accepts component, then this solution is very easy and gives you an equivalent result. The choice is yours, does your system allow you to input component or RGBs? I am in Europe so I am on team RGB.

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