Wiring the OSSC for DIY lag testing photodiode

The OSSC has an official DIY mod to make it able to measure input lag. It involves replacing a surface mounted resistor on the bottom of the board and adding a photodiode to one of the button circuits. It's a bit hairy to work with one of those tiny surface mounted resistors. Here's some photos, with explanatory text above each photo.

After soldering you can measure at these two points to make sure that you have continuity to the button. It should show the resistance of the resistor you placed on the board. NOTE: this is the before photo, so everything looks nice and clean! You can swap the black lead to the other leg of the button to complete the continuity check, it should show about 1kohm. Best to practice this before you do the soldering so you can convince yourself you've found good test points.




Below is the after photo. Ugly as sin, but it worked. I put some tape over the circuits I wasn't going to solder so that if the board got too hot nothing would wander.



The surface mounted component is the only tricky part, really. But I was somewhat pleased how I wired up the photodiode to the board in such a way that it couldn't get (easily) ripped from the solder points.

I chose to solder to the bottom of the board, and wrap a bit of electrical tape around the speaker wire I was using to make it bulky enough.


Then I sandwiched it between the board and the bottom cover of the OSSC. The electrical tape made it snug.



In practice I'm not that satisfied with the lag tester, because it's a binary threshold device with no sensitivity control. If your TV is too bright it will respond to the backlight, and if it's too dark it won't respond to the probe. Meanwhile the lag values reported depend on which of the two extremes characterizes your display; if it's bright the trigger will happen on the very early rise in brightness, and if it's dark it will trigger only after the display has fully reached max brightness. The difference could be a couple frames, unless you are using an OLED or some other display technology with no rise time. BUT: for the effort and cost it's a pretty neat addon if you already own an OSSC. I would suggest the schematics/manufacturing be changed so that the resistor doesn't even need to be swapped out, which would leave the photodiode attachment as the only DIY aspect of this mod, which is the easier half by far.

Vizio p42hdtv10a plasma HDTV: input lag / upscaling /deinterlacing review

This 42" plasma TV dates back to 2005, with 2 component inputs + HDMI, and probably other inputs less useful for retro gamers.

Image quality

Native resolution is 720p. It's bright, sharp, and colorful, though the set I tested had some red/white snow visible on black backgrounds. It exhibits black crush, and relatively high black levels, but I suppose that could be due to the age of my set (manufactured 2006). It does show some color errors on gray gradients (some shades of gray look red, but NOT ALL). You can set 480p to be stretched to wide screen or maintain aspect ratio, but in both cases it cuts off some of the left and right edges of the input, maybe 5-10%.

Input lag (HDMI/480p), measured with a OSSC + 240fps highspeed camera

This TV has a B2W transition of  about 5ms. So the input lag varies depending on whether you wait for the TV to reach a steady state (58ms) or measure the first moment that the screen responds to input (54ms).

How I measured: I used an OSSC outputting at 480p. The OSSC lights a LED the moment it starts transmitting the pixels of a white probe over a previously black background. Using a moderately fast high speed camera (Samsung S7, 240fps) you can measure the delay between the LED lighting and the probe appearing on the screen. Since the B2W transition takes some time, the probe gets brighter over 1 or sometimes 2 additional frames.

Side note: the OSSC measures lag in a somewhat unusual way: relative to the moment the probe pixels are sent over HDMI, rather than the start of the frame. So a probe in the middle of the screen or the bottom can actually appear to have less lag than the top.  This is because the plasma takes a while to process the incoming image but then once painting begins it actually scans down the screen faster than the data is received, in effect catching up to the signal coming in over HDMI. BUT: since most dynamic sources (ie games) render the whole frame before sending it to the display, it makes more sense to measure relative to the very first pixel rendered (ie the upper corner). For those interested, the center lag is 10ms faster than the top.

Performance: Deinterlacing using OSSC

Without going into too many details... The OSSC uses bob deinterlacing for zero added lag. This looks better when you add light-dark scanlines which masks the inherent "bob" blockiness of doubling each scanline. The result looks good but darker on this TV, with very little flicker.

Built-in TV deinterlacing using OSSC

The OSSC can instead send the interlaced signal to the tv and let it deinterlace. This looks good,  better than bob though it tends to some lace artifacts. The cost is lag - an extra 35ms, for a whopping 90ms of total lag. That's huge. Enough you can feel it. But for a RPG the result is nice visuals.

Without the OSSC

The TV comes with 2 component inputs. If you plug directly into them the result is nearly as good as the OSSC.  I couldn't measure lag in this setup but I assume it's still about 90ms.

Without the remote

Don't get this TV without a remote. You cannot make any picture adjustments without it; all that remains is switching inputs and "changing volume" (but recall external speakers are required).

Panasonic PRO-505PU/PRO-1120HD plasma display: input lag / upscaling /deinterlacing review

This 50" plasma TV dates back to 2005, and is an odd beast, with a "flat" panel TV unit with no speakers and just a DVI input on back, plus a VCR sized video processing unit with all the inputs that outputs over the DVI cable. It does not work unless the video processing unit is plugged in.

Image quality

It's bright, sharp, and colorful 720p but exhibits bad black crush, and relatively high black levels. Publications of the time also called this out, so I don't think it has to do with the age of my set. In fact the set appeared to be good as new, with great uniformity and no burn in.

Input lag (HDMI/480p), measured with a OSSC + 240fps highspeed camera

This tv has a relatively slow B2W transition of 10ms. So the input lag varies depending on whether you wait for the TV to reach a steady state (30ms) or measure the first moment that the screen responds to input (20ms).

How I measured: I used an OSSC outputting at 480p. The OSSC lights a LED the moment it starts transmitting the pixels of a white probe over a previously black background. Using a moderately fast high speed camera (Samsung S7, 240fps) you can measure the delay between the LED lighting and the probe appearing on the screen. Since the B2W transition takes some time, the probe gets brighter over 2-3 frames, giving the 20..30ms value reported above.

Side note: the OSSC measures lag in a somewhat unusual way: relative to the moment the probe pixels are sent over HDMI, rather than the start of the frame. So a probe in the middle of the screen or the bottom can actually appear to have less lag than the top.  This is because the plasma takes a while to process the incoming image but then once painting begins it actually scans down the screen faster than the data is received, in effect catching up to the signal coming in over HDMI. BUT: since most dynamic sources (ie games) render the whole frame before sending it to the display, it makes more sense to measure relative to the very first pixel rendered (ie the upper corner). For those interested, the lower-corner lag is just 10ms for initial response and another 10 for steady state.

Performance: Deinterlacing using OSSC

Without going into too many details... The OSSC uses bob deinterlacing for zero added lag. This looks better when you add light-dark scanlines which masks the inherent "bob" blockiness of doubling each scanline. The result looks good but much darker on this TV, with very little flicker (probably because of the slow B2W transition).

Built-in TV deinterlacing using OSSC

The OSSC can instead send the interlaced signal to the tv and let it deinterlace. This also looks good; better than bob. The cost is lag - an extra 30ms, for a whopping 60ms of total lag. That's enough you can feel it. But for a RPG the result is excellent visuals.

Without the OSSC

The TV comes with 3 component inputs. If you plug directly into them the result is less pleasing than the OSSC. The upscaling is blockier and muddier. I've seen worse but it's disappointing for what was once such an expensive TV (msrp of $20,000!). I couldn't measure lag in this setup but I assume it's still about 60ms.

Without the remote

Don't get this TV without a remote. You cannot make any picture adjustments without it; all that remains is switching inputs and "changing volume" (but recall external speakers are required).