Discussion in 'General Discussion' started by thedrew, Oct 9, 2017.
Output, not input.
Oh well. I must have read it wrong.
Sweet deal! I bought a second one for $10 and he shipped 2 (again). So I’m at 4 screens for $20!
I have the feeling this guy is trying to offload his stock a la Fruity_Grebbles. Either that or he thinks he’s gonna hustle the scene by hooking us on cheap screens before jacking up his price. Oh well, get em while they’re hot!
Hey @fibbef , could you measure how many watts the screen and board use for me?
Sure, I’ll try to get that for you this weekend.
@The Save State Gamer i still haven’t forgotten about you. Just haven’t had a chance to set up retropie yet plus my 4GB+ microSDs are currently in modded DSes. I’ll look into picking up a cheap card tonight.
Finally got around to doing the additional testing that I promised.
A few voltages that I measured. If you see any other spots that look like they need tested, let me know.
The RetroPie config screen to show how text appears. Honestly, it looks like crap. But then again, it looked like crap on my 27" CRT.
Mario 64 still looks pretty good, albeit the emulator seems to want to use much less of the screen area than is available. This is on stock settings. I'm sure you could tweak it to use those additional pixels.
Mario World isn't bad, but again issues with using the right amount of screen. This time it looks like the video is crunched vertically, making it look stretched on the horizontal axis. I went into the emulator settings and selected 4:3 NTSC but I guess that's what it thinks it's already doing because it looked the same. Might try 4:3 PAL just to see what happens.
When I was copying ROMs over, I had forgotten that I did some Genesis games originally, so I tried some NES instead. Contra looks more or less as it should. Maybe the slightest vertical compression like with the SNES emulator, but for some reason I didn't notice it as much.
@MasterNate I felt pretty confident that I could measure watts used by reading the current draw, but in the end, I have no idea what I'm doing. I'm only good for finding resistance, continuity, and voltage. Here's a pic of my meter, so if you want to walk me through finding the power draw of the screen, I'd be happy to give it another go.
Spin it to point to either 200m or 10 on the A setting on the bottom left (that's DC amps). Then pull your red probe out and jam it into the "10A MAX" port. Connect the meter between the power supply and the screen (eg the black probe goes to the + power in on the screen, and the red probe goes on the + power out on the power supply). Then, just multiply amps * volts to get watts.
Yeah... That's the kind of crap I've seen with RetroPie and other composite screens (like the ones I've used). But, it still seems that these screens are popular for everyone's obligatory, limiting GameBoy shell with OG buttons Raspberry Pi portable. [Seriously, there is not a lot of creativity going around when it comes to Raspberry Pi portables, which is why we need more good ones on BitBuilt ] Ultimately, the best alternative is a small HDMI screen. A few years ago, these didn't exist, but you can now find 3.5" 4" 4.3" and 5" HDMI screens for Raspberry Pi on places like Amazon and Ebay. Of course, most people aren't willing to rewire an HDMI port, but I don't mind! (Surprisingly, HDMI, the better quality signal over composite, takes less processing power on the Pi's part to produce, so HDMI is the best choice anyway.)
Ultimately though, there is a way to resize the emulators in RetroArch, and this is documented on the RetroPie Github pages somewhere. But, I probably wouldn't really go any further with the Pi because I don't think the results will be any good in the end.
But, I am still interested in the screen, and so for additional points to test, there seems to be a VD3 pin at the top of the board (along with a ground), and if you could read the voltage across these pins we could find some promising data. I would think by the label, that this is connected directly to the 3.3v line that the chips actually use.
Here's my little contribution. I think this screen is great and to be honest is the best 3.5" screen running composite I've seen. It's really sharp for composite and the colors are rich as well. It was hard to take pictures of the screen but here they are. My camera had a hard time focusing also.
The text is very legible as well. There are also solder pads for pots to adjust the color, brightness, and contrast that I just started messing with and made it look even better which I didn't take pictures of. I have a 3.5" 640x480 LCD as well and I actually like this one better. The only slight issue is that it can run off 5v or lower, but the backlight is so dim unless you have it running on 7.5v or higher. Currently my setup is a 3.7v battery with a voltage booster to 9v and works perfectly.
How would I go about figuring out if this display can run properly off less that 7.5v? I’ve got some of the boards I want to start using, but it would be way easier if I could get it to run from 5v or 3.3v.
Easiest way is to look at the driver board and find the chip with 8 large legs. That's normally the regulator that steps the input voltage down to 5v. You can use a multimeter to check the voltage of each pin. Once you find one outputting around 5v, you can just wire your 5v supply to that pin, forgo higher voltage and it'll run. Just be REALLY careful when checking the pins. I've killed boards by accidentally bridging 12v to 5v with a slip of the multimeter tip.
Slick, thank you!
For anyone else wondering the same, I did some testing and found you could use either of these two points (in red) as a 5v input to make the display function. They are both continuous on the same line so it shouldn’t matter which one, but the larger of the two might be easier to solder too.
Check the voltage coming out of that 3 legged component you have marked, that could be the 3.3v reg.
For anyone still thinking of getting one of these, it looks like the seller stopped selling them individually. However, you can get a lot of 10 for $50. At $5/screen, how can you go wrong? I’m thinking of doing that and being set for life.
for those who want that but are too lazy to find.
They also have a 100 screens for 600$ which is kinda weird because it's more expensive
When I got mine I made an offer as well that got accepted, so you may be able to make an offer of less than $50 and get a better deal!
So did anybody ever figure out if this screen can be run off 3.3v? And did anybody find out how many watts this runs at? Because if it could run off 3.3v, that would be very convenient, and more efficient because it doesnt have to go through another voltage regulator.
I tried what stitches suggested, but it didn’t seem to work. I’ve only been able to get 5V out of it. If anyone has any other ideas I’m happy to try though!
5v is great too. I just have a hunch that the voltage regulators on that board are not very efficient. So if we could bypass another component, the watt usage of the screen and board will go down.
If you have the screen with you, could you measure the current going to the 5v input? That way, we could estimate the power usage.
That through-hole pin labled VD3 is most likely a direct connection to the internal 3.3v line.
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