"Let's make GD ROM emulation happen" Facebook group.

VA01 using Retrobit VGA with 300Ohm resistor
Have not noticed any issues. I should say that the screen is slightly shifted to the right so the right side is cut off, but I can't say that this is not my TV as it is a projection. I will get around to verifying this on a LCD.

 

If I could properly tell colors I would...Resistor labeling schemes are a nightmare to the partially colorblind and I'm afraid I don't have any sitting around that are already labeled. I'll see if I have some with long enough legs, maybe I'll send you some pictures and you can help me verify them.

 

It wouldn't help to use a smaller resistor, it'd only draw more current. The idea of using a resistor is to stabilize the 12v-line of the PSU that wasn't design for an open load. Ideally, you'd use the biggest resistor that stabilize the output of the PSU around 12v.

 

Oh yeah...duh, it's going straight to ground...

 

I can't tell if you're realizing the point or if you're being sarcastic.

My point is that if the 300 Ω resitor led to issues, a 60 Ω should only worsen it. I'd try a 1k or 10k Ω; hopefully it'd stabilize the voltage (leading to less heat) without drawing too much current, so the VGA-box can receive enough power.

 

No, I did realize the point, sarcasm not intended.

 

It really seems like some variations in psu. Just recommend no resistor as the vga box should use the 12v.

In testing 3 different systems for days with and without resistor the spike was 5 degrees higher then running a stock system. Mesured with 3 thermocouples all internal.
Above drive, at drive and board level. I took in accounting the ambient temperature changes to account for the correct readings.

Without the actual drive in place the temperature was high on all 3 points.

 

Can you explain it little more because if the VGA box didn't have enough current how a bigger resistor would help?

 

In testing my other dreamcast I see no difference with vga so I'll leave the resistor in. Now will make comparisons with temperature.
For those with an android phone, you can download an app called elextrodroid. One of its features is that it helps you identify resistors.

 

you can use this resistor calculator http://www.digikey.gr/en/resources/...version-calculator-resistor-color-code-4-band

 

A big resistor would use less current (V=RI), leaving more for the VGA box. The resistor and the VGA box are in parallel on the 12v line.

 

True, thank you. The app I posted also has other goodies so it has come in handy for many things.

 

yes if the resistor and the vga is in parallel you are right (10 or 100K seems ok), but where did they put the resistors direct on the psu ?

also did the gdrom work in parallel?

 

Well after some testing, the dreamcast with the USB GDROM does get warmer compared to the other one but don't think it'll be a problem. Maybe I'll add a 2nd fan somewhere.

 

When you plug things on a voltage source, you put them in parallel, otherwise plugging and unplugging a single device would be a real hassle (to ensure the circuit is closed) and the voltage on each element would depend on the resistance (impedance) of the others, which would be rather impractical.

A voltage source provides a fixed electrical tension, the devices it powers are all in parallel and the current each receives depends on its resistance/impedance. If the required total current is too much for the source, tension will drop until the devices plugged stop working, just like a battery that runs out of juice.

For more detail I suggest getting an electronic book aimed for college. This isn't quantum physics or rocket science, it's pretty understandable with a high schools education and motivation.

 

so if gdrom alone consumes 200mA have 60omh resistance (R=V/I) Correct?

Q.1
why do we need more resistance?

Q.2
as you said PSU wasn't design for an open load correct, but designed to work with gdrom so if we need to emulate the resistance of the gdrom to to achieve stock load what resistor do we need?

 

You're right for the 200 mA.

The idea is not to make it as if there was really a gd-rom plugged into the source, the idea is to stabilize the voltage of the source so that it doesn't increase too much, to reduce heat. If it works with the gd-drive it should work with the 60 ohm resistor, but my point is that you should use the biggest resistor possible that stabilizes the voltage so when no useful device is powered by the 12v, as few current as possible is drawn. This has the advantage of reducing the heat produced by the resistor (P=V²/R and V is fixed) and leaving more power available for the external devices that use the 12v.

The case here was that it didn't worked with 300 ohm, it seemed like the VGA box didn't receive enough current. Decreasing the resistor would lead to the VGA box receiving even less if 300 was already limiting it.

FG

 

Well it would seem the UGC just doesn't like some HDD's.

The hdd on the left works every single time, but the hdd on the right refuses to work at all. (UGC won't initialize it at all)
http://i.imgur.com/BTii8fW.jpg

There the same make, only difference is one is 500GB & the other is 320GB.

I spent just over an hour copying over all the games only to find this out

 

Use different adapter or external power, i believe that your problem is the power, if your adapter take external power then plug an external power else use another adapter with external power

Edit: i see that both drives are reted to 0.85A so maybe not a power problem but i suggest you to test an external power supply

 

As Madsheep said, I would think power as well. Though both drives are .85A it still could be that one is below that level and therefore getting just enough power to work. Another that that may be good to verify is that these drives are defragmented. A normal file copy to the drive will write the files wherever the drive's head is which makes for a faster write, but when you load the game the files will be scattered all over the drive. I imagine that this could also be an issue if your DC isn't getting the proper files quick enough. Of course each drive has different seek times which could also effect this.