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USB dev cart project

antime - Mar 24, 2012

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		razor85	Oct 26, 2018
		Antime, since I don't understand anything about this, what voltage should I get the capacitors / resistors? How many Watts? Does it make a difference?

		antime	Oct 26, 2018
		10V or 16V capacitors with X5R or X7R dielectric will be fine. The power rating for the resistors doesn't really matter, 5V through 10kOhm will dissipate about 1/400W.

razor85

Oct 29, 2018

So...this looks ok?

https://imgur.com/a/L2hyKIZ

Ignoring the quantities (and the fact that I couldn't find 4.7 uF with 10V or 16V [max was 6.7V]). Sorry for bothering, I wanted to get the specifics right.

		antime	Oct 29, 2018
		The 4.7µF capacitor is the wrong size. You've picked metric 0603, but you need imperial 0603 (aka metric 1608). It's confusing, I know.

razor85

Oct 29, 2018

Wow, didn't noticed that! Thanks alot for the help, it's been a hell of a learning

https://imgur.com/a/1632Ni4

I think I got it right now.
EDIT: Wrong link

		antime	Oct 30, 2018
		The 10K resistor you've selected will work, but it's some special high-precision component. You can save a few bucks by using a normal thick-film resistor, like eg. RC0603FR-0710KL. Unless you know you need something special, one trick is to enter the parametrics you know, and then sort by price. The cheapest parts are usually also the ones that are used the most, and are therefore "normal".

		razor85	Oct 30, 2018
		ah I see. I wasn't sure if I needed to get a high quality one or a "normal one". Also, whats up with the tolerance values? Do I need higher tolerance components? I wouldn't think so, since this is so low voltage....am I wrong?

		antime	Oct 30, 2018
		The tolerance value indicates much much the actual, measured value of the component is allowed to differ from the nominal value. The right tolerance range to choose doesn't depend on voltage, but rather on the accuracy and precision demanded by the application. For this cartridge, the answer is "not much at all." 5% or even 10% resistors would work just as well, but you don't really save any money compared to 1% ones.

		razor85	Oct 30, 2018
		Ah I see. It's just that I didn't find most of the 1% ones. Most of the ones I got are 10%

		antime	Oct 31, 2018
		Resistors and capacitors are very different components, and the normal tolerance ranges are different, too.

		razor85	Dec 22, 2018
		Well...looks like I'm running out of luck here. I assembled my first board and was able to flash the cartridge just OK. But as soon as I plugged the USB in, my board fried (I forgot a shortened pin on FT245RL. Not nice. I assembled another board, and took the most extreme care on doing it. I connected the USB, nothing. Put it on saturn, no cartridge detected. I believe something is shortened out or simply not working, but I have no idea where to start looking. I used a multimeter and tested the resistors, and they are correctly soldered. What makes me believe is a shortened pin, is because when I put the cartridge on saturn with the console turned on, it immediatly turns off. Any tips?

SegaSaturnShrine

Dec 23, 2018

	razor85 said:

Can you snap any photos of the board including some close ups? Maybe myself or another user, will be able to visually spot a bridge or solder splash that you're not seeing.

razor85

Dec 23, 2018

	SegaSaturnShrine said:

Sure, there you go:

https://imgur.com/a/l6lnwvz

This is my first time soldering SMD, hence the horrible cap/resistor work.

		razor85	Dec 23, 2018
		By the way, I measure current and voltage on all capacitors and resistors (and measured resistance on resistors to make sure they were correct too). They only resistor that doesn't get current (when USB is plugged in) is R4. Other than that everything has current. EDIT: Is there anything I can do to make sure the IC are working? Like measuring current/resistance/voltage on some pins?

antime

Dec 23, 2018

	razor85 said:

The USB interface is not powered by the USB host, so it'll only show up on your computer when the Saturn is turned on. If you insert the cartridge, turn on the Saturn, and then connect the USB cable, is it detected on the PC? If it is, the USB part works.

The Saturn won't do anything with the cartridge until the flash is programmed. You can eg. burn an arflasher disc for that.

If you suspect a short, connect a lab power supply to 5V and GND and set the current limit to maybe 40 mA and see if it hits the limit.

razor85

Dec 23, 2018

	antime said:

Ok, with the cartridge plugged in, Linux recognized FTDI. Looks like the problem might be the memory chips then? They are only writeable from saturn (I mean, it can't be done through USB), right?

I don't have a lab power supply (I might find one after the holidays), so I can't really test the current right now. But I burned the arflash disk and it doesn't recognize the chips (I tried moving the cartridge and reposition it all around, still does nothing).

		antime	Dec 23, 2018
		Since you're not burning the Saturn's fuse, and it seems to start normally with the cartridge inserted, there's almost certainly no short circuit. If arflasher doesn't recognize the chips, then there may be a problem with the chips themselves, or the interface logic ICs. Double- and triple-check all joints, make sure all chips are soldered the right way around. I'm assuming you picked flash devices that are actually supported by arflasher?

		razor85	Dec 23, 2018
		Yeah, I ordered the components from mouser (the ones on your page) EDIT: Also, my first cartridge worked (until the ftdi exploded)

		razor85	Dec 23, 2018
		By the way antime, what tool chain are you using to compile the tools? I'm trying to make a version of the tools that ignore identification (and tries to write directly to my hardware) but the generated iso doesn't work in the console

		antime	Dec 23, 2018
		A self-built vanilla sh-elf toolchain.

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