SpritesMind.Net

[KanedaFr]

(re) reading post about ECart, HDrive and SD cart on MCD port, a question poped up :

how much power a homemade card could use from the MD ?
I mean, if I connect something on the MCD Port, ext3 port or cart port , it's using the +5V from the MD, but how much without using external AC ?
A backup system like the SMD for ex, isn't using the 5V from MD cart port but an external AC adapter...

My MD1 AC adapt output 10V at 1.2A....I'm pretty sure Sega used this value because it's what MD needed...If I connect a harddrive which use the 5V from the MCD port, perhaps I'm stealing the power from the MD and things will start to stop working...

If I remembered my electronic course, you had to compute the Watts needed...but how could I compute the watts from the entire MD sys + my own stuff ?

(sorry if it's not clear enought but electronic course is far far away!)

[Chilly Willy]

You know what your power adapter supplies, so measure the amperage at the power plug. If you get something like 1.0A, you know you have 10V*0.2A or 2W of power left after the MD consumes its own wattage.

I imagine there's enough power to run something low-power, like an SD card, but not nearly enough to run something like a hard drive.

[HardWareMan]

When in doubt, just powered MegaDrive from your extansion PCB, and your PCB from a good power supply unit. It's right only for extension port, which has 9V input. Do not do it for cartrige slot.

[KanedaFr]

I popup this thread because I'm back on this again (working on SMD stuff)

From what i understood, I could find the real power (W) needed by a standard Genny.
If I want to add some hardware on exp or cart slot, I need to be sure it won't use more than (1.2A - measured amp).
If it needs more power (more amp or more volt), i could power it with a external AC

And here comes my new problem :
If I have the Genny using 5V XXma on cart slot and a hardware using 9V xxma how could I connect them without shortcuts ?

I never worked (on electronic course) on 2 systems talking together with 2 separate AC source...
I think you have to be sure they only share data throught data bus, right ?
The GND and VCC should never be in common.
But if Genny send data on TTL, it would be 5V for 1 and 0V for 0.
If I receive this data on my self power device, it will receive 5V from the Genny (on the Input port) and will send (9/5/3.3)V on the output port.

For ex, if I take a SMD floppy drive

signals send on the floppy port are coming from the SMD (so from the Genny) while the floppy itself is powerd by its own AC since it needs a full 1A for some operation.
The input are from the Genny and the output from the floppy drive.

I think I'm missing some points on what it TTL etc... but I don't see how 2 self powered device could exchange data safetly ...


Sorry for this perhaps dumb/newbie question but I don't know which keywords use on google to find my answer....

[TmEE co.(TM)]

answer is goood strong ground contact between the 2 devices. IF you don't have grounds connected then the devices got no reference level...
think of this as touching the input of your amplifier or when you plug in an RCA you get a loud crack, but only when there is no ground. As soon as you touch ground or the plug connects ground on the amp, then bussing or cracking will stop.
I hope this made sense
_________________
Mida sa loed ? Nagunii aru ei saa

[KanedaFr]

EDIT2: It seems the answer is the 74xx245 Octal bus transceiver, perfect for data bus

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EDIT: after some hours googling, it seems my question is more
How could I protect each IO against overvoltage, undervoltage, and overcurrent ? and do I really need it ?

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Old post for reference

Another example if the infamous RS232 : if you want to connect TTL signal with PC throught serial you have to fight between 5V and 12V signals.
To make it works you need to use something like a MAX232.
It's what the MAX232 really do to protect again a 12V "attack" that interest me....
The PC is powered by its own, the device you connect to the PC is also powered by its own (at any volt) but there is no problem.
I'm missing the basic point on how you avoid the problem when the 2 talks together.....

Do I need to isolate the signals like this
http://www.ermicro.com/blog/wp-content/uploads/2008/12/trsw11.jpg

Or use relay ?

Or use transistors ?

or octal bus transceiver ?

or any of these methods : http://www.savagecircuits.com/mixedvoltage
(applied to 5V to xV)

[LocalH]