SIO2PC and external power

[+DjayBee]

Hi,

 

I am trying to connect my Atarimax SIO2PC to external power because IMO the 600XL is a too big power supply when using ProSystem.

 

I meanwhile have tried several ways by using a real power supply or the PC's USB power. Both with a 2940 voltage regulator and the USB power also without.

 

At first it seems to work but as soon as I plug the SIO cable into my 1050 the TX diode lights up and ProSystem does not recognize the drive.

 

Whe using the Atari as power supply everything works fine.

 

Does anyone have an idea on how to make this work or does everybody (ab)use Ataris as a power supply?

 

TIA

[machf]

Well... the power lines (+5V, GND) should all have a common reference (in this case, the GND signal), otherwise you'll have "floating" voltages. But the external +5V line better shouldn't be connected to the +5V line from the SIO port, nor to the PC, either... it isn't a good idea to have different voltage sources connected together. (Well, you usually connect batteries in parallel to get more current, but this is a slightly different case)

[Rybags]

Just guessing here but you'd probably want seperate grounds for the power and data, which might not be possible unless you modify the APE interface itself.

[machf]

Right, that's another thing I forgot, having separate signal and power grounds... good that you pointed it out. An examination of the whole circuit should help determine if it's possible to do it in a simple way or not.

[1050]

At first it seems to work but as soon as I plug the SIO cable into my 1050 the TX diode lights up and ProSystem does not recognize the drive.

 

In general, plugging in or for that matter unplugging a SIO cable while the system is on, is frowned upon most seriously. You may get away with doing that for a while but eventually you will loose a 1050 or ??? in the SIO daisy chain. Stop doing that immediately. If I misread your post and you are not doing that then my apologies - please disregard.

 

The only accepted method of powering your externally powered SIO2PC cable would then be to turn on the main power to all power supplys at once and cut the power in the same manner. Switched power strips work great for this considering all the Atari wall warts I need to hit with power at the same time.

 

There is a larger power supply that outputs 1.5 amps at 5 volts instead of just 1 amp - get one and use it.

 

machf points out a main concern of not having positive voltages from outside sources coming into the SIO system. This is why the 1050's power supply comes from 9 volt AC so that it "floats" on the SIO cable and can't cause troubles with any other 1050 or SIO device hooked up.

 

I'm not familar with a 2940 voltage regulator but a far more important aspect would the basic design of your custom power supply, for now I'll just assume the 2940 can deliver a rock solid +5 volts under all conditions possible.

[+DjayBee]

Thanks all.

 

I meanwhile tried it with a 9V battery running through the voltage regulator - with the same non-working result.

 

The interface itself has external GND and GND from the Atari connected together by design. Ass well as the spare room for the voltage regulator. I have not verified if the the serial port's GND on the SIO2PC is connected to the other GNDs but guess that it is.

 

On the 2940: It is similar to a 7805 but has only a voltage drop of approx. 0.5V which I needed for my first idea of using the PC's USB for power.

[Rybags]

Looking at some schematics here, I'm thinking maybe it's a case of taking away the capacitor that's normally between GND and +5 volts from the A8.

 

But really, you should be asking someone like Metalguy.