Using Multiple Power Sources

[lobstericus]

Dear Olimex,

    I received a revision C Olimexino board which has the USB connector and the screw terminals
(no barrel jack). I had a few questions about the board:

1) Is it safe to connect the usb (with power from a computer host) and a second voltage source
   to the screw terminals at the same time? (It looks like there is a first stage regulator
   that accepts VIN and produces 5V for an internal rail that supplies secondary 3.3V regulators.
   Will the first stage regulator conflict with the USB which I gather connects directly to the 5V rail?
   I will need an external supply but would like to leave the USB attached for programming. Unlike the
   maple, there are no power jumpers to select this.

2) I gather the first stage regulator needs > 5 V to produce a reliable 5V rail internally used for
   the 3.3V second stage regulators so +5V on the screw terminals will not work?
   Would it might be possible to run the Olimexino off 5V supply by using the 5V pin on the usb connector?

3) Is it possible to access GPIO pins beyond D37?  (I'm told Maple has 38-42 broken out to through holes
   but not on headers? ).


Regards,

B.

[LubOlimex]

Hello lobstericus,

1) It is ok to have both power jack and mini USB plugged at the same time.
2) The board is powered ok by the USB, but some features are turned off - like battery charging, also not reliable for powering additional modules on the UEXT.
3) It is possible to get more GPIO pins if you disconnect a peripheral. For example if you don't use both LEDs you can disconnect one of them and use its pin as GPIO. Another example would be disconnecting the CAN interface and using its pins for GPIO. However, I don't recommend you doing so.

Best regards,
Lub/OLIMEX

[lobstericus]

Dear LubOlimex,

    Thanks for your quick reply.  From the schematic, it looked like the models with the barrel jack connector had a disconnect switch in them, so I wasn't sure simultaneous connection was supported for the screw terminal model which wouldn't have the disconnect. I was concerned that if I have two 5V regulated supplies (the host computer's through USB) and the Olimexino's own internal 5V regulator that they might both try to pull the voltage to slightly different levels - say 5.1 V and 4.9 V.  I gather from your response that this will not be a significant problem.

Regards L.