Reverse use RPi-UEXT

[jlucius]

Hello,

I am trying to reverse use RPi-UEXT as it was ment in original design. I want to connect a module designed for the RPi on an OLinuXino A20 Board.

It seems to me that the RPi-UEXT can be used for that connecting the RPi module to the RPi-UEXT and the RPi-UEXT to the A20 using UEXT. I was hoping for a just plug-n-play, but:

The module uses I2C and only connects the pins 1 (3,3V), 2 (5V), 3 (SDA), 5 (SCL), 6 (GND) on the RPi header. According to the RPi-UEXT all signals should map to the UEXT connector, except 5V that is missing.

Has anybody a suggestion where to best get the 5V needed? Or why this should not work at all?

Thanks.

[Lurch]

The UEXT on the A20 has 1-3,3V, 2-GND, 5-SCK, 6-SDA
All of the GPIO-x 40-pin connectors have +5V on pin 1
If you device requires 5V I2C, you may need dividers or level-shifters to chenge the 3,3V to 5V
The A20 schematic is on the WiKi

[JohnS]

Be careful not to put any voltage more than about 3V into any pin on the A20.  It is NOT a 5V-tolerant chip.

Level shifters should let you avoid that.

John

[jlucius]

The module actually only needs 3,3 V I2C Signals. The 5V seems to be needed to power some of the components. I do not have any schematics on the module.

I have looked up a GPIO pin on the A20 with 5V in the schematics and took a look at the RPi-UEXT schematics, that the 5V connector on RPi-UEXT is only connected to the RPi connector pins 2 and 4 and has no connection back to the UEXT (I love Olimex for making the design files public).

So as far as I don´t accidently connect something wrong this should be fine (at least for testing purposes)? Just want to double check, not to burn my board.