July 21, 2024, 11:13:37 PM

Olimexino-Nano board questions

Started by mtrifonov, April 18, 2015, 03:48:36 PM

Previous topic - Next topic

mtrifonov

Hi,

I just bought an Olimexino-Nano board and since I can't find a manual (correct me if I'm wrong) I have a few questions around the board design. Specifically about powering the board and the extra solder pads on the PCB.

1. I noticed this is a 3.3v device. Except for the +5v VBus line, all I/Os are 3.3v. Is there a way to easily convert it to 5V, same as the original Leonardo? I know UEXT specifications require 3.3v, but I won't use that (at least not with any Olimex MOD modules). What about the SDCard slot, can it handle 5v?

2. How do I power the NANO from another 3.3V device (IOs will be 3.3v of cource)? Can I use the UEXT connector pin1 or I need to run a cable to the 3.3V pin (pin 3 on the CON1 connector)?

3. What are the VBAT1/2 lines for? Looking at the schematic for the battery shield, as far as I understand, VBAT2 is input voltage from the LiPo battery. I'm not so clear on VBAT1. It looks to me that's intended for a non-rechargeable coin cell battery and the input is not regulated and connected directly to the battery. Is that correct? What type of battery should one use?

4. What are the two solder jumpers PWR/CTRL and UEXT_PWR_E for? My understanding is that out of the box I can use digital pin 8 to turn on/off the 3.3v to the UEXT connector AND the SD card (LOW=on, HIGH=off). If I want to have the SD card always on, independently on the UEXT power, I need to cut the trace (1-2) on the PWR/CTRL jumper and connect 2-3. How about if I want to have the UEXT always on and use D8 for other purposes? Connect all three traces on PWR/CTRL (1-2-3) and cut the trace on UEXT_PWR_E, correct?

Thanks

MBR

Quote from: mtrifonov on April 18, 2015, 03:48:36 PM
1. I noticed this is a 3.3 device. Except for the +5 VBus line, all I/Os are 3.3v. Is there a way to easily convert it to  5V, same as the original Leonardo?

You will need so-called "level shifter", because the I/O are not 5V tolerant. It may be done as mostly passive circuits (see http://electronics.stackexchange.com/questions/81580/step-up-3-3v-to-5v-for-digital-i-o) but I recommend the active buffer drivers like 74HC125 (quad), 74HC367 (hex), 74HC541 (octal) or such. The input ones will be powered from 3.3V side, the output ones from 5V side.

mtrifonov

Sure, but not what I meant.

As far as I remember and after double checking the datasheet, the Atmega32U4 Vcc range is 2.7V-5.5V and max rating for all I/O pins is <= Vcc + 0.5v, which means if you power it at 5v (let's say from the VBUS directly) I don't need level shifters for the I/Os, which is what I'm asking about. Can I (relatively easily) modify the board to do that? Also, considering I don't use any UEXT modules that are 3.3v (at least not without level shifting), will I have other issues, like with the SDCard? Can it work at 5v?

Also, after looking at the datasheet, I noticed something in the electrical characteristics which brings me to another question:

5. What is the NANO's operating frequency? 8MHz? Most boards with similar designs you can find run at 8MHz at 3.3v and according to the datasheet 16MHz @ 3.3v is outside the 'Safe Operation Area'.