Power Supply for ALFAT SDR @ 3.3v

File-System Hardware
1

Hi,
We would like to use ALFAT SDR by SPI to interface an SD Card.
Our MCU works with a voltage of 3.3v.
After the acquisition done, we would like to retrieve the data on the SD card through an usb cable connected to a PC (client mode).
In the documentation, we see on pin 18, the power supply should be 5v, and on pin 13, Internal vcc @ 3.3v.
Do you think that it is possible to supply this board by the pin 13 with a voltage of 3.3v given by the MCU board ?
Is it possible to have the schematics of this board in pdf format ?

Thanks in advance.
Best regards
NA

2

You can remove the 3.3v regulator and then use the 3.3v pin. You can try to keep it on there as well. If it didn’t heat up then you are fine.

Keep in mind that you need 5v for the usb host, but not for the sd card.

3

Thanks for this information.
with this modification, should it still work in client mode (connected from a PC) ?
Is it possible to have the schematic of this board (SDR ) ?
Thanks

4

@ NA - good question. I will request the schematics.

5

@ Gus @ NA - http://www.ghielectronics.com/downloads/schematic/ALFAT-SDR_Board_SCH.pdf

6

Thanks for the schematic.
When looking to it, I 'm still not sure that this board could work in client mode since Vbus is not connected inside the board (as described in the schematic).
If the MCU is not powered and I wanted to get back my data from last acquisition sequence, the board will not be powered at all since Vbus is not connected. That’s the only I could after analysing the schematic.

Thanks for your reply

7

I agree that there is no clear rename of the VBUS net to the “+5v” net that I at first assume it becomes - it is only shown as connected to pin 1 of JP1. It is however the only point on the board (other than pin 18 on JP2) that a 5v source can come from, so the question is whether that is connected at all or not - a simple powered off continuity test from these two pins should answer that question if you have a physical board in your hands. Perhaps the intent here was that if you want to run in client mode, you’ll use a jumper from the VBUS JP1-1 pin over to JP2-18.