5V power supply on STM32L475 Discovery kit IoT node

Mbed OS
1

How can I transfer the 5V power supply of the STM32L475 Discovery kit IoT node through the SX1272MB2DAS schield into the Grove UART connector. Currently in the standard formation it is transferring 3.3V, but I need 5V for the external sensor which I am trying to read out.

2

Hi,
according to schematics, the 5V is only on pin but is not used anywhere on the board. The Vdd of Grove Uart is connected to Vdd_ana and it is connected to 3,3V, also solder bridges are not present.

What a sensor you want to connect?

BTW forum also have section for hardware

BR, Jan

3

Hello Jan,

thx for answering. I am connecting a Wyler Zerotronic inclinometer:

The Inclinometer is connected to a proprietary PCB which communicates via UART with the Lora Shield/MCU. But the Wyler sensor requires 5 V for it’s internal electronics. I am thinking of supplying the 5V externally, but will the TTL via UART then still work?

4

Theoretically yes but first check the datasheet of STM32L45 for sure, but all pins are usually 5v tolerant, I think. Alternatively you can try to use a voltage divider for TX pin of sensor.

5

Voltage divider on the sensor? I don’t have access to the internal electronics of the sensor.

Will the Tx/Rx TTL communication with the proprietary board work if I supply 5 V to it from outside the shield? Surely if I were to suuply the proprietary board with external 5V, the sensor will then conduct the TTL communicatation with the SX1272MB2DAS shield on 5V?

6

There is not problem with external power supply.
When you use 5V from a external source (a battery pack, a laboratory power source) for the sensor, instead of 5v from your board, you need connect all GROUNDs together.

But different voltage level logic of Uarts can be an issue.
About different voltage logic level I found these pages Logic Levels and How to interface a 3.3V output to a 5V input and from ST page 20.
Also in the datasheet of STM32L475XX on page 61 are pins market with FT(Five-volts Tolerant) with additional sufix _a (FT_a - 5 V tolerant I/O, with Analog switch function supplied by VDDA).

I suggested voltage divider for sensor’s TX, between sensor’s TX 5V and board’s RX 3.3V, not inside.

BR, Jan