ESP-S3 Uart

[Douglas-EDM]

Hi,
I'm using the We are using a ESP32-S3-DEVKITC-1-N8 with the uart connected to a SIM7600E.

uart.png (38.56 KiB) Viewed 6045 times

I can see the TX from the ESP on the RXD of the SIM7600, but we see a signal on the ESP RX as follow:

uart.png (38.56 KiB) Viewed 6045 times

The min is 2.84V.
I'm using Arduino IDE 1.8.19 with the following code for sending an AT command:

Code: Select all

HardwareSerial Sender(2);  
void setup() {
Sender.begin(115200 , SERIAL_8N1, 44, 43); 
}
void loop() {
Sender.write("AT");
.
.
.}

I can see that the GSM module is on and working as the light is flashing as should, I believe the problem is tat something is keeping the RX to a minimum of 2.84V instead of pulling it to 0V.

Thank you in advance for any help.

[ESP_Sprite]

You have a voltage divider and level shifter in that schematic as if the ESP32-S3 were an 1.8V part. The ESP32-S3 is not an 1.8V part, so I'm scratching my head on why those components are there. Is the SIM7600 1.8V and you accidentally put the level shifting logic in backwards?

[Douglas-EDM]

Hi, I apologize for the unclear schematics. The IC on the right is the SIM7600.
The SIM7600's UART is 1.8V.
For the TX of the sim7600 to the RX of the ESP we used the voltage level shifter as per the SIM7600 datasheet:

lvl shift.png (25.38 KiB) Viewed 5997 times

The problem is that the low bits to the ESP only pulls down to 2.8V instead of 0V while the high bits are at 3.3V as it should.
We had a previous issue as well where GPIO0 didn't pull down to 0V but instead remained at 2.8V while setup as in input (we haven't resolved that yet as we could use another pin).

[ESP_Sprite]

What pins/GPIOs on the ESP32 are you using for Tx and Rx?

[Douglas-EDM]

We are using pin 43 and 44, the two marked for U0RXD and U0TXD. They are also marked TX and RX on the dev kit.

[ESP_Sprite]

Ah. The issue likely is that those pins are connected to the USB-serial converter on the devboard, and that is hard-pulling up your Rx line to 3.3V. Suggest you use different pins and a separate UART. The ESP series generally allow you to run an UART on any available GPIO pin: you can tell the Arduino driver which one you like by calling

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Serial2.begin(baud-rate, protocol, RX_pin, TX_pin);

[Douglas-EDM]

Thank you,

We have moved the pins and it worked, we just wondered why that specific pins didn't work as it should.