0
\$\begingroup\$

I have a UART connection from an ESP32 (esp datasheet to a Quectel BG95 that I cannot get to work. At first I thought it was code related but after reviewing the AT manual several times. I am thinking it must be circuit related...

Here is a schematic of the connections first we go from the esp through a level shifter datasheet (3.3 to 1.8 V) then to the BG95 datasheet.

esp connection

level shifter

quectel connection

Below is the code I used, which sends an AT command with return carriage, according to the manual I should be getting an OK back.

#include <HardwareSerial.h>
int greenpower = 32;
int led = 33;
int pwr = 5;


void setup() {
  
  pinMode(pwr, OUTPUT); //for verifying power to the board
  pinMode(led, OUTPUT); //for verifying power to the board
  pinMode(greenpower, OUTPUT); //for allowing power to auxillary processes
  digitalWrite(greenpower, HIGH); //allow power to aux devices
  digitalWrite(led, HIGH);  //apply power to verification circuit
  digitalWrite(pwr, LOW);  //begin modem start-up
  delay(5000);
  digitalWrite(pwr, HIGH);  //start-up signal
  delay(750);
  //digitalWrite(pwr, LOW);  //end modem start up sequence
 
  
  delay(5000);  //wait for stabilization

  Serial.begin(115200);  // Open serial communications and wait for port to open:
  Serial2.begin(115200,SERIAL_8N1);

}

void loop() {
  Serial2.write("AT\r");
  while (!Serial2.available()) continue;
  while (Serial2.available()) {
    char g = Serial2.read();
    Serial.print(g);
  }
}

PCB footprint

Note that the level shifter is upside down. But does anyone have a clue as to what I am doing wrong here?

\$\endgroup\$
1
  • \$\begingroup\$ From the scope picture of the Rx connected to the Tx indicates a broken or open connection. Since they are connected they should be the same. I use an inexpensive china logic analyzer, it makes this a lot easier to troubleshoot. Then can be gotten to your door for under $10.oo in the USA. \$\endgroup\$
    – Gil
    Aug 7, 2021 at 3:23

1 Answer 1

1
\$\begingroup\$

Probably, you are pulling the last hair out.
Assuming everything correct you did, looking at the third scope picture..., very random thoughts:

  1. Check if that broken signal pin requires pull-up... Why would it?
  2. Ohm (continuity check) that signal pin/trace with adjacent signal traces/pins.
  3. Remove and re-solder suspected parts.
  4. Ask the assembly house or PCB manufacture to X-ray the assembled board.
\$\endgroup\$
3
  • \$\begingroup\$ Thanks for these suggestions I am updating the question with some recent findings. \$\endgroup\$
    – Feynman137
    Aug 10, 2021 at 2:25
  • 1
    \$\begingroup\$ Way to go @Feynman137 ! It looks good, \$\endgroup\$
    – jay
    Aug 10, 2021 at 12:59
  • \$\begingroup\$ Thanks man.. I am confused though I am seeing the signal on the scope but getting blanks in the serial monitor. \$\endgroup\$
    – Feynman137
    Aug 11, 2021 at 4:23

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.