I want to use max3232 IC with ESP32 to connect Topway HMI display. I decided to use ESP32's RX2 and TX2 pins to connect max3232. So I've tried to make this circuit (from here) for my PCB. But converter on my PCB not responding. If I use same code with third party converter (like this) codes working, no problem. Where I am making mistake, why my max3232 PCB design converter not working with my ESP32.

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my schmatic is this. I use only 100nF (0.1uF) capacitor for everywhere. 3.3 volt i am using for VCC and I have tried those 3 max3232 converter MAX3232ESE+T , MAX3232CSE+T , MAX3232EIDR

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and this is the HMI Connections

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this is Max3232 diagram

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this is my code for using serial 2 at ESP32

 // TOPWAY Smart LCD interface with Arduino
byte temp_l = 0;
#include <HardwareSerial.h>
HardwareSerial ss(2);

void setup() {
  ss.begin(9600, SERIAL_8N1, 16, 17);

void loop() {

  ss.write(0xaa); // packet head
  ss.write(0x3d); // VP_N16 write command
  ss.write(0x00); // VP_N16 address
  ss.write(0x00); // VP_N16 data high byte
  ss.write(temp_l); // VP_N16 data low byte
  ss.write(0xcc);       // packet tail
  ss.write(0x33);       // packet tail
  ss.write(0xc3);       // packet tail
  ss.write(0x3c);       // packet tail

  delay(1000);  Serial.println("yazma tamam");

1 Answer 1


You have a problem with connecting the right capacitor polarity.

Only C4 has the right polarity and you must reverse the others.

A good thing to do is to check the voltage on pins 2 and 6 (V+ and V-) to make sure the MAX232 is operating as requested.

  • \$\begingroup\$ well I am using smd capacitor without polarity. there will be an error on schmatic but it can be ignored. \$\endgroup\$
    – mehmet
    Commented Jun 18, 2022 at 4:50
  • 2
    \$\begingroup\$ @mehmet So, your schematics does not correspond to your setup, you have two completely different K1 pinouts, you did not specify VCC voltage (which defines capacitor values) and you expecting people to be able to help you? Good luck with that. \$\endgroup\$
    – Maple
    Commented Jun 18, 2022 at 4:58
  • \$\begingroup\$ @Maple 3.3 volt i am using for VCC \$\endgroup\$
    – mehmet
    Commented Jun 18, 2022 at 6:04

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