ESP32 TTGO T-Call connect to SX1276

Question

I have an ESP32 TTGO T-Call and I want to add a LoRa SX1276. I am new to that and I am trying to write a simple program that, when it receives a packet from a LoRa sender, sends via gsm an HTTP request. GSM communication works fine with the TinyGSM library. My problem is the LoRa connection.

Specific chips according to this issue have some reserved pins. If I use the pins of the above example lora works but GSM does not work, because of the reserved pins for the SIM800. I am posting a piece of code with the LoRa setup that is not working. If there is a need for further explanation please ask. I will appreciate any kind of help.

#define SCK 14
#define SS 15
#define MISO 19
#define MOSI 27
#define RST 34
#define DIO0 33

SPI.begin(SCK, MISO, MOSI, SS);
//setup LoRa transceiver module
LoRa.setPins(SS, RST, DIO0);

while (!LoRa.begin(866E6)) {
    SerialMonitor.println(".");
    delay(500);
}
SerialMonitor.println("LoRa Initializing OK!");

Edited

With setting

#define LORA_MISO 19
#define LORA_MOSI 27
#define LORA_SCK 5
#define LORA_SS 18

#define LORA_RST 14
#define LORA_DIO0 26

Lora works (not sim800) but with the settings of @Juraj comment i am getting

E (11571) gpio: GPIO can only be used as input mode [ 11575][E][esp32-hal-gpio.c:130] __pinMode(): GPIO config failed E (11571) gpio: gpio_set_level(226): GPIO output gpio_num error E (11586) gpio: gpio_set_level(226): GPIO output gpio_num error

Edit

Although the error exists it is working with the above settings:

#define LORA_MISO 2
#define LORA_MOSI 13
#define LORA_SCK 14
#define LORA_SS 15

#define LORA_RST 34
#define LORA_DIO0 25

Some packets from the sender are lost but it seems to be working. I don't know why, but it is working... Also it does not seem very stable.

Finally pins 34-39 can be used as input so #define LORA_RST 34 is not working. But it is not receiving yet from the sender.

Answer 1

The issue seems to be arising from the pin definitions and the fact that the SIM800 and the SX1276 LoRa chip on the board might be competing for the same pins, causing interference

First, let's understand the TTGO T-Call pin mapping for SIM800:

SIM800L IP5306 version 20190610:

1. 4: SIM800L RST
2. 23: SIM800L DTR
3. 26: SIM800L PWR
4. 27: SIM800L TX
5. 32: SIM800L RX
6. 33: SIM800L RI

From the pins you've listed for the LoRa SX1276:

1. SCK: 14
2. SS: 15
3. MISO: 19
4. MOSI: 27
5. RST: 34
6. DIO0: 33

It's clear that MOSI on 27 and DIO0 on 33 interfere with SIM800L's pins.

You need to select pins for LoRa that do not interfere with the SIM800L. However, keep in mind that the ESP32 has certain pins that are not suitable for all types of connections.

a proposed remapping would be as follows:

#define SCK 14
#define SS 15
#define MISO 19
#define MOSI 22
#define RST 34
#define DIO0 25

Tell me if this works.