Having the RFID1356MIFARE in UART Mode and connected to the ESP32 using the UEXT connector makes the ESP32-EVB to not boot properly.
When powered on using USB the ESP has PWRLED1 and LED1 on.
When powered on using +5V the ESP has PWRLED1, PWR_GOOD1 and LED1 on.
The RFID1356MIFARE flashes both LEDs on both scenarios, like it should be.
Also, in this "mode" some GPIOs are at 3V3.
In order to make the ESP boot normally I have to hit the RST button. By booting normally I mean that the ESP executes the code that I have uploaded on it.
If I disconnect the RFID1356MIFARE from the ESP32 and then I connect the ESP to power it boots normally. Then I can connect the RFID reader in order to use it.
These are the pins that I plan to use. They are connected to nothing right now.
But since the ESP doesn't boot, it doesn't reach the code so it shouldn't care about free pins.
#define RELAY1 32
#define RELAY2 33
#define W0 14
#define W1 13
#define INPUT_1 15
#define INPUT_2 17
#define BUTTON 34
#define BUZZER 16
So, the only GPIOs that have a state at BOOT are the ones that come from the RFID reader, which should be GPIO4 and GPI36.
EDIT: I've tried with a different ESP32-EVB and it happens exactly the same.
Also, the PWR_GOOD1 led sometimes is on and sometimes is off.
I think this issue is more related to MOD-RFID1356MIFARE than it is related to ESP32-EVB. There is 10k pull resistor on MIFARE's RX line which causes the issue.
It seems like adding 1K pull down resistor between GPIO4 and GND fixes the issue. You can also find GPIO4 and GND on EXT1 row of pins. This is how I tested:
There can be other solutions but the problem is related to the pulling up of the GPIO4 during power up.
You can also try to replace R12 pull up resistor of MOD-RFID1356MIFARE with 100k (10k originally). So these are three workarounds for the problem - use another GPIO; add additional pull-down resistor on GPIO4; modify attached board with bigger pull-up resistor.
Quote from: LubOlimex on February 25, 2021, 11:41:44 amYou can also try to replace R12 pull up resistor of MOD-RFID1356MIFARE with 100k (10k originally). So these are three workarounds for the problem - use another GPIO; add additional pull-down resistor on GPIO4; modify attached board with bigger pull-up resistor.
I've replaced R12 with a 100k resistor and now the ESP32 boots normally. Not the prettiest way, but it works.
Thank you for the update, glad the issue is solved. I am sure another person would find your experience helpful.