interrupt GPIO36 and GPIO37 signal mixing/crosstaling

[smarq8]

Hardware:

Board: TTGO T-DISPLAY Core Installation version: espressif32@3.2.0 arduino framework IDE name: platformio

Description:

I have 2 interrupts from sensors, MPU6500_INT=37 and ADXL355_INT=36, the only thing I do is increment some counter for each sensor, everything were fine as I use them separately, but as I run them both at one then interrupts seems to "crosstalking" and my counters do not show me expected value. Removing wire ADXL355_INT=36 cause firing both interrupts at the exact same time. However changing ADXL355_INT to 33 or 38 fixing that trouble, and it seems something happen between GPIO36 and GPIO37. Both signal are push-pull and both pins are configured as INPUT, resistance between them is 10Mohm so its probably not "obvious" shortcircuit.

static IRAM_ATTR volatile uint32_t _interruptsN[4] = {0,0,0,0};

void IRAM_ATTR _onInterrupt0(){
    _interruptsN[0]++;
    // if(_onInterruptExt[0]) _onInterruptExt[0]();
}
void IRAM_ATTR _onInterrupt1(){
    _interruptsN[1]++;
    // if(_onInterruptExt[1]) _onInterruptExt[1]();
}

[atanisoft]

@smarq8 In most ESP32 devices that use a WROOM-32 or WROVER module GPIO 36 is connected to GPIO37 using a 270pF capacitor. GPIO 38 and 39 are the same way. You can also find the schematic for the T-Display here: https://github.com/Xinyuan-LilyGO/TTGO-T-Display/blob/master/schematic/ESP32-TFT(6-26).pdf

Very few ESP32 DevKit boards expose GPIO 37 and 38 for that reason and those that do shouldn't!

[jason-kong]

Running into something similar right now on a very simple circuit.

Using external pullup resistors and some keyswitches, the digitalRead values from GPIO36 cross talk with GPIO37, so pressing one switch claims that the other is being pressed as well (externally checking my project with a multimeter suggests it's gotta be internal to the board itself and not my parts)

I saw the capacitors @atanisoft in the schematic, could they be removed perhaps? I'm assuming they're SMT mounted on some boards (mine is a Sparkfun ESP32 thing)

[atanisoft]

They are internal to the esp32 module in most cases and can not easily be removed. In the case of the T-Display they might be removable. But I wouldn't recommend using GPIO 37 or 38 for any purpose.

[jason-kong]

They are internal to the esp32 module in most cases and can not easily be removed. In the case of the T-Display they might be removable. But I wouldn't recommend using GPIO 37 or 38 for any purpose.

Thanks for the tip, I'm running out of GPIOs on my keyboard project but I hope (pray) there's two I can swap 37 and 38 over to

[atanisoft]

You might consider moving over to the ESP32-S2 which has more IO pins and a dedicated GPIO driver that can be used for a keypad input.

[jason-kong]

Been looking into that a bit though I recall it doesn't have the BLE functionality of the plain ESP32, though the USB host could would be a great upgrade.

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