Thing Plus C doesn't respond to GPIO interrupts

Development Boards ESP32
1

I’ve built several payload packages for high altitude balloons using Mega and Due boards as the data collection processors.

But, I’ve run out of ideas on how to get the interrupts working on this Thing Plus C board. I have a solid pulse from a 555 triggered by a geiger counter going through a voltage divider and into a GPIO pin (have tried both 15 and 12 pins). I am running a versions of this on the mega and Due and they work fine. For the ESP I changed the ISR to :

void IRAM_ATTR IncRadCount() // Interrupt Service Routine to count Geiger pulses

{

radCount ++; // Volatile variable to hold geiger pulse count

}

And attached it via:

pinMode (GEIGER_IN, INPUT);

attachInterrupt(digitalPinToInterrupt(GEIGER_IN), IncRadCount, RISING); // Set interrupt service routine

Since I have an LED on the output side of the 555 I know a solid pulse is being produced and input to the ESP32 via the voltage divider. Interrupts don’t trigger.

I’m also somewhat confused by the board selections in the Arduino IDE. The hook up guide for the Thing says to use the Adafruit ESP32 Feather. When I do, the code doesn’t work the I2C devices composed of a BMP280 and RTC. I get same result if I choose the Sparkfun Thing Plus. Using the ESP development board and ESP32 WROVER selections everything works except the interrupts. Any suggestions, or advice will be greatly appreciated.

2

Update: Changed GPIO pin to pullup and first reading seemed OK. Second pass through loop resulted in huge jump of the geiger count (1600+). All counts after were similar. Noticed in schematic from Sparkfun there were cautions about using GPIOs 0, 2,5,12,15. Although the caution didn’t seem to apply to my case I thought I’d use another GPIO pin. Switched input to GPIO27 and it seems to work. Why, I have no clue. :?: