Drum Hat Interrupts Not Detected

Hello everyone,

I am trying to use my Drum Hat with interrupts on ALERT PIN, which is connected to GPIO25 on raspberry pi (i am using RPI 2B).

The problem is that I can’t detect any interrupt on GPIO25, even when my INT bit is set in Main Control Register. I can clear INT bit and when a pad is touched, Main Control Register goes back to 0x01, but I still have no changes on GPIO25.

I checked register 0x27 about interrupt enable, and it is properly set at 0xFF. I setted back all registers with default values.

Someone have any idea to help me with these interrupts?

I’m afraid I don’t have one of these to try it, but what signal are you looking for on GPIO25? Have you checked the configuration register to see what the alert polarity is? Note that the pin descriptions suggest that you might need a pull-up resistor.

Hello Shoe, thanks for your answer

My configuration register 2 (0x44) is setted with 0x40, so I got the ALERT# pin active low and open drain.

What I have done to look at GPIO25 :

cd /sys/class/gpio
echo 25 > export
cat /gpio25/value

The value is always at 0, no matter the value of INT bit.

The suggestion of pull-up resistor is written in the CAP1188 datasheet, but I got the Pimoroni Drum Hat, which is a board already rooted and I can’t have the schematic. However, when I look at the board, I can’t find a resistor after the alert pin so …

I got it ! After I wrote the previous sentence, I did changed the config 2 register (0x44) and I setted it with 0x00. Then the alert pin is active high. This is necessary since there is no pull up resistor after the alert pin on the Drum Hat board.

Thanks again !

Romain