I have two modem HATs.
HAT B is one of these: https://www.waveshare.com/product/modules/wireless/gps-gsm/gsm-gprs-gnss-hat.htm
Using both a Pi model B+ and a Pi Zero, I can successfully power on HAT A at boot by the addition of these commands to /etc/rc.local :
echo 17 > /sys/class/gpio/export echo out > /sys/class/gpio/gpio17/direction echo 1 > /sys/class/gpio/gpio17/value
HAT B does not power on automatically with these commands.
I've found the schematic for HAT B here: https://www.waveshare.com/w/upload/2/20/GSM-GPRS-GNSS-HAT-Schematic_.pdf.
Looking at the section in the middle at the bottom of the schematic (titled 'RPI GPIO'), it would appear that the power gpio is number 17, and so the code I have in /etc/rc.local should work (but doesn't) -- have I misunderstood the schematic? I've not dealt with gpio in the past.
Can anyone suggest a way of getting HAT B to turn on automatically at boot, please?