Switch off the HDMI
With the current Debian we use it is rather easy to switch off the HSMI and thereby freeing a lot of IO-pins for other purposes. Provided you are running the Debian from a SD-card ou can follow these instructions:
First log in as root.
Next change to /boot
]$ cd /boot ]$ vi uEnv.txt
In the uEnv.txt file remove the # before the line starting with cape_disable=...:
##Disable HDMI #cape_disable=capemgr.disable_partno=BB-BONELT-HDMI,BB-BONELT-HDMIN
Save the file and reboot.
Readout the cape manager settings
[ ✗ root@mybone [~] $] cat $SLOTS 0: 54:PF--- 1: 55:PF--- 2: 56:PF--- 3: 57:PF--- 4: ff:P-O-L Bone-LT-eMMC-2G,00A0,Texas Instrument,BB-BONE-EMMC-2G 5: ff:P-O-- Bone-Black-HDMI,00A0,Texas Instrument,BB-BONELT-HDMI 6: ff:P-O-- Bone-Black-HDMIN,00A0,Texas Instrument,BB-BONELT-HDMIN
The missing L in the two lines with HDMI indicates that the Device Tree Overlay is no longer active.