I've been working on a project that uses a tinyscreen+ in combination with a thermocouple board from adafruit (MAX31855).

This TC board needs an external power source to run, and I've been trying to send voltage from the tinyscreen+ to the MAX31855 through a tinycircuits expansion shield to accomplish this, but I've been unable to get any of the pins I've tried to send voltage.

I used digitalWrite and analogWrite for pin 13, in addition to hooking up VCC and VIN pins to the VIN or 3Vo pins in several combinations (which in my experience, VIN/VCC with arduino boards usually don't require inclusion in programming to send power), and none of them sends power to the MAX31855.

Is there specificity to which pins can use the digitalWrite or analogWrite functions on a tinyscreen+ expansion shield like other arduino boards? Is VCC or VIN on the expansion shield supposed to send either 5V or 3.3V automatically? Is there another foolproof way to send voltage from a tinyscreen+ through the shield pins that I'm not aware of?

Hi- VCC is the best way to power external sensor boards. On TinyScreen+ it will output 3.3V when TinyScreen+ is switched on. You should be able to connect this to either the VIN or 3VO(bypassing the boards 3.3V regulator) on the Adafruit board, along with ground and necessary IO pins.