I am about to use the Teensy LC for a rain-gauge using the HC-SR04 ultrasound module. This sensor is said to use circa 15mA - 20mA.
Since the gauge is to be solar-battery powered I am considering using Pin 17 (Vin) for switching the supply on/of (ca. 5V) to the HC-SR04. However, the useful info-card supplied with the Teensy LC states just 8mA.
Pin 17 (Vin) is controlled via a 74LV1T125 which can handle +/-25mA at the output. The only reference to an 8mA I find is in the “Static Characteristics” which is not a limit-value.
Has anyone any user experience or further information on Pin (17)??
I believe that pin 17 has that 5V output buffer for 5V logic, but is not ideal for sourcing current. According to the table in [this post on the PJRC Forum, you can either source 20mA @3.3V from Pin 17 or you can use the 5V buffer on the “bottom” of the board for 5V logic control. For this, it might be easier to use a transistor to control power to the HC-SR04.](Coming Soon: Teensy-LC (low cost Teensy) | Teensy Forum)
As TS-Mark said, pin 17 is used to control 5V logic level; mainly intended to drive LED pixel strips that need a higher-level control voltage. It’s not a power output.