DISTANCE( trigger, echo ) or DISTANCE( trig-echo )
Measure the distance to a target using the HC-SR04 ultrasonic distance sensor.
Four pin sensors have separate trigger and echo connections. trigger is the I/O
pin connected to the "trig" input of the sensor and echo is the pin connected to
the "echo" output of the sensor.
Three pin sensors have a combined trigger and echo connection and in that case you only need to specify one I/O pin to interface to the sensor.
Note that the HC-SR04 is a 5V device so level shifting will be required on Pico (RP2040) processors but not on Pico 2 (RP2350) processors.
The I/O pins are automatically configured by this function and multiple sensors can be used on different I/O pins.
The value returned is the distance in centimetres to the target or -1 if no target was detected or -2 if there was an error (i.e. sensor not connected).