5V flow rate not supported by control board without modifications

[hallboyone]

The control board was designed for 3.3V flow sensors. Turns out, they are almost exclusively 5V. To get around this with the current design, a jumper has to be soldered on and a voltage divider used to drop the 5V signal down to 3V. This should be updated in the next version of the board so no jumpers are needed. This is also related to issue #8 discussing cleaning the power to the flow sensor.