I have designed a 5v and a 3.3v regulator getting same source of 12v battery.
When I measure, the 5v regulator output shows -4.67v for
+ on black probe and
- on red probe, and 5.12v when red is connected to
+ and black to
Similarly for 3.3v regulator...
Now I have an Arduino project and it includes a flow sensor. This project works fine if the serial port is connected to a laptop. But if I only connect an external power supply as described above, the sensor gives some output even if there is no flow.....
[The second problem involving a flow sensor has now been asked in a separate question here.]