I did continuity tests before applying power- checked 3V3 against ground, 5V0 against ground, 9Vin against ground, all came out good (0L on meter)
Applied power (9VDC wall wart), had 5V0 at the arduino's input, but 0.00 at the 3V3 line. I smell the familiar electrical smell, disconnect power (I thought about adding a fuse, but didn't have a fuse holder handy...bad juju). Flip it over, and the output lead for the 3V3 regulator is HOT. Flip it back over, and touch both regulators- both are HOT. I only had power on for 15-20 seconds, if that long.
All the 3V3 regulator powers are the 2 sensors and the level shifter (low side), and that's it. The 5V regulator powers the Arduino, Real Time Clock, and level shifter (high side).
There's no shorts of 3V3 to ground, It would be obvious to me if there were, because there's only 3 things coming off that wire.
There's 4 things coming off the 5V0 line, no shorts there as well.
I've verified polarity of the sensors, arduino, and RTC.
So what did I do wrong?
The wire against the long edge of the board is 3V3 supply
The middle wire is ground
The wire closest to the middle of the board is 5V0
The wire up the short edge of the board is ground
The regulator closest to the corner is 5V0
The more inboard regulator is 3V3
The ground wire and the capacitor terminal coming off the 5V0 regulator are NOT touching.
Yes I know my soldering skill suck, but I'm a relative newb to this stuff
White wires off sensors are SDA, green are SCL. SDA is red from the level shifter to the I2C high connection point, SCL is black. I haven't put the green SCL for the real time clock.
Green wire with red heat-shrink is the reset wire for the arduino
The small green wire making a U is the serial connection for the bluetooth (other pin is directly connected)
Red wire off the top sensor is Frequency out of the HH10D
Both Regulators are wired per the datasheet (0.1uF across the input, one has 10uF across Vout and ground, other has 22uF across Vout and ground), ground are connected together then fed to the ground bus.
When I had forgotten to connect ground but applied power with no loads, I had 9V through the 3V3 regulator, 7V through the 5V0 regulator, if that matters any.