The optical sensor breakout board requires a three pin connection using 5V, GND and any of the available GPIO on the Raspberry Pi.

Following is the required circuit:

With power controller circuit:

We'll solder three male header pins for connecting the breakout board. Notice the green colored solid core wire is connecting pin GPIO17 with one of the male header pins. The other two pins are connected to GND and the 5V rail.

Closeup photo of the ATO circuit. Notice the temperature circuit (for DS18B20 sensor) is located right above the ATO circuit.

It is perfectly fine to use a separate Perma-Proto board (my personal favorite is the mint tin size Perma-Proto board) if you find the Perma Proto HAT is too crowded.

That's it. Like most of the reef-pi electronics, the ATO circuit is really simple. Next, we'll go ahead and mount it along with the optical sensor breakout board in the housing.