I was a bit confused at the operation until they clarified.
You provide the desired voltage to switch on Vcc (e.g., 5 volt, 12 volt, ...) and the ground.
These wires should be sufficient to carry the desired load current.

You provide a switch signal (e.g., 5 volt or 3.3 volt) to the sw signal to close the switch and gnd to open the switch. The LED turns on when switch is closed.

When 5 volt or 3.3 volt are provided, the neg output connection is shorted to ground thereby completing the output circuit.

I wondered what would happen if I applied 110 volt ac. I found that a 150 watt bulb dimmed. No damage though so this product is robust.

With this board you get
1. the board
2. demo code (undocumented)
3. a schematic

It's not a complicated board. But to understand how it works I have to spend time trying to read somebody's undocumented code and then go to the schematic so that I can download the DAC data sheet so I can understand how that works. Why can't somebody from this company just spend an afternoon and write up some basic documentation?

Update-Will look forwards to the additional documentation. Product works as advertised and is very nicely executed.

I had originally bought the Arduino Due, in hopes that I could use the output voltage as a control for motor driver circuit. Not in any easy to find documentation, the Due can only go down to 0.5V and only up to 2.7V. This did not meet the requirements I needed for the motor control. I looked online for a cheap solution that was compatable with the arduino code I had already written.

Unfourtunatly, this device does not have a working code example for the Due. The Due uses different interrupts. Once I acquired an Uno, the code worked flawlessly. Thank you for having such an easy to use product. Please look into adding support for the Due. The added speed and memory allows for more robust programs.