Servo - December 2013

Pololu's device is a solid-state power switch controlled by a momentary pushbutton switch. Tap the button and the switch turns on. Tap it again and the switch turns off. There's nothing unusual about that. Where it gets interesting is that it also has an input pin that can be controlled from your robot's CPU. When a high signal is applied to this pin (labeled "OFF"), the switch turns off. Wiring is extremely simple. Just connect the OFF input to an output pin on your robot's CPU.

Typical Application

There are lots of applications where you might want to automatically power-off your electronics. For this article, we added auto power-off to an existing Arduino-based wireless remote control. The application keeps track of changes to the buttons and joysticks on the remote control. If there's been no changes after a few minutes, then the application will power-off the remote. There are two versions of the power switch. One is for input voltages in the range 2. 5-7 volts and the other is for 4. 5-20 volts. Both support a maximum current of 10 amps. The 4. 5-20 volt version should be used with an Arduino. The switch only works for DC since the circuit uses a unidirectional MOSFET to control the current. You must make sure to properly connect the input source polarity. The software is simple and shown in Listing 1. The logic is simple: • Every time there's a change to a button or joystick value on the remote, reset a two minute timer.

Many electronic items — like computers, tablets, and cell phones — have a power-saving feature that puts the device into a low power state. I've frequently thought that this would be a cool feature to have in my electronics and robot designs; it can be really frustrating when I forget to turn the power off and the battery dies. Fortunately, Pololu makes a nifty little solid-state switch that exactly fits this requirement.