Soft Power Switch

The Soft Power Switch from Sparkfun is a unique, hard on/off switch with software control and feedback. This passive switch is similar to the power button on a laptop, allowing you to turn on and off your system with a simple press. It's an ideal choice for projects that incorporate an enclosed battery and require a reliable power button.

The Soft Power Switch features a Sense/Control pin that can serve as an output to a microcontroller, indicating the state of the power button. This information can be used to initiate a shutdown before power is lost. Alternatively, the Sense/Control pin can be driven low by the system to force a power off via software. The Fast Off pin can be used for an immediate power down.

Common usage scenarios include a microcontroller running code and checking if the power button is pressed for a certain amount of time. If it's just a quick tap, the system goes back to sleep. If the button is pressed longer, the system powers up and runs the normal program. Later, if the user presses the power button during the normal program, the same process applies. The wake-up and power-down times can be adjusted to suit your user experience.

The Soft Power Switch also supports battery charging. If the target device has onboard LiPo charging, current can be passed back through the cut-off circuit to charge the battery. The switch can handle up to 12V and includes a 3.3V clamping diode to prevent over-voltage exposure.

Despite its excellent design, there are a few considerations to keep in mind. The 22uF cap used in the switch requires an override time of 13 seconds, which can be a long wait if the system locks up. However, under normal operation, the system will power down as quickly as you define in the code, so users will rarely experience this. There have also been a few instances where the override cut-off occurs only after the button is held for more than 13 seconds and then released. This is caused by shorting between the finger on the button and the nearby capacitor. Using an external button allows the unit to power down correctly every time.

In terms of benefits, the Soft Power Switch boasts a very low quiescent current of less than 50nA and a hard override power down in case your microcontroller malfunctions. The Sense/Control pin can be connected to a microcontroller, adding to its versatility. However, it's important to note that the switch is limited to 4A and cannot handle AC loads.

The Soft Power Switch is a part of Sparkfun's rapidly produced SparkX products, designed to bring you the most cutting edge technology as it becomes available. These products are tested but come with no guarantees, and live technical support is not available for SparkX products. So, grab them while they’re hot!

For additional support or to ask a question, head on over to the Sparkfun forum. You can also access the example sketch, schematic, eagle files, and hardware repo for the Soft Power Switch.