A Simple Charge Indicator Circuit


Most modern phones, tablets, and computers lack color indicator LEDs for visually conveying the device’s current charge status. While some devices might have an LED for signaling the presence of AC power, they fail to change color and inform you when the battery has been fully charged.

One way of telling whether a device is done charging is to take the temperature of the charger. Generally speaking: warm/hot charger = charging; cool/cold charger = charging is complete. Rather than using your hand to sample this charge state, you can combine a couple of littleBits modules together and create a circuit for monitoring your charger temperature.

Bits Needed

Power (Space Kit)
Wire (Space Kit)
Temperature Sensor (Smart Home Kit)
Number (Space Kit)

Assemble the Bits together like this:

Power+Wire+Temperature Sensor+Number

The Temperature Sensor is held tightly against the charger with a rubber band. Use one or more Wire modules to connect the Power to the sensor. Ideally, the Power’s 9V battery should rest on your desktop and not dangle from the sensor.

Adjust the sensor to your preferred temperature unit of measure (e.g., degrees Fahrenheit), set the Number Bit to “values,” snap it in place, and turn on the power.

Initially, the Number module will display your room’s ambient temperature (e.g., 72 degrees). Slowly the temperature will rise as the charger begins recharging your battery. Don’t be too alarmed if you see temps in the low nineties.

When your battery has been fully recharged the temp display should return to your room’s ambient temperature.


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