Wireless charging device detection with photosensors

A device comprising:

• a wireless charging circuit to wirelessly charge a portable electronic device;
• and
• a presence detection circuit connected to the wireless charging circuit, the presence detection circuit comprising:
• a device-detecting photosensor positioned to sense ambient light and to be occluded by the portable electronic device when the portable electronic device is positioned at the wireless charging circuit;
• an ambient-light photosensor positioned to sense ambient light and to not be occluded by the portable electronic device when the portable electronic device is positioned at the wireless charging circuit;
• and
• a comparator to determine a difference in light intensity sensed by the device-detecting photosensor and the ambient-light photosensor, the comparator to output a signal that turns on the wireless charging circuit when the difference in light intensity exceeds a threshold difference.

A computing device comprising:

• a housing including a surface;
• a wireless charging circuit positioned within an effective range of the surface of the housing;
• photosensors positioned to sense ambient light incident at the surface of the housing, wherein the photosensors are separated by a distance;
• and
• a circuit connected to the photosensors, the circuit to detect a portable electronic device placed on the surface by determining a difference in signals outputted by the photosensors and, in response to determining the difference in the signals outputted by the photosensors, the circuit to turn on the wireless charging circuit to charge the portable electronic device.