čtvrtek 15. srpna 2013

Qi compatible wireless charger LED tweak

Hi, I'm moving to another country soon and my current project was put on hold.
Here is just a small tweak to a wireless charging pad I got for my galaxy S4. I hated the single red LED close to the USB port. It looked hidious so here is my mod:

Removed top cover:
 I was wondering how the coil looks like
 If you notice there is one 0603 size LED placed just beside the USB connector. There is also 2 LEDs unpopulated. After connecting LEDs to the other places to see what it indicates, all I got were three flashes when powered on, so I removed the original LED and used the pads on the PCB to connect a transistor. The LED is grounded by the microcontroller and the resistor is connected to the +5V so I used a generic PNP transistor. Base to the negative pad of the original LEDgoing to controller through a 1k resistor (active when low), Emitor to the ground and collector to all cathodes. Anode of the LED is going to the 5V. Secured on place with hot glue gun.
 Single LED wired
 More LEDs just connected together
 Full wiring

 And working :)

When you plug the pad to the power supply, it will flash three times (last picture was taken during them flashes), the LEDs are switched OFF. When you place your phone onto the pad, LEDs go ON until you remove the phone.
Definitely looks better than just one single red LED in the corner.
Transistor used: general PNP transistor capable of 100mA or more
Resistors: 220ohm (My LEDs had 3.2V drop @ 20mA-> (5 - 3.2 - 0.5V VCE)/220 = 6mA each x9 LEDs = 50mA (roughly)
+1 resistor between transistor and controller. I used 1k, but look into the datasheet what current your transistor need to open fully. The 0.5V VCE is voltage drop on the transistor itself - depends on the transistor used. I might hear something regarding the calculations, like voltage drop on LED at lower current will be lower ... it's not that important.
Hope you like it :)