Soft switch sound switcher using a few 2N3904 and resistors

Having two sound sources connected to the same output may be good for a while but sometimes you don't want to have both sources outputting sound at the same time and may want to switch between them. I wanted to be able to control this with a micro controller and not use a servo, so a mechanical switch is out of the question.

Transistor as switch

I know that you can use transistor as soft switches so I started researching how to build this.

Power Small FINISHED projects from USB

Often I create a small... thing, not really anything to write home about but something that blinks a LED for example and I use and Arduino to power it. This is good for the building stages but using and Arduino just for the 5V output is not efficient.
So I wanted a way to power the devices from USB 5V. this is bad for the laptop health if the project is not finished and there are still problems with the wiring but when all is finished, you can safely source the needed voltage from a PC (remember no more than 500 ma).
My solution is a power cable with a USB male on one end and standard header pins on the other.

Small UPS for RaspberryPi

Some time ago I went into Radio Shack and found a small USB rechargeable battery that has a retractable USB connector on one end and a microUSB on the other. It looks something like this but it is only 800 mah and was on sale for $8.

I wanted to use it as a power source for my RaspberryPi but wanted it to use the battery only when mains where off. I looked around for circuits that allowed for instant swithcing between 2 power sources and actually found something I could make but it was pretty complicated.

Upgrading HP Compaq 6715s with a Motorola Surfboard SBG6580 wireless card

So after pulling apart the dead modem/router I wanted to use the only working part scavenged.

I opened my wife's laptop to access the wi-fi card. This is the easy part as it is just one screw for the panel and 2 screws that hold the wi-fi card in place.

HP Compaq 6715s back

HP Compaq 6715s panel that contains the Wi-Fi

A close up of the old WLAN card

The first problem appeared:

HP Compaq 6715s new WLAN installed

Motorola Surfboard SBG6580... to pieces and beyond

So this year did not start well for me. When I finally woke up on the 2nd of January my internet kept going down on me. After numerous restarts and resets of my wonderful modem/router combo it died. The top 3 lights would flash for a sec and then nothing. That is the last time I buy one of these all-in-ones (on a side note, don't get the Belkin wireless router it restarts every time you change any settings).

Anyway here is what I found inside it:

A main board with a mini PCI Express slot.

Front of main board

and the other side

Back of main board