usb audio multiplexer

Posted on Feb 7, 2014

As you can see, the audio ground completely isolated from digital  ground. And I`m using top copper layer as a shield for both, audio and digital ground. This helps to isolate audio part from picking up noise from digital circuitry and other EMI. Relay connected not straight to MCU pin, but it is connected through R3 and C2. It`s made for lowering relay power consumption from 28mA to

usb audio multiplexer
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about 12mA. I wrote about this trick in my article: Using Relays (Tips & Tricks). This might be helpful when this device is connected through usb-hub full of devices, when even ~15mA can make a difference. But it is not necessary implement this. Pin PB3 of MCU connected to CBUS3 pin of FT232R with 10k pull-up resistor, which can be used for power saving functions, or it can be used for providing clock to ATmega13A. You can change functions of CBUS pins of FT232R using FT_Prog software which you can download from FTDI website At first I wanted to make single-sided board, but eventually I`ve end up with double-sided one. Because of that the USB connector stayed on the bottom of the board and audio connectors on the top. But if you want you can easily change that fact. If you can`t find the exact relay I`ve used in this design, you can use any DPDT (2 Form C) 5VDC signal relay which not exeeds ATtiny13 maximum pin current. And for different relay you might need to change R3 and C2 values (if you don`t care about saving a couple of dozen of milliamps, just put jumper in there). For this simple task I was looking for cheap microcontoller(preferably from Atmel of Microchip) with minimal number of pins and with hardware UART. But the smallest and cheapest thing I found was the PIC16F688T from Microchip. Well, I guess 14 pins is too much for this task, so I`ve ended up using ATtiny13A, which, btw I had in my junk box. I just...

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