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Originally Posted by Listen2this1 /img/forum/go_quote.gif
I have used the Sutherland Director Pre-amp before and it works perfect. The chance of me having two sources at a time is slim, so that would not be a problem. The thing that I would like to have is a switcher like a Darwin SS from Twisted Pear that would auto switch. I am wanting to do this because of the simplicity of the systems that I could design (less knobs). I think that three inputs would be fine.
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If you're interested in waiting a few months while I do the dev work on this, I might have something that would do exactly what you want.
As I said, the design is specifically tailored for SPDIF sources, but it will be very flexible and could definitely be wired directly to a Darwin selector relay board. I expect to support 4 inputs (possibly 8, but this would make things considerably more complicated).
The basic design is to use a trimpot to set a comparator reference voltage on an ATtiny44 microcontroller. The ADC inputs (there are 8 total, 5 usable in my design) would then be connected directly to the source signals. The comparator can be switched between any of the 8 ADC inputs, and it can be set up to trigger an interrupt when the input voltage 'crosses' the threshold voltage, or it may be better to simply poll it. Either way, it should be easy to detect a signal. The microcontroller will continually scan the state of all the inputs so it will always know which ones are connected.
The AVR will be pretty much the only required part; in this case the output of the system would be 2 address lines giving the selected input and a 'signal present' signal. I2C as well. Input would be a single pushbutton.
However, I would like to make this nicer to use in a real application, so I will be adding an 8-bit IO expander intended to drive LEDs; either 2 LEDs per channel (signal/selected) or 1 bi-colour LED per channel. There will also be an analog multiplexer that would be able to directly switch SPDIF signals without relays - this could be wired 'in reverse' to drive relays as well (you would connect the output to power, and the selected input would power the relay). These parts would be optional.
Should be a pretty easy build, the tough bit would be programming the micro. Basic parts cost should be under $10, fully populated for switching SPDIF or driving relays directly. We'll see if I take the plunge to order prototype boards and build it up...
