In SX Microcontrollers, SX/B Compiler and SX-Key Tool, william wrote:

Dear pjv,

Thanks for your reply.

1.  When you say the SX is fast enough, did you mean that 1 SX52 is fast enough is run 3 pairs of conversations simultaneously? 
     i.e.  6 ADCs and 6 PWMs at the same time?
     What would be the sampling speed when handling 3 buses at the same time?  8K samples / second?

You mentioned, "one SX per line/channel", which I don't quite understand.
Are you saying I may want to use 3 SX52s for the 3 pairs of conversations?

If I do this, I would need a lot of relays to switch the Exts to the correct buses.
The reason I want to design it with only 1 SX52 is to allow software switching, no relays for switching.
Only 2 SSRs to offhook the 2 incoming trunk lines.

One more question,  should I mix the 2 ADC returned values together in software before playing the summed value out for both PWMs to reduce echo?

4. I have some experience in designing Dialers and CallShop systems.
So I know a bit on DTMF decoding, generation PSTN handling and opamp filters, but this would be the most ambitious so far.   : )

If you like, I could share 1 board with you when it is made.  I usually make 5 boards for prototypes.

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