On Jun 21, 2007, at 8:23 PM, Jinx wrote:

> I stripped some telcom boards for parts recently and got these
> in PLCC
>
> http://products.zarlink.com/product_profiles/MT8816.htm
>
> No idea what I'll use them for yet, but probably worth having

They're very useful for analog audio path switching inside Amateur  
Radio FM repeater controllers.  :-)

Mitel made some nice stuff, really.  The venerable MT8870 DTMF  
decoder is still used in an awful lot of stuff.  Mitel being gone, or  
hard to find, or whatever... (I forget), the clone of the 8870 made  
by California Microdevices (CM8870) is easier to come by.  That darn  
chip with it's variable capacitance filters will pull DTMF signals  
out of ridiculous amounts of noise, while also dealing with obscene  
amounts of both twist and skew.

Sure, DSP-based solutions can match or better it, but for ease of  
use, the 8870 is hard to beat in a discreet component.

I've seen the 8870 pull DTMF out of noisy FM radio signals that were  
well below the pseudo-industry-standard 12 dB SINAD "noisy signal"  
level.

The datasheets also have a pretty nifty description of how they do  
it, too... was fun to read while I was putting in some serious  
hobbyist study-time on op-amps and filters.

--
Nate Duehr
nate@natetech.com


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