-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Somebody in the thread at some point said:
| I have no clue why the capacitor is needed (or why it's needed at all), but | for me it works great without it. Maybe it is handled already inside the IC? | Is this possible? This is basically the "DC coupling" scheme supported by the Wolfson chip, but in their version they issue a reference voltage that is half of full scale to be used instead of 0V. This is done so that minimal current is taken for silence or quiet sound... in 16-bit signed the digital 0 level is "in the middle", so 50% of DC range. When you have a capacitor in series, it blocks this constant DC and "just passes on the changes", so no current flows at all through the transducer when the thing outputs "digital 0 sample level". Again if you use the 50% level as the reference no current flows when the output is at rest at the 50% level either, both sides of the transducer are at the same voltage. But the way you're doing it the transducer is constantly passing a fair amount of static power since at "silence" it is continuously ~1.5V on one side of the 32R transducer and 0V at the other. Only when we drive - -32768 sample do we pass the minimum current, but probably still something. It's possible to disable the outputs in the driver, but it's not simple figuring out when they're really not in use since the analogue paths can drive them too for the telephony action. | It would be great if there were no objections. Then everybody could do the | HW fix for the sound issue, even without soldering skills and without | risking damage. It "works" but with the drawback explained above. - -Andy -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org iEYEARECAAYFAkkt3KIACgkQOjLpvpq7dMofUwCbBfWa61Bb6+eLCxZp4pIK+Ar5 JcwAn2PL7yLbuKzJmN5B+9/hqr/nk9uZ =S87u -----END PGP SIGNATURE----- _______________________________________________ hardware mailing list hardware@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/hardware
