out of topic


 sorry why I send a post  here, but it did not show,   and  the listserver
 told,  they send   the message


 already,,   what trouble  could be?

    sorry  again,


  James  Chu



----------
> 0e%s*L: Russell McMahon <apptech@clear.net.nz>
> &,%s*L: PICLIST@MITVMA.MIT.EDU
> %D&.: Re: ISD sound chip questions
> $i4A: 1998&~4$k7$i AM 09:28
>
> >Does anyone have a circuit for electricaly coupling the
> sound output from an
> >ISD sound chip to a small, one transister FM transmitter. I
> have tried, but
> >had to settle for acoustical coupling.
> >
>
> I use USD chips extensively. Electrical coupling should be
> extremely simple. Coupling from 1 speaker output pin to the
> transmitter input with a capacitor (0.1uF probably OK)
> should be enough. The speaker outputs are differential (one
> is high when the other is low) and both are always above
> ground so you don't need to use both to get a single ground
> referenced output.
>
> Points to watch are:
>
> - Levels: is the TX happy with the ISD output level (may be
> too high or too low).
> - Grounding: ISD has separate analog and digital grounds.
> See their app notes for layout advice.
> - Ground loops: Standard audio trap. beware of having more
> than 1 ground path from one circuit to the other. This
> can/will act as a pickup for other signals. Also common
> impedances in the path to true ground shared by 2 circuit
> elements may couple ground return signals between them.
>
> >Also, any pic circuits and software for controlling an ISD
> for recording
> >sessions, perhaps from a PC?
>
> ISD have a series of application notes covering all aspects
> of their use.
> see www.isd.com
>
> >Also, any ways to copying the recordings from one ISD chip
> to another?
>
> The only way that i am aware of is at the analog level - 1
> chip is set to play back and the other records. This is not
> ideal but you do not have access to the inner workings of
> the ic.