Hi

i hope some of you remember my previous thread regarding controlling sound sources and sharing the speaker with uC speaker and a ISD chip. well i am on the point of solution and this time i need some help in circuit adjustemnts. here is the circuit '

http://www.angelfire.com/ak/shahzad73/Speaker.gif


some body give a very good information that both + and - lines of ISD are not required to get the sound out put infact i need only one of these pins so now i am using + of ISD for telephone line and - goes to the speaker and other end of speaker to ground. its working for both spekar and telephone.

now i need to share the speaker between ISD and the uC speaker interface. I can use one relay for this purpose. relay can connect the speaker to ISD line if i want the message in ISD be heard on speaker. but for normal operation relay will connect the speaker to TIP125 transistor collector pin. The problem is 68O oham 1 W resistor connected between speaker and Ground. if ISD is connected to speaker---68Oham---Ground then there will be no sound from ISD. ISD will only work when SPeaker is directly connected to Ground. So i need such a arrangement that speaker connected direclty to ground and for this i need to arrange the 68Oham resistor in the uC spekaer interface. This way i can share speaker between uC and ISD chip using a relay. Rememeber uC Speaker interface is used to produce a beep like sounds to indicate a key has been pressed.


I am not good in analog business, only digital. so any suggestion how to adjust 68Oham resistor or suggest me any other circuit which can produce beep like sounds form spekaer and spekaer is connected direclty to gound.


thanks
Shahzad Aslam