to 5V DC for the micro, and detect when the phone is ringing so the micro can alert the user in some way. So currently I need a way to step-down the line voltage which can vary. The BT line specs are linked to at the bottom for full details if anyone is interested. ![]() so detecting that is not much of an issue. The receiver for the handset has a switch to detect pick up. ![]() The 'Call Arrival Indication' (Ringing) will be between 100V and 40V AC rms. The BT spec's say the potential between the 2 telephone line terminals will not exceed 70V when off-line. So when the phone rings or the handset is picked up the power is turned on. ![]() I don't want the telephone expending too much power for no-reason since it will be idle most of the time. So I'm thinking some type of switch-mode power supply. If the electronics are placed inside the the case and they get quite hot the old Bakelite case might be at risk. coming up with a design that will fit the requirements. The part which I have limited experience with is the power supply side. So I'm thinking the micro is best to keep the component count low. I probably could find a DTMF generator but then I'd need to use say some 7400 series IC's to decode the rotary encoder. ![]() So I was thinking of small board running a ATtiny todo the detection of the pulses from the rotary encoder and convert those to DTMF. There is a little room in the case for some small electronics without removing the old components. I want to make it work with the newer telephone system. Hi Everyone, So one of my current projects to to make a converter for an old BT #332 phone.
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