A restricted phone project

[kukaraca]

Hi all.

Let me first clarify what I want to do.

I wanna build a telephone which can only dial 6 numbers in its memory (accessed by the user via buttons) and is only handsfree operated.
The ring tone will be given from the loudspeaker. Call start/receive/end will be done by one separate button.
There will be a GLCD to guide or inform the user about the current process.

These are the basic points actually.

Now, what do I need? What points should I be careful about? I need your help and experience.

Let me list the components İ will need as far as I know and you tell me my mistakes or missing parts.

- MCU, GLCD, DTMF Encoder, Microphone, Loudspeaker, Relay(s), line transformer, battery, various elements(capacitors, resistors, diodes, transistors, regulators),
and of course the integration of all

By the way, please feel free to make suggestions like shortcuts. For example; I found two legacy ICs (MC33215A and MC34216A) which are exactly what I want but I am not sure they are compatible with the PSTN in my country, they can communicate with the MCU I choose... I am not even sure these are what I am looking for

I appreciate any help. Thanks in advance.

 

[kukaraca]

I have realized that "restricted" is not the correct word Anyway...

 

[Externet]

Obtain a speakerphone with at least six memory speed dialer.
Save those 6 numbers in memories.
Disable the numerical keypad by disconnecting it and use the memory dialing buttons.

As you say you want to build one; As soon as the unit above works as you intended, you can dismantle it to pieces and make an schematic of everything the way it was.
Now you have ALL the parts and the instructions to build one, put it back together. No wait for designing / searching / ordering parts

 

[kukaraca]

Thanks.

Since I told you only the basic features of what I want to build, your advice is pretty good.
I actually gave it a try but all the phones in the market are too compact, hard to interfere in for me to implement extra things.

This will be an original product. I should build it from scratch so that I can develop it.
For example: All calls will have a maximum duration, say 3 minutes.

 

[SUMIT_GAMBHIR]

dear, the restriction of Call duration can always be embedded in the software

 

[kukaraca]

I will do it that way. My intention was to clarify that a phone like Externet just proposed is not enough.