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PICList Thread
'phone password'
1999\02\02@183035 by Hanafi Tanudjaja

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A friend of mine interested to add a password for his privat telphone.
So that only certain person who knows the password can call him.
I don't have the idea of the block diagram of this unit .
Any suggestion ?

TIA
Hanafi T

1999\02\02@185604 by Regulus Berdin

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Hanafi Tanudjaja wrote:
>
> A friend of mine interested to add a password for his privat telphone.
> So that only certain person who knows the password can call him.
> I don't have the idea of the block diagram of this unit .
> Any suggestion ?

Hi,

This is simply done by having a ring detector and having a PIC pick up
the phone and accepts dtmf thru a dtmf decoder.  Process it and sends a
ring signal to the phone until it is picked up or timeout.

A nice thing to do also is to have a speaker independent voice
recognition.  This way, a 'real' password is accepted.

regards,
Reggie

1999\02\02@201532 by Greg Cormier

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>This is simply done by having a ring detector and having a PIC pick up
>the phone and accepts dtmf thru a dtmf decoder.  Process it and sends a
>ring signal to the phone until it is picked up or timeout.


Yup. This can be done nicely with a 50 volt Zener I believe, and hook that
up to an optoisolator. It will pick up the line before any phone in the
house gets a chance to ring... I'm not sure about the 50 volts... Just make
it about 10-15 V higher than the normal not-in-use voltage.

-greg


-----------------------
Greg Cormier
Kathmandu, Nepal
Local time : GMT + 5h30m
spam_OUTgcormierTakeThisOuTspamwlink.com.np
ICQ # : 565465

1999\02\02@222448 by dave vanhorn

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>Yup. This can be done nicely with a 50 volt Zener I believe, and hook that
>up to an optoisolator. It will pick up the line before any phone in the
>house gets a chance to ring... I'm not sure about the 50 volts... Just make
>it about 10-15 V higher than the normal not-in-use voltage.


On a US line, 90V rms ring @20 hz, you want something more like 70V.
Or, rectify the line to DC, and look for >120V.

1999\02\03@101548 by Tom Handley
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  Hanafi, I also agree with Reggie's approach. TI makes a nice little Ring
Detector; TMC1520A. This comes in an 8-pin DIP and connects directly to the
phone line (USA specs). It requires two external capacitors and resistors.
Features include:

     Line powered
     5V regulated output for optoisolators
     150V Diode bridge
     1M Input impedance in standby
     Ringer equivalence < 1
     Lightning and Transient protection
     TTL/CMOS output

  I once designed a BBS monitor that detected incomming calls on several
lines and reset the host computer if the modem or software did not respond
within `n' number of rings. In addition to the 1520, I used a PIC16C84 and a
4N33 optoisolator. You can easily add a DTMF decoder to the '84.

  This is an old chip and I'm not sure if TI is still sourcing it but JDR
Microdevices has them for $1.29. The P/N is; TCM1520. JDR is at:

     http://www.jdr.com

  - Tom

At 07:59 AM 2/3/99 +0800, Hanafi and Reggie wrote:
{Quote hidden}

1999\02\03@193136 by WIL REEDER

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Hanafi
In addition to this check out Terry Weeder's site http://www.weedtech.com/
to see if one of his kits would do the job. Most of his stuff is PIC based
and he is easy to do business with. Just a thought.


Wil Reeder
.....teachtechKILLspamspam@spam@bc.sympatico.ca
Vancouver,Canada 0x33
solar,wind,tide, TEG  renewable energy
----------
| From: Tom Handley <thandleyspamKILLspamTELEPORT.COM>
| To: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU
| Subject: Re: phone password
| Date: Wednesday, February 03, 1999 6:53 AM
|
|    Hanafi, I also agree with Reggie's approach. TI makes a nice little
Ring
| Detector; TMC1520A. This comes in an 8-pin DIP and connects directly to
the
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