Post by thread:phone password

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

>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_OUTgcormierTakeThisOuTwlink.com.np ICQ # : 565465

>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.

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}>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

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 .....teachtechKILLspam@spam@bc.sympatico.ca Vancouver,Canada 0x33 solar,wind,tide, TEG renewable energy ---------- | From: Tom Handley <thandleyKILLspamTELEPORT.COM> | To: .....PICLISTKILLspam.....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 snip