Category Archives: Phone

Phone Screener with Voice

This unit is an upgrade of the previous phone call interceptor. Instead of using an answering machine to provide the outgoing message and recording functions, it uses the ISD4004 (from Windbond Electronics). The ISD4004 records up to 8 minutes of audio. I use the first several seconds for outgoing message prompts. The remaining time is used to record up to 30 messages, depending on message length.

Here is what this unit does…

When a call comes in it prompts the caller to enter the access code or to hit ‘0’ to leave a message. If the proper code is entered, the device ‘rings’ an external speaker and waits for a phone to be picked up. If the phone is not picked up after several rings, it says ‘good bye’ and hangs up the line.

The caller can hit ‘0’ at any time to leave a message. The message time is limited to 40 seconds.

Any of several phone extentions plugged into this device can be used to retrieve messages. The messages are played out thru any phone. They can also be accessed remotely by calling in and entering the ‘secret’ access code.

For now, I am just providing the [url=http://www.circuitdb.com/download.php?fileID=187]source file[/url] and the [url=http://www.circuitdb.com/download.php?fileID=186]schematic[/url]. for this project. Later, I hope to elaborate on the details of the design.

Copyright 2006 [url=http://mondo-technology.com/]Luhan Monat[/url]

Phone Intercepter 1

This device connects between the phone line, an answering machine, and your phones. When a phone call comes in, the answering machine picks up the call and informs the caller to enter the access code to ring the phone or to wait for the beep and leave a message. If the correct code is entered, the answering machine is immediately disconnected while the device generates phone ringing tones on an external speaker. Picking up any phone causes the device to return to its initial state.

The design of this device is greatly simplified by haveing the answering machine ‘do the talking’ and using a speaker as a ringer rather than actually generating a ring signal (90 volts) to actually ring the phones. The list of functions left to the device itself are as follows…..[list:a95152e297]1. Decode the DTMF frequencies from the phone line.
2. Detect the answering machine picking up the line.
3. Detect the local phone being picked up or hung up.
4. Detect the calling party haning up.
5. Generate a ring signal for the speaker.
6. Check to see if my bedroom door is closed.[/list:u:a95152e297]

The PIC16F870 chosen for this project has seval analog channels. One of these is used to capture the DTMF tones and decode the digits. The actual phone connections are made using a ‘hacked’ 5 line expandor from Radio Shack. Inside the casing, seperate connections were made to each of the connectors and run out thru the back of the case.

Since I live in a rather large house (with 5 other people at this time), I used a PA horn for the ringer/speaker. As a compromise to local sanity, the level of the ringer is reduced when I am sleeping or not at home. The ‘door sense’ input detects the ‘state’ of my bedroom door since that is where the speaker is located.

This is one of the most useful devices I have made lately. As usual, you can check out both the [url=http://www.circuitdb.com/download.php?fileID=185]source file[/url] and the [url=http://www.circuitdb.com/download.php?fileID=184]schematic[/url].

Copyright 2006 [url=http://mondo-technology.com/]Luhan Monat[/url]

Telephone Ring Generator Using Small Power Transformer

This ring generator will ring a telephone once every 10 seconds. The interval between rings can be lengthened or shortened by varying the value of the 1 Meg resistor. The 70 volt/ 30 Hz ring voltage is produced from the 120 volt side of a small 12.6 VAC power transformer (Radio Shack 273-1365). Both capacitors connected across the transformer windings are non-polarized / 100 volts. Circuit draws about 300mA from the 12 volt DC power supply during the ringing interval.

Copyright 2006 [url=www.bowdenshobbycircuits.info]Bill Bowden[/url]