With this circuit mounted in or near every phone in the house, it will allow users to know if the phone is being used and not to pick up the phone. When a phone is taken off hook, the voltage across the tip and ring terminals drops to 10 volts or less. This will cause the FET (2N4360) to turn on and also turn on the transistor (2N2222). When the transistor turns on it will allow current to flow through the LED and make it light. A blinking LED could be used to make the effect better. Copyright 1999 [url=http://home.maine.rr.com/randylinscott/index.html]Randy...

This circuit will allow you to place a phone call on hold and if you wish to have them listen to music while they are on hold. The circuit operates as follows: The RED wire from the phone jack is typically positive and the GREEN wire is negative or ground. When you want to place a call on hold, close S1 and hang up the handset. The resistor R1 simulates another phone off hook and allows enough current to pass through to prevent the phone company from disconnecting the call. The resistor R2 and LED provide a visual indication that you have someone on hold ( this is optional ) The capacitor C1...

This circuit will allow you to connect any tape recorder that has a mic and remote input to a phone line and automatically record both sides of a conversation when ever the phone is in use. You will need to take a couple of voltage readings before connecting the circuit. First determine the polarity of your phone line and connect it to the circuit as shown and then determine the polarity of the remote input and connect it to the circuit. Circuit operation is as follows. When the phone is on hook the voltage across the phone line is about 48volts dc. When the phone is off hook the voltage...

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...

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...

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=http://ourworld.compuserve.com/homepages/Bill_Bowden/]Bill Bowden[/url]...

The telephone ring generator shown above generates the needed high voltage from a simple switching mode power supply (SMPS) which employs a CMOS Schmitt Trigger square wave oscillator, 10 mH inductor, high voltage switching transistor (TIP47 or other high voltage, 1 amp transistor) and a driver transistor (2N3053). The inductor should have a low DC resistance of 1.5 ohms or less. The switching supply must have a load connected to prevent the voltage from rising too high, so a 22K resistor is used across the output which limits the voltage to about 120 DC with the phone ringer disconnected and...

See image above Copyright 2006: Bill Bowden [url]http://ourworld.compuserve.com/homepages/Bill_Bowden/[/url]...

See image above Copyright 2006: Bill Bowden [url]http://ourworld.compuserve.com/homepages/Bill_Bowden/[/url]...

Audio from a telephone line can be obtained using a transformer and capacitor to isolate the line from external equipment. A non-polarized capacitor is placed in series with the transformer line connection to prevent DC current from flowing in the transformer winding which may prevent the line from returning to the on-hook state. The capacitor should have a voltage rating above the peak ring voltage of 90 volts plus the on-hook voltage of 48 volts, or 138 volts total. This was measured locally and may vary with location, a 400 volt or more rating is recommended. Audio level from the...

From: mwandel@bnr.ca (Markus Wandel) I have recently thought about this and come up with a kludgy but workable scheme. Talking over the phones is easy. You put DC current through the phone and it transmits and receives audio. So two phones and a current source (about 25mA) all in series will give you a talking circuit. A suitable current source can be as simple as a 9V battery and a series resistor whose value is adjusted (with both phones offhook) till about 25mA flows. You can then bypass the battery and the resistor with a capacitor to couple the audio straight across and get a loud...

This is very useful in a situation were there is lots of noise and it is impossable to hear the phone, such as a workshop. Here is such a device. The ring detect part of this circuit came from [url]http://www.hut.fi/Misc/Electronics/circuits/telephone_ringer.html[/url]. Notes: 1. You may need to use a lower voltage zener for D1 and D2. 2. You can use a regular relay instead of a solid state relay, but the arcing accross the contacts may destroy it pretty quickly. 3. Be very sure that you have not accidentally connected 120V to the phone line when building and installing this...