Telephone
Telephone ringtone generator circuit
This is a simple home telephone ringtone generator circuit which is built with applying only several electronic components / parts. It generates simulated telephone ringtone and requires only DC supply with 4.5V DC to 12V DC voltage.
One may possibly use this circuit in ordinary intercom or phone-type intercom. The sound is pretty loud when this circuit is operated on +12V DC power supply. Even so, the volume of ring sound can be adjusted. More >
dual line phone
This simple circuit of a duophone allows you to access two telephone lines through one telephone set. Each telephone conversation will remain entirely separate unless you choose to combine the two lines through a conference switch. More >
Telephone Line In-Use Indicator
This circuit gives a visual indication of whether a telephone line is in use or not, helping two or more people sharing the line to avoid interrupting each other’s calls. More >
Call Bell with welcome Indication
Here is a simple call bell circuit that displays a welcome message when somebody presses the call bell switch momentarily. The alphanumeric display can be fitted near the call bell switch. More >
TELEPHONE-OPERATED CALLING SYSTEM (DTMF)
This telephone-operated calling circuit is very helpful for doctors in calling the patients, in banks and in various other situations where persons have to be called or signalled. When you need to call a person amongst many standing outside your cabin, just lift the telephone handset off the cradle and press the respective number. The number of the person called will be displayed and a bell will sound to inform the person that it is his turn. More >
Full-duplex Intercom
This design allows to operate two intercom stations leaving the operator free of using his/her hands in some other occupation, thus avoiding the usual “push-to-talk” operation mode.
No complex changeover switching is required: the two units are connected together by means of a thin screened cable. More >
Teleremote Control
Here is a teleremote circui t which enable switching ‘on’ and ‘off’ of appliances through telephone lines. It can be used to switch appliances from any distance, overcoming the limited range of infrared and radio remote controls. More >
Telephone Hold Project for 2 phones in parallel
This Hold Phone Circuit will enable you to hang up one phone without losing the connection and move to another room or hall and pick up a different phone which is connected in parallel and continue your conversation. This feature is useful especially when you are staying in a house with different levels and having 2 telephones connected in parallel. More >
Multipurpose Circuit for telephone
This add-on device for telephones can be connected in parallel to the telephone instrument. The circuit provides audio-visual indication of on-hook, off-hook, and ringing modes. It can also be used to connect the telephone to a CID (caller identification device) through a relay and also to indicate tapping or misuse of telephone lines by sounding a buzzer. More >
FM Telephone Bug
Here is a simple transmitter that when connected to a phone line, will transmit anything on that line (execpt the dial tone) to any FM radio. The frequency can be tuned from 88 to about 94Mhz and the range is about 200 feet. It is extremely easy to build and is therefore a good, useful beginner project. More >