Phone in use indicator by LED
This circuit is useful to show chen your line is busy. I used for this a pair of smt transistor, the leds on when the voltage drop down to 40 v....
Doppler Compensation
The relative motion between a satellite and an observer causes a frequency shift known as the Doppler effect. Doppler is well-understood and can be corrected au...
Doppler Compensation
The relative motion between a satellite and an observer causes a frequency shift known as the Doppler effect. Doppler is well-understood and can be corrected au...
The Link Telephone Intercom
It uses old pulse dial handsets and replaces the AC bell set with a 9 volt DC buzzer. The whole circuit runs from a 12 volt regulated DC supply and is suitable ...
The Link Telephone Intercom
It uses old pulse dial handsets and replaces the AC bell set with a 9 volt DC buzzer. The whole circuit runs from a 12 volt regulated DC supply and is suitable ...
Isolated Telephone Interface
There`s not much to this circuit. The two RJ-11 jacks are set up to feed the telephone circuit through from the wall to the phone. The active signal for a singl...
Isolated Telephone Interface
There`s not much to this circuit. The two RJ-11 jacks are set up to feed the telephone circuit through from the wall to the phone. The active signal for a singl...
DTMF Tone Decoder
This project displays telephone numbers decoded from tones. A microphone picks up the tones, a preamplifier boosts the signals, an SSI-202 DTMF chip decodes the...
DTMF Tone Decoder
This project displays telephone numbers decoded from tones. A microphone picks up the tones, a preamplifier boosts the signals, an SSI-202 DTMF chip decodes the...
Telephone In Use Indicator Circuit
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...
Telephone In Use Indicator Circuit
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...
Telephone Record Control Circuit
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 w...
Telephone Record Control Circuit
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 w...
Bi-Directional Telephone Line
This self-build project can simulate a telephone call / connection between any two local telephone devices. This for a fraction of the outlay of some commercial...
Bi-Directional Telephone Line
This self-build project can simulate a telephone call / connection between any two local telephone devices. This for a fraction of the outlay of some commercial...
Conversation Recorder
This circuit enables automatic switching-on of the tape recorder when the handset is lifted. The tape recorder gets switched off when the handset is replaced. T...
Conversation Recorder
This circuit enables automatic switching-on of the tape recorder when the handset is lifted. The tape recorder gets switched off when the handset is replaced. T...
Cellular Phone calling Detector
This circuit was designed to detect when a call is incoming in a cellular phone (even when the calling tone of the device is switched-off) by means of a flashin...
Cellular Phone calling Detector
This circuit was designed to detect when a call is incoming in a cellular phone (even when the calling tone of the device is switched-off) by means of a flashin...
Telephone Ring Generator Using Switching Supply
The telephone ring generator shown below generates the needed high voltage from a simple switching mode power supply (SMPS) which employs a CMOS Schmitt Trigger...