Telephone Light Ringer
#telephone
#light ringer
#LDR
#automatic switching
#battery powered
#programmable timer
#home automation
#bedroom
#energy saving
Description: The circuit shown here is used to switch on a lamp when the telephone rings, if the ambient light is insufficient. The circuit uses only two ICs and it can be implemented very easily. A light dependent resistance (LDR), with about 5 kilo-ohms resistance in the ambient light and greater than 100 kilo-ohms in darkness, is at the heart of the circuit. The circuit is fully isolated from the phone lines and it draws current only when the phone rings. The circuit provides automatic switching on of a lamp during darkness when the phone is kept in a place such as the bedroom. The lamp can be battery powered to provide light during power failure or load shedding. This avoids delay in attending to a call. The light switches off automatically after a programmable time period and it needs no attention at all. If required, the lamp lighting period can be extended by simply pressing a pushbutton switch (S1).
The circuit operates as a ring detector and lamp controller, utilizing two integrated circuits (ICs) for functionality. The first IC is an opto-coupler that isolates the circuit from the telephone lines. When the telephone is on-hook, approximately 48V DC is present across the TIP and RING terminals, keeping the diode in the opto-coupler off, thereby drawing minimal current. Upon an incoming call, an AC voltage of about 70-80V is generated across the telephone lines, activating the diode within the opto-coupler (IC2). This, in turn, energizes the internal transistor, resulting in a voltage drop at the collector that triggers the first 74LS123(A) monostable flip-flop.
The second opto-coupler (IC1) monitors ambient light conditions via a light-dependent resistor (LDR). In bright conditions, the LDR exhibits low resistance (approximately 5 kilo-ohms), keeping the internal transistor of the opto-coupler in an on state. Conversely, in darkness, the LDR's resistance increases significantly, switching the transistor off and causing the collector voltage to rise to 5V. The 74LS123(A) monostable flip-flop generates a programmable pulse-width signal when triggered by the ringing phone, provided that the ambient light condition indicates darkness.
The output from the first monostable flip-flop serves as a trigger for the second 74LS123(B) monostable flip-flop, which controls a relay that powers the lamp. The duration for which the lamp remains on is determined by the pulse-width set within the second monostable circuit. Additionally, the lamp's on period can be extended by pressing the pushbutton switch (S1). If the call is not attended to, the lamp automatically turns off after the preset time period determined by the second flip-flop's configuration.
Adjustments can be made to fine-tune the light sensitivity of the LDR by varying the resistance of R2 connected to the collector of the light monitor circuit's transistor. Similarly, the duration for which the lamp is activated can be modified by changing the capacitance of capacitor C3 in the second 74LS123(B) monostable circuit. This design allows for flexibility in operation and ensures reliable performance in various lighting conditions.The circuit shown here is used to switch on a lamp when the tele- phone rings, if the ambient light is insufficient. The circuit uses only two ICs and it can be implemented very easily. A light dependent resistance (LDR), with about 5 kilo-ohms resistance in the ambient light and greather than 100 kilo-ohms in darkness, is at the heart of the circuit.
The circuit is fully isolated from the phone lines and it draws current only when the phone rings. The circuit provides automatic switching on of a lamp during darkness when the phone is kept in a place such as the bedroom. The lamp can be battery powered to provide light during power failure or load shedding. This avoids delay in attending to a call. The light switches off automatically after a programmable time period and it needs no attention at all.
If required, the lamp lighting period can be extended by simply pressing a pushbutton switch (S1). The first part of the circuit functions as a ring detector. When telephone is on-hook, around 48V DC is present across the TIP and RING terminals. The diode in the opto-coupler is off during this condition and it draws practically no current from he telephone lines. The opto-coupler also isolates the circuit from the telephone lines. Transistor in the opto-coupler is normally off and a voltage of +5V is present at the ring indicator line.
When telephone rings, an AC voltage of around 70-80V AC, which is present across the telephone lines, is used to turn on the diode inside the opto-coupler (IC2) which in turn switches on transistor inside the opto-coupler. The voltage at its collector passes through 0-volt level during ringing to trigger IC3 74LS123(A) monostable flip-flop.
The other opto-coupler (IC1) is used to detect the ambient light condition. When there is sufficient light, LDR has a low resistance of about 5 kilo-ohms and the transistor inside the opto-coupler is in on state. When there is insufficient light available, the resistance of LDR increases to a few mega-ohms and the transistor switches to off state.
Thus the DC voltage present at the collector of transistor inside the opto-coupler is normally 0V and it jumps to 5V when there is no light or insufficient light. The 74LS123 retriggerable monostable multivibrator is used to generate a programmable pulse-width. The first monostable 74LS123(A) generates a pulse from the trigger input available during ringing, provided its pin 2 input (marked B) is logic high (i.e.
during darkness). It remains high for the programmed duration and switches back to 0V at the end of the pulse period. This high-to-low transition (trailing edge) is used to trigger the second monostable flip-flop 74LS123(B) in the same package. Output of the second monostable is used to control a relay. The lamp being controlled via the N/O contacts of the relay gets switched on. The on period can be extended by simply pressing pushbutton switch S1. If nobody attends the phone, the light turns off automatically after the specific time period equal to the pulse-width of the second flip-flop.
The light sensitivity of LDR can be changed by changing resistance R2 connected at collector of the transistor in light monitor circuit. Similarly, switch-on period of the lamp can be controlled by changing capacitor C3s value in the second 74123(B) monostable circuit.
The circuit operates as a ring detector and lamp controller, utilizing two integrated circuits (ICs) for functionality. The first IC is an opto-coupler that isolates the circuit from the telephone lines. When the telephone is on-hook, approximately 48V DC is present across the TIP and RING terminals, keeping the diode in the opto-coupler off, thereby drawing minimal current. Upon an incoming call, an AC voltage of about 70-80V is generated across the telephone lines, activating the diode within the opto-coupler (IC2). This, in turn, energizes the internal transistor, resulting in a voltage drop at the collector that triggers the first 74LS123(A) monostable flip-flop.
The second opto-coupler (IC1) monitors ambient light conditions via a light-dependent resistor (LDR). In bright conditions, the LDR exhibits low resistance (approximately 5 kilo-ohms), keeping the internal transistor of the opto-coupler in an on state. Conversely, in darkness, the LDR's resistance increases significantly, switching the transistor off and causing the collector voltage to rise to 5V. The 74LS123(A) monostable flip-flop generates a programmable pulse-width signal when triggered by the ringing phone, provided that the ambient light condition indicates darkness.
The output from the first monostable flip-flop serves as a trigger for the second 74LS123(B) monostable flip-flop, which controls a relay that powers the lamp. The duration for which the lamp remains on is determined by the pulse-width set within the second monostable circuit. Additionally, the lamp's on period can be extended by pressing the pushbutton switch (S1). If the call is not attended to, the lamp automatically turns off after the preset time period determined by the second flip-flop's configuration.
Adjustments can be made to fine-tune the light sensitivity of the LDR by varying the resistance of R2 connected to the collector of the light monitor circuit's transistor. Similarly, the duration for which the lamp is activated can be modified by changing the capacitance of capacitor C3 in the second 74LS123(B) monostable circuit. This design allows for flexibility in operation and ensures reliable performance in various lighting conditions.The circuit shown here is used to switch on a lamp when the tele- phone rings, if the ambient light is insufficient. The circuit uses only two ICs and it can be implemented very easily. A light dependent resistance (LDR), with about 5 kilo-ohms resistance in the ambient light and greather than 100 kilo-ohms in darkness, is at the heart of the circuit.
The circuit is fully isolated from the phone lines and it draws current only when the phone rings. The circuit provides automatic switching on of a lamp during darkness when the phone is kept in a place such as the bedroom. The lamp can be battery powered to provide light during power failure or load shedding. This avoids delay in attending to a call. The light switches off automatically after a programmable time period and it needs no attention at all.
If required, the lamp lighting period can be extended by simply pressing a pushbutton switch (S1). The first part of the circuit functions as a ring detector. When telephone is on-hook, around 48V DC is present across the TIP and RING terminals. The diode in the opto-coupler is off during this condition and it draws practically no current from he telephone lines. The opto-coupler also isolates the circuit from the telephone lines. Transistor in the opto-coupler is normally off and a voltage of +5V is present at the ring indicator line.
When telephone rings, an AC voltage of around 70-80V AC, which is present across the telephone lines, is used to turn on the diode inside the opto-coupler (IC2) which in turn switches on transistor inside the opto-coupler. The voltage at its collector passes through 0-volt level during ringing to trigger IC3 74LS123(A) monostable flip-flop.
The other opto-coupler (IC1) is used to detect the ambient light condition. When there is sufficient light, LDR has a low resistance of about 5 kilo-ohms and the transistor inside the opto-coupler is in on state. When there is insufficient light available, the resistance of LDR increases to a few mega-ohms and the transistor switches to off state.
Thus the DC voltage present at the collector of transistor inside the opto-coupler is normally 0V and it jumps to 5V when there is no light or insufficient light. The 74LS123 retriggerable monostable multivibrator is used to generate a programmable pulse-width. The first monostable 74LS123(A) generates a pulse from the trigger input available during ringing, provided its pin 2 input (marked B) is logic high (i.e.
during darkness). It remains high for the programmed duration and switches back to 0V at the end of the pulse period. This high-to-low transition (trailing edge) is used to trigger the second monostable flip-flop 74LS123(B) in the same package. Output of the second monostable is used to control a relay. The lamp being controlled via the N/O contacts of the relay gets switched on. The on period can be extended by simply pressing pushbutton switch S1. If nobody attends the phone, the light turns off automatically after the specific time period equal to the pulse-width of the second flip-flop.
The light sensitivity of LDR can be changed by changing resistance R2 connected at collector of the transistor in light monitor circuit. Similarly, switch-on period of the lamp can be controlled by changing capacitor C3s value in the second 74123(B) monostable circuit.
Soft Musical Telephone Ringers
The standard telephone bell can be quite bothersome, especially at night when disturbances are unwanted. The circuit presented here transforms the loud ringing bell into a gentle and pleasant musical tone. The incoming ringing signal is detected by transistor T1...
Automatic Street Light Controller Circuit
This circuit is an automatic street light controller. The sensor used to detect changes in light is an LDR (Light Dependent Resistor). The working principle of the LDR is that when exposed to light, its resistance value decreases, while in...
ring generator circuit
This design aims to restore the classic style of telephones that utilized a pair of gongs to signal an incoming call, evoking a sense of nostalgia with the familiar sound of ringing bells. Presented here is a "Telephone Ring Generator"...
Telephone-amplifier
Audio from the telephone is inductively coupled to the base of Q1, which functions as a preamplifier. This preamplifier provides a gain of approximately 75 dB, boosting the input signal from around 4 mV to about 300 mV peak-to-peak. If...
Telephone Ring Generator Using Small Power Transformer
The interval between rings can be adjusted by changing the value of the 1 Meg resistor. A 70 volt, 30 Hz ringing voltage is generated from the 120 volt side of a small 12.6 VAC power transformer (Radio Shack 273-1365)....
Very Simple Telephone Intercom Circuit Circuit
Two telephones can be used as an intercom by utilizing this circuit. Older style rotary phones that are non-electronic may be the most suitable for this application. Additionally, handsets alone can be powered in this manner.
This intercom circuit allows for...
Battery powered buffer amplifier
This circuit exhibits negligible loading and disconnects the cell in response to low supply voltage or an overload on the output. Additionally, the indicator diode turns off when the disconnect circuitry is activated.
The circuit design incorporates a voltage monitoring mechanism...
home automation Installation
First and foremost, if one is not skilled with tools and electrical systems, it is advisable to hire a qualified electrician rather than attempting to undertake this task independently. The electrician should review this page for specific cautions and advice....
Automatic telephone call recording circuit
The DC voltage present on the telephone line typically ranges from 45 to 50V when on-hook and drops to approximately 6V when off-hook. This condition activates a step-down circuit relay, which in turn controls a tape recorder. Audio input is...