Showing posts with label changeover. Show all posts
Showing posts with label changeover. Show all posts
Monday, December 16, 2013
Two Line Intercom Cum Telephone Line Changeover
The circuit presented here can be used for connecting two telephones in parallel and also as a 2-line intercom. Usually a single telephone is connected to a telephone line. If another telephone is required at some distance, a parallel line is taken for connecting the other telephone. In this simple parallel line operation, the main problem is loss of privacy besides interference from the other phone. This problem is obviated in the circuit presented here. Under normal condition, two telephones (telephone 1 and 2) can be used as intercom while telephone 3 is connected to the lines from exchange. In changeover mode, exchange line is disconnected from telephone 3 and gets connected to telephone 2.
2-Line Intercom-Cum-Telephone Line Changeover Circuit Diagram
For operation in intercom mode, one has to just lift the handset of phone 1 and then press switch S1. As a result, buzzer PZ2 sounds. Simultaneously, the side tone is heard in the speaker of handset of phone 1. The person at phone 2 could then lift the handset and start conversation. Similar procedure is to be followed for initiation of the conversation from phone 2 using switch S2. In this mode of operation, a 3-pole, 2-way slide-switch S3 is to be used as shown in the figure. In the changeover mode of operation, switch S3 is used to changeover the telephone line for use by telephone 2. The switch is normally in the intercom mode and telephone 3 is connected to the exchange line.
Before changing over the exchange line to telephone 2, the person at telephone 1 may inform the person at telephone 2 (in the intercom mode) that he is going to changeover the line for use by him (the person at telephone 2). As soon as changeover switch S3 is flipped to the other position, 12V supply is cut off and telephones 1 and 3 do not get any voltage or ring via the ring-tone-sensing unit. Once switch S3 is flipped over for use of exchange line by the person at telephone 2, and the same (switch S3) is not flipped back to normal position after a telephone call is over, the next telephone call via exchange lines will go to telephone 2 only and the ringtone-sensing circuit will still work. This enables the person at phone 3 to know that a call has gone through. If the handset of telephone 3 is lifted, it is found to be dead. To make telephone 3 again active, switch S3 should be changed over to its normal position.
Source: http://www.ecircuitslab.com/2011/11/two-line-intercom-cum-telephone-line.html
Wednesday, July 3, 2013
Auto Changeover from Generator to Mains Supply
Because of energy crisis Load shedding may be a common problem in several countries.. Sudden power fluctuations, surge and high voltage may spoil sophisticated household appliances like TV, VCR, VCP and music system. This circuit provides protection against these problems and automatically changes the power supply from Generator output to mains supply and also switches off the generator.
Circuit descriptions
This circuit is self explanatory. When lines supply voltage crosses the preset level, Zener diode ZD4 break down and thus transistor T2 conducts, T3 does not conduct, causing the relay to de-energise. Voltage surge at the time of power resumption is protected by the delay circuit around transistor T1.
All the portable petrol and kerosene generators have a connection from CDI. To stop the engine of the generator-set, this connection is to be grounded momentarily (through the switch). This lead is to be connected with the ground through the N/C point of the relay.
Auto Changeover from Generator to Mains Supply Circuit Diagram
Instead of the one transformer, two transformers are used in series to ensure better life of the unit. Value of capacitor C2 can be increased or decreased for the variation of delay time. A negative feedback resistance, R6 (15 K-ohm to 100 k-ohm) can be incorporated between transistor T3 and T4 to overcome the damage that could be caused by voltage fluctuations.
Parts List:
Resistors (all ¼-watt, ± 5% Carbon)
R1 = 10 Ω
R2 = 1 KΩ
R3 = 820 Ω
R4 = 57 KΩ
R5 = 47 Ω
R6 = (15 KΩ to 100 KΩ)
Capacitors
C1 = 100 µF/25V
C2 = 1000 µF/12V
C3 = 100 µF/18V
Semiconductors
T1 = BC147
T2, T3 = SL100
D1, D2 = 1N4001
D3 = 1N4007
ZD1 = 5.6V/400mW
ZD2 = 7.8V/400mW
Miscellaneous
X1, X2 = 230V AC primary to 12 V, 500mA secondary transformers
RL1 = 12V/450 Ω relay
Circuit descriptions
This circuit is self explanatory. When lines supply voltage crosses the preset level, Zener diode ZD4 break down and thus transistor T2 conducts, T3 does not conduct, causing the relay to de-energise. Voltage surge at the time of power resumption is protected by the delay circuit around transistor T1.
All the portable petrol and kerosene generators have a connection from CDI. To stop the engine of the generator-set, this connection is to be grounded momentarily (through the switch). This lead is to be connected with the ground through the N/C point of the relay.
Auto Changeover from Generator to Mains Supply Circuit Diagram
Instead of the one transformer, two transformers are used in series to ensure better life of the unit. Value of capacitor C2 can be increased or decreased for the variation of delay time. A negative feedback resistance, R6 (15 K-ohm to 100 k-ohm) can be incorporated between transistor T3 and T4 to overcome the damage that could be caused by voltage fluctuations.
Parts List:
Resistors (all ¼-watt, ± 5% Carbon)
R1 = 10 Ω
R2 = 1 KΩ
R3 = 820 Ω
R4 = 57 KΩ
R5 = 47 Ω
R6 = (15 KΩ to 100 KΩ)
Capacitors
C1 = 100 µF/25V
C2 = 1000 µF/12V
C3 = 100 µF/18V
Semiconductors
T1 = BC147
T2, T3 = SL100
D1, D2 = 1N4001
D3 = 1N4007
ZD1 = 5.6V/400mW
ZD2 = 7.8V/400mW
Miscellaneous
X1, X2 = 230V AC primary to 12 V, 500mA secondary transformers
RL1 = 12V/450 Ω relay
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