#Free schematics online how to
#Free schematics online manual

The circuit uses only two ICs and it can be implemented very easily. The circuit shown here is used to switch on a lamp when the tele- phone rings, if the ambient light is insufficient. The circuit can be suitably adopted for calling-line ШЇЩЉШіШЁЩ„ Also, different colour displays can be used for the first three or four digits to separate the exchange code/STD code, etc. To make the system compact, small, 7-segment displays can be used but with some extra cost. The present circuit can be built on a veroboard and housed in a suitable box. For doing this, connect the reset pin of IC2, say, for a 7-digit display, with S6 output at pin 5.

Though this circuit is capable of showing a maximum of ten digits, one can reduce the display digits as required. The power-supply switch can also be replaced then.

#Free schematics online manual

The system should be connected to the telephone lines via a DPDT switch (not shown) for manual switching, otherwise any circuit capable of sensing handsetвЂ™s off-hook condition and thereby switching relays, etc. For instance, contents of IC5A are displayed on display вЂDIS1,вЂ™ that of IC5B on вЂDIS2вЂ™ and so on. When a latch is enabled, its corresponding display is turned on and the content of that latch, after decoding by IC10, gets displayed in the corresponding display. IC3 also drives the displays by switching corresponding transistors. IC3 is clocked by an astable multivibrator IC4 (555). The output from a latch is available only when its disable pins (3 and 15) are brought low. This not only reduces size and cost but reduces power requirement too. There is only one 7-segment decoder/driver IC10 for all the ten displays. The similar input and output pins of all latches are connected together to form two separate input and output buses. Then, on clocking IC2, the same pin becomes low and the data present at the inputs of that latch at that instant gets stored and the next latch is cleared and kept ready. When an output pin of IC2 is high, the corresponding latch is cleared of previous data and kept ready for storing new data. The ten outputs of IC2 are sequentially connected to the store and clear inputs of all the latches, except the last one, where the clear input is tied to ground. The data valid output from pin 15 of IC1 is used to clock IC2. The storing of numbers in respective latches is done by IC2 (4017). This is accomplished by gates N13 through N15 (IC11) and N1 (IC12). Therefore the binary output of IC1 is passed through a logic-circuit which converts an input of вЂ10102вЂ™ into вЂ00002вЂ™ without affecting the inputs вЂ1вЂ™ through вЂ9вЂ™.

The binary output from IC1 for digit вЂ0вЂ™ as decoded by IC1 is 10102 (=1010), and this cannot be displayed by the seven-segment decoder, IC10.

The first number is stored in IC5A (1/2 of CD4508) while the second number is stored in IC5B and so on. This binary number is stored sequentially in 10 latches each time a number is dialled from the phone. The DTMF signal-generated by the phone on dialling a number-is decoded by DTMF decoder CM8870P1 (IC1), which converts the received DTMF signal into its equivalent BCD number that corresponds to the dialled number. This is particularly helpful for receiving any number over the phone lines. This circuit can also show the number dialled from the phone of the called party. The given circuit, when connected in parallel to a telephone, dis- plays the number dialled from the telephone set using the DTMF mode.

#Free schematics online how to

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