This post is part of the series IC 555 Tested Mini Projects
Other posts in this series:
The IC555 frequency shift keying mini project is very simple to construct and can be made within an hour. The complete working and PCB layout of the circuit is also given below.
The telephone network is the prime medium, on global level, used for intercommunication on World Wide Web level i.e. to share the digital data from one computer to another. Generally, this medium is used with a modem to transfer the digital data from one computer to another. There are different types of modems used for data transfer over the internet through telephone lines and number of other mediums.
The most familiar example is a voice-band modem that turns the digital 1’s and 0’s of a computer into sounds that can be transmitted over the telephone lines of Plain Old Telephone Systems (POTS), and once received on the other side, converts those 1’s and 0’s back into a form used by a USB or Ethernet or other network connection.
However, modern telephone lines can carry digital signals like DSL (Digital Subscriber Line).The only time during which the telephone lines cannot carry digital signals is, if there is no receiving station of digital signals. Or the wires are too old and cannot carry higher frequency signals required for digital data.
In digital communication network, basically, the binary signal is transmitted by shifting the carrier signal between two preset frequencies. Such transmission technique is called as FSK. In the following diagram the basic circuit of frequency shift keying is shown.
The two preset frequencies used in transmission are 1070Hz and 1270Hz. When digital input is equal to logic-0, transistor T1 is ON, and R1 & R3 are parallel. So output frequency f0 is given by –
When digital input is HIGH i.e. logic-1, transistor T1 is OFF and R3 is cut-off from R1. So output frequency (f1) is given by –
Simulated circuit of FSK
Following two circuit diagrams show the simulated circuits of FSK using IC555. We have simulated its working in Circuit Wizard and checked the output frequency graph for the standard values of R1 and R2 used in a simple circuit of AMV using IC 555.
We have noticed that the value R1 can be kept constant but the value of R2 requires to be changed in two different values i.e. for 1270Hz, the value of R2 = 56.3k and for 1070Hz its value should be R2 = 66.9k.
I have calculated these values using online IC555 calculator.