The “OOK modulation” or On Off Keying Modulation is very popular now days due to VLC or Visible Light Communication. OOK modulation is easy to use and easy to implement. As we can even implement this modulation using simple 555 timer IC. In this post we are going to explain How to implement OOK Modulation using 555 timer IC?.
ASK vs OOK:
OOK modulation is simplest form of ASK or Amplitude Shift Keying Modulation. Many people confuse these two modulations and try to differentiate between two of them.
These two modulations are not different but OOK is a type of ASK. In ASK we modulate the data in amplitude vise as we reduce amplitude in 0 and send full carrier wave when we need to send ‘1’. But in other hand In OOK modulation we only transmit carrier if we want to transmit ‘1’ and when we need to transmit 0 we just simply send ‘0’ and no carrier wave in that time.
The very famous research paper about OOK modulation explain this very well. You may see this paper for more detail.
OOK Modulator Circuit:
To modulate digital data using OOK modulation Technique we need to have a carrier wave and then we need to get dot product of carrier with data bit stream. Once we get these two waveform multiplied the output waveform will be On Off keying Modulated data, which we may transmit using our transmitter circuit.
To implement this technique all we need is to build Astable Multivibrator. We do this using 555 timer ic. we can also make Astable Multivibrator using simple transistors but this is not the topic of current tutorial. You may see few articles upon 555 timer implementations as Astable multivibrator in following links
- Astable Multivibrator using 555
- 555 Timer Astable Multivibrator Circuit
We apply our data wave on Reset pin of 555 timer IC which will simply oscillate when the data is ‘1’ and will not oscillate when the input data is ‘0’. Here is waveform output we get in proteus simulation