Bio Signal Amplification

You would want to move robot controlled by your eyes , or probably make a bio signal controlled robot , you need to actually amplify Bio-signals.

Here i talk about a simple construction to amplify and filter bio-signals . In this particular project a robot is controlled with signals based on eye movement. To be more precise when the eye moves left the bot moves left. Similarly right straight and stop.

The various stages in this project is to acquire the bio signals properly. When the eye moves there is produced a micro-volt variations in the electrodes in that region around the eyes this they pick up those signals.

Prominent disturbances of bio-signal are from external sources of nice thus it needs Low pass filtering . After filtering it will need a section to amplify at the last stage and avoid the threshold noise that is produces.

All the above said is achieve in the following circuit diagram and the three sages are marked.

  1. Acquiring Bio-Signals
  2. Filtering external noise
  3. Signal Amplification

Stage (1) collects the Bio-signal and amplifies in the first stage with a AD622 instrumentation amplifier. This give a huge voltage amplification (i’ve heard its given out as samples… do check) . Once the amplified signal is obtained you’l have to low pass filter it.

These bio signals have a very low frequency around 8Hz or so and hence a good low pass filter would remove all the noise. The op-amp shown in the second and third stages are either a 741 or LM324 .

The last and output stage has a normal amplifier with a op-amp. The third stage also helps us set the threshold voltage so that only the bio signal is amplified. The ‘POT’ in the third stage is set accordingly such that the total output of this circuit is ‘0’ at no signal input.

This the output will be a voltage > O for a signal from the electrode or ‘NO VOLTAGE’ .

In case you’l want to analyse these signals in digital logic , i.e “is there a bio signal or not?” then use the IC 7414 as in out IR sensor circuit .

This is from a working project *

Author: Madan Thangavelu

Software Engineer

3 thoughts on “Bio Signal Amplification”

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