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Biomedical Instrumentation Lab Lab Experiments

Opto-isolation amplifier lab experiment


To measure pulse rate and to study the characteristics of opto isolation amplifier.

Apparatus Required:

  1. Transducer : 1 with 1.5 meter, EP pin
  2. Mains Cord : 1 Three pin with Socket
  3. Test Probe : 2 2mm set.
  4. Opto isolation Kit.
  5. DSO
  6. Connecting Cables

Installation Procedure:

1. Connect the instrument to the mains.


2. Connect the Transducer to system

Insert the transducer plug into the transducer socket.

mains cord

3. Use storage Oscilloscope.

  1. Now switch ON DSO.
  2. Put the DSO on storage mode,
  3. Mode switch at DC position, Probe on 'X1' position.
  4. Time / Div Knob on the 50mS Division. (Change the position as per signal)
  5. Voltage / Div Knob on the 5V. (Change the position as per signal)

4. Now connect the DSO to the instrument.

Connect DSO probe to instrument at Pulse output 2mm red socket & Black socket Ground.

5. Putting the sensor

Put the finger on transducer & wrapped with Velcro around the finger. The transducer should not be too tight. Make arrangement of transducer as we get proper pulse. If there is any moments not get the proper readings. There are reading ± 2 digits up & down. Adjust threshold/Gain control if Pulse is not proper.


6. See signal Pattern on DSO

If Pulse not properly, adjust threshold control knob.

7. Display shows the Heart Rate. Red LED is indication of Heart Pulse. This same to Optical Isolation amplifier. No movement, person must in rest position

8. Check the ground; if not proper make arrangement for that.id2

9. Now DSO Connect at isolation Output.

Green LED indication of Pulse output of Isolation amplifier. Red LED ON Green OFF & Pulse from Positive to Ground.

Block diagram:

optical isolation amplifier using heart pulse

Measurement of Pulse Rate

Plethysmography is a non-invasive method for studies of the heart rate. This pulse wave will result in a change in the volume of arterial blood with each pulse beat. This change in blood volume can be detected in peripheral parts of the body such as the fingertip or ear lobe using a technique called Photo plethysmography. The device that detects the signal is called a plethysmography.

Heart rate measurement indicates the soundness of the human cardiovascular system. The transducer consists of a Red LED that transmits an LDR through the fingertip of the subject, a part of which is reflected by the blood cells. The reflected signal is detected by a sensor. The changing blood volume with heartbeat results in a train of pulses at the output of the sensor, the magnitude is too small.


The Pulse to Pulse interval measures the period of heart beat is denoted by the following Formula

The Pulse to Pulse interval measures the period of heart beat is denoted by the following

T=Pulse to pulse Interval in Second. (P-P)

Where HR is the heart rate measured in beat-per-minute (BPM), interval measured in millisecond (ms). For example, if P-P is 800 ms, the heart rate is 75 BPM.

Tabular Column

Sr. No Subject Pulse time ms Calculated HR HR Display


Opto-isolators or Opto-couplers, are made up of a light emitting device, and a light sensitive device, all wrapped up in one package, but with no electrical connection between the two, just a beam of light. The light emitter is nearly always an LED. The light sensitive device may be a photodiode, phototransistor, or more esoteric devices such as thyristors, TRIACs etc.

The opto-coupler is a component that contains the two elements required for an opto-isolator: Light emitter: The light emitter is on the input side and takes the incoming signal and converts it into a light signal. Typically the light emitter is a light emitting diode.

Light detector: The light detector within the opto-coupler or opto-isolator detects the light from the emitter and converts it back into an electrical signal. The light detector can be any one of a number of different types of device from a photodiode to a phototransistor, photodarlington, etc.

Opto-coupler symbol:


The symbol shows the LED, which is normally used as the light emitter. The opto-coupler symbol also shows the receiver, often a phototransistor or photodarlington, although other devices including light sensitive diacs, etc may also be used. The relevant device type is shown within the optocoupler circuit symbol.

Application of MCT2E:It is a combination of 1 LED and a transistor. Pin 6 of transistor is not generally used and when light falls on the base-emitter junction then it switches and pin5 goes to zero.

MCT2E Opto-Coupler - Circuit


When logic zero is given as input then the light doesn’t fall on transistor so it doesn’t conduct which gives logic one as output. When logic 1 is given as input then light falls on transistor so that it conducts, that makes transistor switched ON and it forms short circuit this makes the output is logic zero as collector of transistor is connected to ground.


The Characteristics of opto-isolation amplifier was studied and Pulse rate was measured.