Harness your biopotential, or: How to measure a heartbeat in approximately twelve steps
AN INTRODUCTION
The heart in your chest beats every minute of your life. [1] Accompanying each new beat is an electrical dance whose waves ripple throughout your body. The same is true of every single human being you will ever come across. What you will do is measure those waves between two points in space and thereby detect the exact moment a heart’s muscles contract for a few minutes of someone’s life one fine day.
To do this, you will construct a system, an electrocardiogram comprising the following:
Specifically, you will
(1) power up a prototyping electronics board to create a system,
(2) build an amplifier system to amplify a signal,
(3) construct a filter to remove unwanted noise from the signal,
(4) detect a heartbeat from a willing participant, and in the process
(5) become a biomedical engineer.
MATERIALS
Review material inventory
Begin by reviewing the inventory of your kit. Ensure it contains the following materials:
- Twenty (20) jumper wires, ~5 cm each (4 red, 4 black, 4 green, 4 yellow, 4 blue)
- Three (3) long wires, unstripped, ~15 cm each (1 red, 1 black, 1 green)
- Three (3) resistors
- RG: 1.5 kΩ; Actual value: ________________ Ω
- R1: 330 kΩ; Actual value: ________________ Ω
- R2: 10 MΩ; Actual value: ________________ Ω
- Two (2) capacitors
- C1: 10 µF Actual value: ________________ F
- C2: 100 pF Actual value: ________________ F
- One (1) AD620 instrumentation amplifier (Figure 1. AD620)
- One (1) LM741 operational amplifier (Figure 2. LM741)
[Note: You will need to measure each of the passive components (i.e., the resistors and the capacitors) to determine their value. To do this, a volunteer will show you how to measure these values with a multimeter.]
[Note still further: Sometimes smaller valued capacitors can be difficult to measure precisely.]
Review workstation equipment
Please also check your workstation for the following equipment:
- A breadboard (Twin Industries TW-E41-1060, Figure 3. A breadboard with posts, rails, trench, and terminals)
- A power supply (Agilent E3630A, Figure 4. A power supply with (A) voltage adjustment, (B) port selection, and (C) output ports)
- An oscilloscope (Tektronix TDS 2012C, Figure 5. An oscilloscope with (A) position and vertical scaling, (B) input, and C) horizontal scaling)
- Three (3) 2m banana cables (one red, two black; with connectors, Figure 6. Banana cables (2m))
- Three (3) 1m banana cables (one red, two black, Figure 7. Banana cables (1m))
- One (1) BNC-to-splitter cable (Figure 8. BNC-to-splitter cable)
1. Except in those rare instances of individuals with artificial hearts or transplants, techniques being ever more perfected by biomedical engineers and their collaborators.