⟵ 3. CONSTRUCT A FILTER
In this portion of the activity, you will actually be measuring actual heartbeats from an actual person. To observe the heart’s signal, you will use an oscilloscope, an instrument that allows for the precise measurement of electrical signals detected by our system – a humble electrocardiogram. Before moving on to the next steps, work with a volunteer to ensure your circuit is correct, then ¡turn on! the power supply and the oscilloscope.
Step 9. Connect an oscilloscope to the output
- Using a BNC-to-splitter cable, attach the BNC-end of the cable to the Channel 1 terminal of the oscilloscope
- Using the same cable, attach the black portion of the splitter to the reference post on the breadboard
- Connect the red portion of the splitter (the one with the alligator clip) to the loose wire with the system output
Step 10. Connect a participant to the inputs
- Attach two electrodes to the wrists of a (willing) participant
[Note: the electrodes are sticky, but not too sticky. So if one of them falls off, just replace it with another!] - Connect one of the electrodes via a 2m cable to one of the inputs of the instrumentation amplifier (loose wire at Pin 2 of the AD620)
- Connect the other electrode via a 2m cable to the other input of instrumentation amplifier (loose wire at Pin 3 of the AD620)
- Attach a third electrode, a “reference electrode” to an electrically neutral part of the participant’s body (generally a body part like your elbow or your ankle)
- Connect the reference electrode to breadboard’s reference post via a 2m cable
Step 11. Ask someone to let you measure their heartbeat
- Use the oscilloscope to observe the signal coming from the participant’s heart (it may require adjustment of the oscilloscope’s abscissa and ordinate scales)
Check in
- Can you think of a way to determine a heart rate?
- What is the participant’s heart rate (in beats per minute) right now?