I am not a medical professional. Construct and use this device at your own risk. Introduction:
In this instructable I will demonstrate how to make an electrocardiograph (EKG) for monitoring your hear rate via leads taped to your skin. The output will be used to switch an LED on and off with each detected heartbeat.
All circuit components can be found at Radio Shack. The total cost of this project is around $30.
Estimated completion time: 5 hours
This project may be too difficult for anyone unfamiliar with the operation of a multimeter and its use in basic troubleshooting of electronic circuitry.
- Biofeedback: Learn to manipulate your heart rate at will and monitor its reaction to your
thoughts and behavior. Wikipedia: Biofeedback
- Relaxation: Focus on bringing your heart rate down when stressed. The rest of your
body will follow suit.
- Decoration: Can be integrated into a costume. Pulsing Iron Man arc reactor anyone?How it works:
This circuit detects and amplifies the electrical impulses generated by your heart with each beat. Your skin acts like a giant antenna, picking up a lot of noise and interference so a differential amplifier is employed to effectively cancel any unwanted input.
The differential amplifier has two inputs relative to a common ground. Any voltage that is common to both inputs will be effectively ignored while any difference in voltage between the two (i.e. the polarization of your heart muscles) will be greatly amplified.
I will be using this device for biofeedback and ornamentation so I will not be exploring all the complexities of an EKG output. However should you wish to see an EKG in all its glory, the output of the differential amplifier portion of this circuit can be connected to an oscilloscope and should permit you to see (untested) all the features one would expect. However, as a commenter mentioned one should never connect an amateur circuit that is connected to your body (particularly your heart) to your household power lines. If you wish to employ an oscilloscope use a battery powered device or take steps to electronically isolate the circuit from the oscilloscope.
I just want a device that blinks every time my heart beats. To give clean pulse I have added a monostable timing circuit to the differential amplifier output that turns the signal into a square wave with an adjustable width.
More information that may be helpful in understanding the details of this circuit can be found below.Wikipedia: Differential Amplifier Wikipedia: ElectrocardiographScribd: Monostable Timing Circuit