What makes you tick?
Within each individual muscle cell in our heart there is a difference of charge between the inside and the membrane. Ions start gushing out from the control node in the heart and into the resting cell, making this difference of charge decrease until the cell contracts. A moment later the ions flow back and the cell returns to it's resting state. This will spread like a wave through your heart, and is called a heartbeat!
While this wave of contracting cells is spreading throughout your heart, we can measure the difference of charge between the resting cells and the contracted cells as an electric potential, or voltage if you will. Amplifying this tiny signal and plotting this voltage on paper as it happens is basically the ECG -- the Electrocardiogram.
With the ECG you will be given a window into your heart so that serious abnormalities can be revealed. Patients can be examined with stationary equipment for a small period of time, and an analysis of the heart activity can indicate complications that should be thoroughly examined. However, abnormal heart activity in an otherwise perfectly normal heart might occur outside of the examination room.
The Heartbeat Logger is a portable device that that logs your ECG throughout the day and throughout the night, 24/7. While this certainly is nothing new, even as an open source project (see MobilECG), Heartbeat is a project that, aside being of personal value for me, is designed to be simple to use and understand, and might serve a purpose somewhere for someone.
Disclaimer: THIS IS BY NO MEANS A MEDICAL DEVICE. Use at your own risk.
Current status: Third revision arrived, awaiting time to continue.
The heart and the ECG
- System overview
- The analog front end
- The frontend's INA321 inamps
- The frontend's TSV634 opamps
- SAMD20 microcontroller
- Clock source
- User interface
- Measuring the battery
- Voltage regulator
- Battery charger