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I want to create some project which uses an Arduino to collect and display ECG data. It uses two electrodes which are attached to the body (on the chest). The signal is then transmitted through op-amps to an Arduino ADC pin. The Arduino is connected just to a PC. Is it safe for both the human and the Arduino board to be connected this way?
Should I make some safety pracautions and if so, which?
It's not advisable unless the entire project is low voltage and battery operated. Anything mains operated could be dangerous even if transformer isolated. There are specific safety requirements for mains operated patient attached equipment to protect against excessive leakage currents and potential safety hazards due to equipment or component failures.
Those regulations apply to professional medical equipment, but they are there for a reason. You shouldn't assume that it's safe to ignore them even if it's just a hobby project.
When doing an ECG test, the electrodes are much more conductive than dry skin, so the possibility of triggering fibrillation or other arrhythmia from small voltages is present and needs to be taken very seriously. Most pacemaker pulses for implanted pacemakers are from 2mV to 250mV. That's not a whole lot of voltage, and if your device accidentally drives that to the heart, you could be in a great deal of trouble.
Short answer: Read IEC 60601-2-25.
Medium answer: To do it these days, you need to have all your digital signals opto-isolated across a physical isolation boundary, and your power source has to be isolated (i.e. transformers). There are very detailed and strict requirements on what kind of protection those need to be capable of, which involves being able to withstand being zapped with many kiloVolts and not crossing the boundary.
All your amplification and data processing needs to take place upstream of your isolation boundary, with basically nothing but a UART crossing it. In short, you basically have to make a custom PCB to do it properly.
Use something like the TI ADS1298 as an analog front end, which you can communicate to through SPI.
You are not going to be able to read ECG signals with the on-board A/D, it does not amplify enough or have enough common mode gain rejection. You are going to have to use an instrumentation amplifier. With proper design (opto-coupler) it should be fairly safe to connect a battery powered instrumentation amplifier to an arduino, at least that is how I would do it. (I would wall power the instrumentation amplifier, but I'm a risk taking idiot)
It is safe if you connect Arduino to the laptop and run it only using batteries (then the highest voltage that could shock you is the laptop's battery voltage - that should be safe enough).
I made a similar project some time ago using different parts - I chose to power the whole device from batteries and use Bluetooth to send data to the computer.
The easiest, and safe, design would be to use a battery powered amplifier to amplify the electrodes signal, connect the amplifier to a battery powered Arduino to capture, process and store the information.
After disconnecting the electrodes from the patient, connect Arduino to PC any way you want (can), and transfer the data to the PC.
Obviously, you don't use this apparatus on anyone that has (wears) a "pace maker"!
