Data acquisition from ECG module (3.3V) and HC-SR04 (5V) simultaneously

Hi everyone,
I hope everybody is feeling as good as possible during these challenging times.

I will need some help for a design project. I need to acquire data simultaneously from an ECG module (AD8232 from Sparkfun) and from the ultrasonic sensor HC-SR04.

This is the first time I attempt measuring two signals at the same time (analogic signal from AD8232 and digital from HC-SR04) with an Arduino Uno.

I had a meeting planned at my school with a member of the electrical engineering department, but everything is presently closed and will most likely remain closed until the end of the semester.

I will therefore need your expertise with arduino boards to complete the wiring of my project.
Here are my questions. I will try to make this as clear as possible, but please let me know if some information are missing.

1.a) The AD8232 PCB that I’m using is powered with 3.3V while the HC-SR04 uses 5V. Can I simply connect AD8232 to the 3.3V pin and HC-SR04 to 5V pin and expect the voltage in each sensor to respect 3.3V and 5V at all time ? For my safety, when I will connect the electrodes to my body, it would be great if the voltage could never exceed 3.3V in the AD8232.

1.b) If I use both 3.3V and 5V pins of the board simultaneously, will it affect the precision of my analogic reading coming out of the AD8232 module ?

  1. Should I ground both sensors to the same pin or use two diffferent GND pins from the board. I read a few threads in which people had different results depending on which way they grounded their sensors.

The basic idea is to find a correlation between a heart beat and the respiratory rate. I will use a laptop (not plugged to the wall for safety). The arduino Uno will be powered and data will be transfered from a 2.0 USB port.

I attach to this post a schematic of my circuit which I hope will help you understand the questions above.
I have a bioengineering background and so my background in electronic circuit is quite low. Please let me know if there is other information I need to provide to make the questions clear. Any help will help!

Stay safe and thank you.

ECG circuit.png

Can I simply connect AD8232 to the 3.3V pin and HC-SR04 to 5V pin and expect the voltage in each sensor to respect 3.3V and 5V at all time ?

Yes.

For my safety, when I will connect the electrodes to my body, it would be great if the voltage could never exceed 3.3V in the AD8232.

Believe me, the 5V wouldn't harm you too.

1.b) If I use both 3.3V and 5V pins of the board simultaneously, will it affect the precision of my analogic reading coming out of the AD8232 module ?

Usually not.

  1. Should I ground both sensors to the same pin or use two diffferent GND pins from the board. I read a few threads in which people had different results depending on which way they grounded their sensors.

These are very seldom cases where it matters to which GND pin you connect an external circuit. In the majority of all cases you can use any GND pin and connect as many boards as you wish to the same GND pin.

Alright that's good to know ! Thank you.