I'm looking for some feedback on the feasibility of my design, as I don't have much experience in electrical engineering or Ardunio. I'm not worried about coding (as I done quite a bit) just the physical circuitry.
What am I trying to build is a basic impedance reader for cell culture work. My lab doesn't have one so I'm building one based off a paper I have using arduino for a simple impedance meter.
For the image, blue wire leads to Analog pins 1-4, except for the blue pin running to the white ground pin. The Green wire are running from digital pins 6-8 and connect to 3 of the four electrodes. The black wire are representing under board connections. Finally the red wires are the leads running to the electrodes for measuring the resistance in the cell cultures. The 4 electrodes aren't shown.
The circuit functions like, a voltage is passed through the cell culture and picked up by the electrodes, which is then passed down to the header where the red and blue wires come together. The resistors in the circuit give me a known resistance, so I can use the input voltage (3.3v), the voltage measured by the analog sensors, and the known resistance to calculate the impedance value of the cellular barrier in the culture. R2 = (V2*R1) / V2, which is based on the voltage splitting principle.
I'm going to be taking 6 measurements using the electrodes. I was planning on using the digitalWrite(low) function on two of the digital pins so they are grounds (0v) and digitalWrite(high) on the last pin so that it is putting out 3.3v (the board is a MKR Zero). That will get me 3 of the measurements I need, and so then I will swap which digital pins are set to low and high until I get all six measurements.
My question is will having the digital pins set as low (or ground) negatively affect the circuit?
That leads me to my next question. I am planning on running the resistors into a common ground. The resistors are not connected in any way before the rail to the common ground. In my mind, since I am reading one electrode at a time, using the common ground won't cause problems. However, since I have never done this I need to ask a dumb question.
Will the resistor layout in the image increase my known resistance to the sum of the total resistance of the resistors?
Your diagram does not make much sense. I think you want to measure the resistance as a function of the distance from the High pin. Then you need to float the pin that are not measuring.
If you put low in one of your sense pins, you will just measure zero, the way you want to connect them.
Remove the common ground connection, and connect the digital pins to each resistance independently. Those resistances (120 Ohm?) will limit the current to 27mA, a bit high for a digital pin (7mA limit). Try 1k.
At the moment I have only a vague idea of what your circuit is and even less of an idea as to what the answers to your questions might be. Please post a proper schematic.
We also know nothing about the electrodes you have, please provide details.
You need to learn the difference between voltage and current, voltage is a difference measured between 2 points, it does not 'pass through' anything. Current passes through.
I think you would be better off just trying your circuit out and checking to see if you get the results you want. I consider electronics to be a great hobby for trying things and learning from what happens. As long as you use low voltages, which cannot harm you, the worst that can happen is you burn out a few inexpensive components.
