Science Buddies: "Ask an Expert"

My students couldn't get their circuits to normalize to the neutral solution. We checked the circuit several times, everything was set up correctly. We made sure the neutral solution was the correct pH. We tried adding more potentiometers, but nothing would make the pump shut off. Without this, the artificial pancreas has no feedback loop and is not a very accurate representation of the pancreas. Help would be greatly appreciated.

Hi casazzar,

I'm assuming that you are working on the project described here:

https://www.sciencebuddies.org/science- ... as#summary

Have you tried the pump troubleshooting steps at the following link?

https://www.sciencebuddies.org/science- ... creas#help

When adjusting the potentiometers, did you start with the one with the highest resistance (see step 11 under Testing the Artificial Pancreas Model)? The lower resistance potentiometers may not have enough range to shut off the pump.

Was the conductance sensor immersed in the neutral solution as shown in figure 11 during normalization attempts?

Although the circuit is not terribly complex it is very easy to make incorrect connections on the breadboard. You might want to try rebuilding your circuit while following the step-by-step instructional slideshow provided in the procedure section of the project.

I hope this helps. Please ask again if you have more questions.

A. Norman