Science Buddies: "Ask an Expert"

Hey everyone

I'm working on an artificial pancreas model, but I've been facing some issues in choosing the appropriate materials that are also available where I live. The project uses a 5-6 V peristaltic liquid pump with motor current 500 mA. This pump is unfortunately not an option for me but I found a mini submersible water pump 3-5v with 180 mA current. I also found an R385 DC 6-12V pump with 500-700 mA current. The project also uses an IRLB8721 transistor that is unavailable where I live. These are the available transistors: 2N7000, IRFZ44N, IRFB3607, IRF840, IRF830, IRF730, IRF640, IRFP260N, IRF530, IRF3710, IRF1010E, FDA50N50, IRFU9310, FDA24N40, 12N60, IRF520, IRF3205, IRF9530, IRFP250N, IRFP150, IRF740, IRF4905, IRLZ44N, IRF9540, IRF540.

My questions are: can I use on of the 2 pumps I listed instead of a peristaltic one? Which of them is the best option? Would I have to buy extra materials or change the transistor if I use the 12v pump? Also would I have to change the materials for the submersible one? And which transistor can I use instead of IRLB8721? Would I need any extra materials if I use a different transistor?

Thank you all in advance

Hi,

Technically "any" pump will work with this project as long as you have a compatible power supply and transistor. The Arduino can only provide 5 volts and up to a few hundred milliamps, so for the first pump you listed (3-5V, 180mA), you could power it directly from the Arduino as shown in the project procedure. The 6-12V pump would also work but you would need an external power supply, such as a 4xAA battery pack (6V) or a 12V wall adapter. We have several Arduino tutorials that would help you do this, such as:

https://youtu.be/To3DKP99-1U (specific to pumps, see the part around 6:40 about external power)

and

https://youtu.be/I7MrL5Q7zvY (more general about how to power Arduino projects)

Regarding the transistor, if you want to follow our wiring diagram exactly, pretty much any N-channel MOSFET will work for this project as a substitute. You can find the datasheet for any of the parts by googling the part number plus "datasheet". For example here is the datasheet for the IRFZ44NPbF:

https://www.infineon.com/dgdl/Infineon- ... 3b3a9f220d

The datasheets contain a ton of information, but if you just glance at the information in the "absolute maximum ratings" table on the first page, you will see that this transistor can handle WAY more power than either of the pumps you listed needs - up to 49 amps! That is enough to run a large motor, so it is fine for this project.

The only other thing you sometimes need to look up for Arduino projects is the "gate threshold voltage" on the second page - the minimum voltage applied at the gate required to turn the MOSFET on. In this case it gives a range of 2-4 volts, which is fine because the Arduino UNO uses 5 volt logic. Some other Arduino models and microcontrollers use 3.3V logic, which may not be enough to turn that MOSFET on, so you'd need one with a lower gate threshold voltage. So assuming you are using an Arduino UNO or equivalent, you do not need to worry about that for this project.

Finally - make sure you buy an N-channel MOSFET and not another type of transistor like a BJT. They can also be used to control pumps/motors but the wiring is different and would not match our diagrams exactly.

Hope that helps! Please write back if you have more questions.

Hey!

Thank you so much, your response has really helped!

Regarding the mosfet, would it be better to use the IRFZ44N or the logic level option IRLZ44N?

Also, would it be possible to first program the whole project and then power it using an appropriate power source (I will be using the 3-5 V pump) and run the project in the science fair without being connected to a computer? Unfortunately I'm trying to sort it out but my school has really strict policies on electronics

Thank you so much!

1) For this project I don't think the IRFZ44N vs IRLZ44N is going to make a difference. Looking at the datasheets, the IRFZ44N has a gate threshold voltage of 2-4V and the IRLZ44N is 1-2V. So as I mentioned before, if you were using a lower-voltage microcontroller then you'd want the IRLZ44N but if you're using an Arduino UNO which operates at 5V then it doesn't matter.

2) It is possible to disconnect an Arduino from a computer and run it either on battery power or a wall adapter after you have initially updated the code. The code will still start automatically anytime the Arduino is powered up or you hit the reset button. We have a video about powering Arduino projects that you may find useful here: https://youtu.be/I7MrL5Q7zvY?si=0bLphzJ-fyf2uE0E

3) If for some reason you cannot bring your Arduino at all, you could ask if you could show a demonstration of the code in Tinkercad Circuits. This is a free online Arduino/circuit simulator that runs in a web browser and we use in many of our projects. The disadvantage is that it only has certain parts in the online library, and it will not have the "conductivity sensor" used in this project, and there will be no way to simulate pouring liquid. But for example you could replace the conductivity sensor with a potentiometer and use that to demonstrate the automatic on/off behavior of a DC motor (there is no "pump" in Tinkercad, but the wiring of a DC motor is the same). We have a tutorial about Tinkercad Circuits here: https://youtu.be/9RF_BZ1Cg4k?si=t-aG8bm3iXWqerKK

Okay!

Thank you so much for everything!

You're welcome! Please let us know how it goes.

Hey!

I'm so sorry for the amount of questions but I ended up buying the 3-5 v pump. As I was about to make my model, I noticed that the exposed metal ends of the wire are really thin and tiny, and I'm afraid that the Alligator clips will break the wire, but I also don't have any soldering tools or experience. What do I do? I'll attach a photo of the pump below.

Thank you

Hi - your picture of the pump did not come through, but you should be able to connect to it without soldering. The alligator clip teeth may look sharp but they are not designed to literally cut through wire. If you cannot get a good grip on the exposed ends, you can strip some insulation off the wire to expose more metal. We have a tutorial about how to do that on this page (scroll down to the section about "hookup wire"): https://www.sciencebuddies.org/science- ... g-tutorial