Science Buddies: "Ask an Expert"

I'm attempting to make a simple audible compass for a blind friend of mine. Using the ability to sense the color red to play a sound when the compass is facing North.

Using this project
Is It Ripe Yet? Build a Circuit to Detect Ripe Produce
https://www.sciencebuddies.org/science- ... pe-produce
I was working on the "Build a Circuit to Differentiate Red and Green Produce" section and was looking at the N Channel MOSFET listed as STMicroelectronics STP16NF06L MOSFETs Transistors.

I have ordered some and they will be here someday, but I was wondering if any of the MOSFETs I have might do the job while experimenting, at least till they get here.

I have:
IRFZ44n
IRF530N
IRF540N
IRF640N
IRF740N
IRF840N
RFP30N06LE
2N7000
IRF3205
IRF9540

If any of those will do I'd appreciate a confirmation. I feel like IRFZ44N should do the job but its been quite some time since I've worked with these kinds of projects and I'm pretty rusty.

Once I have things sorted out there I eventually plan to use a 9V battery for its compact nature. I believe I can accomplish that by changing the resistors from 120 to 225 (or there about) again, I'm quite rusty and if none of the experts here are able to confirm that or send me on the right direction I'd appreciate it.

Thanks for your time and assistance.

Hi!

Using the IRFZ44N transistor is a great choice because this transistor is good for higher voltage situations/motor control. Let me know if this matches the specific details about the project, and we can go from there.

As for the question about the resistors, switching to 225 (or 220, even) is a great choice because it helps limit the current more, especially since you’re using the 9V battery. In fact, depending on how you want to prioritize battery life, you can use

Hi Snehaarun,

Thank you for confirming I was on the right track here with my alternate transistor choice as well as what I thought was needed for the 9v battery.
It seems like you got cut off part way through some advice you were giving.

"In fact, depending on how you want to prioritize battery life, you can use"
I would love to hear what suggestion you have for increasing battery life as that would be appreciated.

For reference in how this device would be used by my blind friend. While navigating he will occasionally lose which direction North is. The idea is that this could be in his pocket or bag and when he loses his reference point he would take this out, swap it on. Orient himself to North, then put it away. So it should only be used in short bursts here and there.
Any recommendation on a way I could get a longer battery life while keeping this compact would be very helpful.

To start this I'm using the body of this one I found at Walmart.

That was the only compass they had at walmart but I was able to take it apart and I think I can house most of the components in the base.

Again, thank you for your time and assistance.

Please note that these forums are for K-12 student science and engineering projects. Our Experts are not able to help with projects outside of this, and we recommend using other general forums online.

Amy
Science Buddies

Oh, I'm sorry. I was unaware of that. I was just working off one of the projects on your websites that almost perfectly matches the info I needed and had a few questions. I'm not intending to make this a product of some sort. Just found a project that looked like it could help fill one of the needs my friend has and thought the best place to ask would be where it was posted.

I appreciate the help I received so far, I think that answers all my questions I was just curious about the rest of what the previous answer was saying about making it more efficient.

Absolutely! And I think this is a great project and adaptation of the student project. I, too, am curious what Snehaarun was going to add, since it does appear that something got cut off. Hopefully they will post an update soon.

I hope all goes well with your project. I'm sure your friend will be grateful for the custom assistive device!

Amy

Thank you, once I do get it working I'll post it here with any modifications I make since it is hopefully something that could be useful to others as well. Could also be a fun project for students to make.
Have a great day Amy.

Hi!
I was meaning to add that if you wanted to prioritize a longer battery life, you might want to consider switching to a resistor with an even higher amount of Ohms — such as 470 Ohm resistor. In this way, if you could also optimally use an LED as part of your circuit. (Let me know if you planned to have the red color as part of your circuit in any other way.)

That makes sense, thank you for the follow up.
I only plan to use 1 Red LED to reflect off of the N indicator on the Compass and use a small speaker to indicate when they are facing North. I'll keep the Potentiometer how its used in the project so that it can be calibrated if needed.