Magnetic reed switch from Radio Shack

I just thought i would post this because it is a very useful switch.

They sell them at Radioshack for $5, i could not find it on their website but i did buy one so i know that they sell them.

Have you ever needed to use a limit switch but did not need/want the switch to contact with the other part well now you can. The reed switch turns on when it is in close proximity (3/4in or less but it can be increased with more powerful magnets) to a magnetic field. Its works very well and everything is 1/4in in diameter so you can easily mount these in holes.

I plan to use these on robots to determine when two parts are to close together before they collide with each other. I also have some other ideas for its use, if you were to drill a small hole in one of the large wheels and put a small magnet in it you could mount a reed switch on the base so that it lines up with the edge of the wheel. Then when the wheel spins your program can add 1 to a variable every time the wheel makes one rotation in 1 minute which will give you the rpm.

That is a cool way to measure rpm but a shaft encoder could do that same although i think that in some cases this is the only thing small enough to fit in an area.

Here is a picture

Great idea! Post a pic of what you do with it!

I am going to build a small rig with like 6 motors and a 10 to 1 gear ratio that will drive a wheel with a magnet in it.

I am going to have the robot calculate the speed and rpm in 1 minute and then report the data back.

This is just a very interesting way to find the rpm, the encoders get old after a while so this is just a new way to find the rpm and speed.

Alright, i finished building the rig and it spins a wheel anywhere from 0 - 500rpm.

I have not programmed it to record the data and report rpm back but i have used a simple program to spin the wheel and print the switch state onto the screen.

I was able to get back some very important data.

This switch cannot operate with accuracy above 100rpm with the provided magnet, if you use a much stronger neodymium magnet it might work at higher speeds.

The reason that it won’t work is because the switch does not stay within the magnetic field for long enough to open the switch.

I tested it at very low speeds and the switch worked flawlessly turning on every time the wheel rotated.

Here are some pictures