Magnetic Reed Switches

dhmai · Post by **dhmai** » Mon Oct 25, 2004 1:46 pm

Hello, My name is David Mai and i have a problem. I have some magnetic reed switches and i need to find a way how to stretch a signal reading. I put a part of a the switch on a part of a bicycle and the magnet on the wheel. I need to find a way when I keep pedaling on the bicycle that it would would always sense that the wheel is constantly moving instead of it sensing everytime the magnet passes by the sensor.

shijun · Post by **shijun** » Wed Oct 27, 2004 5:25 pm

Hi Dhmai,

This is an interesting experiment. Are you doing this project for a science fair? My question is: why do you need to know that the wheel is constantly moving? Your sensor only detects the signal when the magnet passes by, which is actually adequate for measuring the speed (if that's what you are after). Have you learned about angular velocity and angular acceleration? You can then convert it into linear speed if you choose.

But first tell me what you are trying to do.

Shijun
Science Buddies Staff

dhmai · Post by **dhmai** » Thu Oct 28, 2004 1:30 am

The thing is that the wheel is always moving, but not at the same speed. For an example, a person on a bike would pedal at rate about 20 mph. After a while, the person would slow down less than 20 mph.

What i am trying to do is similar to making the speed rate of the wheel like an acceleration button trigger on a controller. When the bicycle is pedaled backwards, it would trigger a deceleration button.

Sorry if i sound confusing and vague.

shijun · Post by **shijun** » Thu Oct 28, 2004 4:44 pm

Well, it depends on how fine a "resolution" you want. In other words, how fast would you like the apparatus to detect change in angular velocity (or acceleration in other words)? Do you think having multiple triggers along the wheel would help? Why or why not?

Shijun