For quite a change from the normal pace of things arround here, I’ve decided it is finally time to add the “engineering” to this blog.
I’ve been wanting to weigh a book I have that I am considering selling so that I can calculate what shipping would be. However, I didn’t have a scale to weigh the book in and I wasn’t willing so spend $15-20 on a scale right now. So what does a guy with an electrical engineering degree do? Build my own scale.
Well, spring scales are based on a physics principle called Hooke’s Law, which basically states that the force that a spring exerts is linearly proportional to the distance it has been pulled or pushed. I had a spring that was used to hold the greenhouse door closed that has just been sitting arround after the door broke in high winds. So, I took the spring, the eyelet screw attached to the spring, one of several five-gallon buckets I have, and some twine and made myself a scale.
To use this scale, I had to calibrate it against a known weight. For that, I used two gallon jugs of water. A gallon of water is 8.35 pounds and using two of them gives me two data points from which I can get a linear equation that will give weight from spring displacement.
In the end, I got the book weight, which is just over three pounds. And the scale didn’t require anything more that what I had. I should be able to use this when I finally have a harvest to give me some idea of how much I get from the harvest.