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Homemade Field Measurer
Instead of paying up to $400 for an acreage counter or field measuring device Minnesota farmers Loren and Earl Ingebretson, of Felton, developed their own inexpensive model for about $20.
The Ingebretsons, whose idea was a "Sugarbeet Growers Ideas Contest" winner, say you need the following items to rig up your acreage meter an inexpensive hand calculator, double strand speaker wire, and a magnetic reed switch (get the "closed" model which is available in electronics stores). You also need an old wheel weight, a magnet, a quick coupler for disconnecting the wires and an ohmmeter.
Loren notes that he used a Radio Shack EC-203 calculator but that many other models will work just as well. He suggests avoiding the very thin calculators as they don't have a lot of room to work in.
To begin, you remove the back of the calculator and find the terminal for the (_) button. You find this by depressing the (=) button and using the ohmmeter which will show a reading when the probes are placed on the correct terminal.
Next solder one strand of the double strand wire to each terminal post. Also, melt or punch a hole in the back cover for the wire to exit. To this wire fasten the quick disconnect coupler, to which you attach a longer section of wire that runs to the reed switch. The coupler makes it easy to remove the calculator for other uses.
Next, connect each lead to a terminal of the magnetic reed switch. To test the switch, turn the calculator on and push the (+) button. When you pass the magnet past the switch, the number should blink,counting it the first time. Each pass of the magnet past the switch should add the number again.
The Ingebretsons mounted the calculator on the handlebar of their 3-wheeler, fastening the reed switch to the left fork and mounting the magnet on a wheel weight secured to the wheel rim.
The Ingebretsons use the system on their 3-wheeler to measure distances but you can also modify the system to fit on planters, drills and other implements to measure acres covered.
To do this, attach the magnet on a ground driven shaft on the implement and mount the reed switch so the magnet will pass it on each revolution.
The constant to punch into the calculator will be the result of width the implement covers (in feet), times distance covered in one revolution of the shaft (in feet), times .000023 (translation of a square foot as a fraction of an acre. An acre equals 43,560 sq. feet).  `

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1984 - Volume #8, Issue #4