Tired of waiting three or four minutes for his handheld grain probe to settle on a temperature value, Fife farmer John Hutcheson went in search of some permanent alternatives and has been crowned winner of the Farmers Weekly Inventions Competition simple category.

Off-the-shelf options already existed, but, at £42 a pop, they were too expensive to justify stationing at each of the farm’s measurement points.

John’s solution was to find out how they worked and make some himself.

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Sifting through documents that came with the farm’s readout device revealed that the key component was a thermistor with a particular characteristic – essentially, the way resistance changes with temperature.

After carrying out a few tests on the handheld device, he worked out which type was required and ordered a batch online.

To make the probes, he soldered the thermistor onto one end of a length of wire and a 6.35mm audio jack onto the other, ready for the measurement device to plug into.

This assembly was then slotted into a length of 20mm electrical conduit, with regular cable glands and push-fit caps sealing off the ends to prevent grain getting inside.

Quick and cheap

The bits for one probe cost £5 and it took him 10 minutes to put together, making it easy to justify producing a large quantity.

With his portable unit, it often took the best part of a day to get around all of the farm’s stores, so having probes always at grain temperature has saved a huge amount of time.

Next, he plans to make a logging system so that readings are automatically recorded at regular time intervals for quality assurance schemes.