Design and development of low-cost grain moisture meter for smallholder farmers

Abstract:

Smallholder farmers in the arid zones of northern Kenya routinely face a 6 to 11 per cent price penalty at the grain market because they cannot measure moisture content of the produce at home. Commercial moisture meters are priced between KES 15,000 and KES 65,000, which puts them outside the reach of farms below five acres. This research presents the design, fabrication and field evaluation of a capacitance-based grain moisture meter with a bill of materials below KES 2,500. The meter is built around an ATmega328P microcontroller, a parallel-plate copper sensor, a 10-bit ADC stage, and a 16 × 2 liquid crystal display, all powered by a 7.4 V rechargeable lithium pack. Calibration was carried out against the oven-drying ISO 712 method for six common grains of the East African drylands - wheat, pearl millet, sorghum, mung bean, pigeon pea and cowpea - across six moisture ranges. The meter achieved a mean accuracy of 96.3 per cent, precision of 98.1 per cent and response time of four seconds. Calibration curves were stable over six months of continuous use under field conditions. The unit weighs 380 g, operates for 45 days on a single charge, and can be re-calibrated through four push buttons on the front panel. Deployment on 40 smallholder farms in Nakuru County between November 2022 and April 2023 demonstrated an average reduction of 7.4 per cent in post-harvest price penalty. The meter therefore offers a practical, affordable alternative for grain moisture assessment at the farm gate.