Crop density measurement is one of the most important factors in precision farming and effect on
the performance of harvesting machines such as combine and mower. So, the purposes of this study
are to design, build and calibrate of an inexpensive and non-contact instrument that can estimate
crop density for crops such as wheat, barley and alfalfa stems. The sensing unit is consisted of laser
transmitters, LDR receivers and AVR microcontroller used as register and data processing unit.
Experiments were done on Polystyrene plates for alfalfa and barley stems. The LDR receivers
receive the reminder of the laser light which passes through the crop stems and with using analog to
digital converter in the microcontroller data was stored on internal memory of micro and displayed
on the display. Total LDRs voltage was used as an indicator of density estimating. This voltage is
proportional to the density of the crop stems and the results of the voltage measurements show a
correlation of 0.93 to 0.98 percent between the voltage and the value of alfalfa density and R2 = 0.9
for barley. Ambient light was a factor that affecting the amount of voltage and to eliminate this
effect, receivers were placed in a protective aluminum box. This method has the potential of
estimating on the go measurement of various crop densities.