The paper presents the results of comparative laboratory tests of three types of photoelectric sensors used for the control of seed sowing. The study aimed to determine the grain counting errors in terms of uneven dosing of wheat grain that occurs in row drills and single seeders in repeated sowing process. Grains were administered one by one at regular intervals and also in double or triple passes. A measure of the accuracy of the count is called visibility factor Pn, defined as the ratio of the number of counted seeds to the number of sown seeds. For individually dosed grains the visibility factor Pn the highest number was reached by the sensor III, while for wheat grains dispensed in triple passes, sensor II and III reached a similar rate of visibility factor (PnII = 79.2; PnIII = 77.5). Further studies are planned for other types of grains such as small canola grains to verify the usefulness of the sensor built on the basis of the image sensor.