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An opto-electronic sensor system for measuring seed spacing uniformity with different types of seeds is described in this paper. It consisted of a rectangular photogate block (124 × 92 mm) with 24 phototransistors (diameter, 3 mm) receiving light beams from 24 light emitting diodes (diameter, 3 mm) opposite them, a digital input/output board in a personal computer, and power supplies. The opto-electronic system was tested by comparing seed spacing measurements obtained from the opto-electronic system with measurements of the same seed spacings obtained from a grease belt test stand. The tests were conducted with different types of seeds including regular-pelleted (diameter, 3.8–4.5 mm), mini-pelleted (diameter, 3.2–4.0 mm), and medium- encrusted sugar beet seeds (3.2-3.6 mm in diameter by 1.8–2.6 mm in thickness), and pelleted chicory seeds (diameter, 2.8–3.3 mm). Results showed that the adjusted opto-electronic seed spacings were not significantly different from the same seed spacings measured with the grease belt test stand. The opto-electronic sensor system worked well to obtain 508 seed spacings with regular-pelleted and mini-pelleted sugarbeet seeds and pelleted chicory seeds. The opto-electronic sensor system missed two seeds and detected two “phantom” seeds out of 170 seed spacings with the medium-encrusted sugarbeet seed.