In recent years, the increase of non-linear loads caused more harmonics on power systems. With the advent of the loads that are sensitive to power quality, harmonics are more important than in the past. Determination of those harmonics is required for the avoidance of problems. In this paper, a practical low cost harmonics detection system is designed and performance of the system is considered on single and multi-channel usage. 400th harmonic can be detected under 3.5 mu s over 8- channels using the developed device and processing software. Results show that proposed system can be used for a broad range of harmonics detection systems in real-time.