The soil nutrient rapid tester is one of the earliest devices developed based on the color box's qualitative color analysis system. It was first created by Henan Agricultural University as early as the 1970s. The L&Vngte Speed Tester uses a powder reagent instead of liquid, significantly extending its shelf life. This type of qualitative analysis is commonly used in flower cultivation, fruit trees, gardens, and greenhouses. However, the sensitive electrode in traditional soil nutrient testers tends to be unstable. If not stored properly, it can easily degrade. In contrast, the rapid soil nutrient speedometer using FET-sensitive membranes offers long-term stability and performance, though it is still in the research and development phase.
The most common method for accurate soil nutrient determination is chemical analysis using a photoelectric colorimeter. The key challenge lies in making this portable and suitable for use in rural areas, rather than just in laboratories. This is our preferred solution. From Changlang’s perspective, with the advancement of testing technology, physical testing methods are gradually replacing traditional chemical analysis. For example, the chlorophyll nitrogen analyzer developed by Spectruril shows great potential. When combined with GPS systems, its application becomes even broader.
The author believes that the soil nutrient rapid tester is different from general testing instruments. Soil testing speed is not only about the instrument's speed but also the efficiency of sample preparation. Similarly, the cost isn’t just about the device itself, but also the time required for the entire testing process. Therefore, we see the speedometer not only as a specialized photoelectric colorimeter, but also as a carrier of low-cost, rapid measurement technology and a complete set of soil testing equipment. Only when the speedometer is affordable and practical can it truly serve rural communities.
To develop an effective soil nutrient speed measuring instrument, we have studied related technologies both domestically and internationally. We have designed a device based on the photoelectric colorimetric principle, aiming to solve several key challenges: low cost, monochromatic light generation, light source selection, power supply design, colorimetric tank construction, light protection, moisture measurement, portability, and integration with fertilization recommendations and support systems.
The soil nutrient rapid tester employs microprocessor technology, particularly a single-chip computer with ashEPROM containing A/D conversion. This ensures high performance at a low cost and allows for easy interface between the display and keyboard. The system mainly detects photoelectric signals, which are slow-changing, so a high sampling rate is not necessary. Thus, the A/D 7135 converter is suitable for this purpose. We also use a 128×64 LCD (33) display, capable of showing four lines with eight characters each, totaling 32 characters per screen. The number of keyboard keys can be adjusted based on the design needs. Additionally, the system includes address decoding, clock, reset circuits, and other essential components for a basic microprocessor setup.
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