soil content measurement circuit

 The soil content measurement circuit directly measures the water content, salt content, nitrogen content, pH, etc. of the soil in different areas, which
is of great significance to soil improvement, the growth of various crops, and guiding farmers to farm scientifically. The soil electronic measurement circuit introduced in this example can quickly and accurately test
the specific conditions of soil and fertilization. It is a relatively new and practical agricultural electronic measurement circuit.
    (l) The composition of the soil content measurement circuit is shown in Figure 8-25. The soil content measurement circuit consists of 8098 programmable monolithic module, two
8255 programmable peripheral interface circuits, 6264 static random access memory, 2764 ROM class memory, 74LS373 8D latch circuit,
7650CMOS high impedance input operational amplifier, CA3140 high impedance input It is composed of operational amplifier, NE555 time base circuit and 7218 driver integrated circuit
.
    (2) Measurement of various contents This circuit can measure various physical and chemical data in the soil, including: ammonia, phosphorus, potassium content, pH
, salt content and moisture content, etc. Among them, the electrode potential measurement method was used to determine the soil rpH value and available potassium . The potential difference of the electrodes is determined by
the concentration of ions in the solution. The signal is sent from terminal A in the figure to the high-impedance CMOS operational amplifier 7650. In this way, the input impedance of the measurement circuit
matches the electrode. The signal input from the 7650 non-phase input is amplified and output from the ⑩ pin, input to the 8098A/D terminal of the programmable module, and
the result processed by the 8098 is sent to the display. The Do~D7 terminals of the drive circuit 7218 drive the display screen to display the measurement results.