The electric field imaging device MC33794 is a product introduced by Freescale Semiconductor in 2003 and can be widely used in non-contact physical detection and measurement.
The sine wave generator cooperates with an external load resistor to generate a pure sine wave of 120 kHz. When the electric field of the electrode changes, the corresponding capacitance value changes, and the measured voltage is proportional to 1/C, that is, the detected voltage is decreased by increasing the capacitance. small. The VPWR positive power input pin, which is connected to a 12V supply, regulates this voltage to 5V (VCC) and 8.5V (VDD) to power the MCU and other external components.
The MC33794 has a capacitance measurement range of 0pF to 100pF. When using an 8-bit ADC, the resolution is 0.4pF. When using a 10-bit ADC, the resolution is 0.1pF. As can be seen from Figure 3, the MC33794 is very convenient to use, and only a small amount of external resistors and capacitors can work. At the same time, the MC33794 does not require high MCUs. It only requires an 8-bit ADC and a general-purpose interface.
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