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2) Each unit can counter up to 3 frequency bands simultaneously, each frequency band is separate and with adjustable power from max to off (0).
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In the P0 port of the 51 MCU, when operating in normal IO mode, it functions as a quasi-bidirectional port. However, when the second function is activated, it behaves as a standard bidirectional IO port. For such ports, both high and low output levels are required, typically achieved using a complementary push-pull configuration.
The second function of the P0 port employs this complementary push-pull structure. What exactly is a complementary push-pull? Below is a simplified equivalent circuit to illustrate the concept.
When the P0 port is used as an output in its second function, two switches, K1 and K2, alternate between being turned on. When K2 is closed, K1 is open, resulting in a high-level output. This provides strong driving capability due to the low resistance of the electronic switch (much lower than that of a pull-up resistor). Conversely, when K1 is closed and K2 is open, a low-level output is produced.
These two switches operate in a complementary manner, with one "pushing" current and the other "pulling" it. Hence, the term "complementary push-pull." This design offers significant advantages, including strong driving capability and stable performance. However, it also presents challenges. During level transitions—such as from low to high—it’s crucial to avoid both switches being on simultaneously, which could cause a short circuit. Proper timing control is necessary to ensure safe operation.
For input operations, the bidirectional IO port enters a high-impedance state. This means the port has a very high internal resistance, making it insensitive to external signals unless actively driven. In this mode, the port can act as a sensitive input without interfering with connected devices.
What does a high-impedance state mean? Imagine the microcontroller's IO pin as a voltmeter with a very large internal resistance—like 100MΩ. This high resistance allows the pin to detect external voltages without significantly affecting the circuit it's monitoring. If you touch the pin with your finger, which has a relatively high resistance, the measured voltage may fluctuate slightly due to electromagnetic interference or even body capacitance.
This floating input state can lead to unpredictable readings. Even without touching the pin, changes in the surrounding electromagnetic field might affect the reading. Later, we'll conduct an experiment using the 51 MCU to observe how the P0 port behaves in this high-impedance state.
Why is high impedance important for input? Let's consider a scenario where an external device drives the IO pin. If the device has a high output resistance, it may not be able to drive the pin effectively. A high-impedance input ensures that the microcontroller doesn't interfere with the device's output, allowing accurate signal detection.
To experience this, we can write a simple program. The code sets P0.0 as a high-impedance input and connects an LED to P1.0. When the program runs, the LED should reflect the state of P0.0. However, since P0.0 is floating, the LED's behavior will be unpredictable.
In practice, the LED might remain lit because the P0.0 pin isn’t truly at a high impedance but rather has some residual capacitance or leakage. Touching the pin with a finger or connecting a high-value resistor between P0.0 and VCC can change the LED's state. This demonstrates the sensitivity of the high-impedance input.
Note: Individual differences in skin resistance may affect the results. If the LED doesn’t respond, try using a 100kΩ resistor instead of a finger. Also, ensure the program is correctly implemented and the development board is properly set up. If the LED remains off initially, try grounding the pin with one finger and touching it with another to observe the change.
1) Output power total 150W, Use High gain 5-6dBi for each omni antenna, shielding 500-1000m,Still depends on the strength signal in given area.