The diode is not known as the "sensitive" side

When lifting the diode, everyone generally thinks that it has a "single-directional, reverse-off" "spleen temper", so it plays an important role in the circuit. Some people also use the reverse voltage drop of the diode just for the regulator.

However, diodes also have a side that is not known to be "sensitive." This made him even more mysterious.

A diode is a sensitive body that is quite sensitive to temperature and heat. The common level of the 1N4148 diode can already be described as "pick up". Here, we take it as an example to introduce its "sensitive" characteristics.

Let's take a look at the "Medical Report" of the 1N4148 diode:

Reverse recovery speed: super fast less than 0.000000004 seconds (4 nanoseconds) forward withstand voltage: lower about 100V reverse withstand voltage: lower about maximum forward current: about 0.2A... there are a lot, I will not Luo Hao. . .

As can be seen from the above, the 1N4148 is a low current, high frequency switching diode. But we just take him to measure the temperature, it doesn't matter if the current is big.

We then analyze the specific feasible solution on the microcontroller: here we take STC12C5A60S2 as an example. The STC12C5A60S2 is the most powerful person in the STC 12C series, and the configuration is the most advanced. Including the AD conversion we are going to talk about today. The AD conversion of this MCU can reach 10 bits, which means that a total of 1024 different values ​​can be output, that is, 0~1023.

Then probably calculate, 5000mV/1024≈4.88mV, which means that the AD conversion of the MCU can only detect the change of 4.88mV. If the change is less than this value, it may not be detected. So we have to connect at least two diodes in series. This is at least, if you only have one string, then the accuracy of this thermometer can't reach 1 °C. This precision is indeed worrying. . .

I am afraid that the idiot knows that the positive pole of the LED is connected to the positive pole, and the negative pole is connected to the negative pole. It will definitely emit light. The reverse connection will definitely not emit light, because it is also a diode and also has unidirectional conduction characteristics. But you may not know that there is an unknown use when the LED is reversed - like a photoresistor, it can also meter.

We also take STC12C5A60S2 as an example to give an introduction. Metering is performed with two I/O ports: the IO port on the positive side of the LED is set to high-impedance input, and the push-pull output is set on the negative side, and the level is pulled high.

At this time, a miracle occurs. The level of the IO port of the high-impedance input changes like the ambient light. When the light is bright, it is high, and when the light is dark, it outputs low.