"Non-inspection report" of 1N4148 diode and another characteristic of LED

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.
Let's take a look at the "Nuclear 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 of things, I won't be arrogant. . . 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.
After looking up the information, it is clear later that the 1N4148 diode is about a temperature rise of one degree Celsius, and its forward voltage drop is reduced by 0.003V (3mV). If you connect 5 1N4148 in series, the forward voltage drop will decrease by 0.015V (15mV) for every degree of temperature increase. The more you string, the more change, and the easier it is to detect the change. It’s really “Hanxin’s string diodes, more and more good”.
However, everyone must also pay attention to the so-called "objects must be reversed", if you string too much, you will be finished. Because the turn-on voltage of a section 1N4148 is about 0.7V (it seems to be). So, if you string too much, the turn-on voltage of the diode group exceeds your supply voltage, and you are terrible. Because the diode group can't be turned on at all, it can't talk about temperature measurement. . 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. . .

led

LEDs are beautiful, aren't they? But don't think that LEDs will only shine. It is also a diode and it can also be used for temperature measurement. However, I strongly do not recommend that you use a light-emitting diode to measure temperature. LEDs also have an unknown feature. It is also very "sensitive."

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.