The product cannot be connected to the Internet, and the displayed time cannot be updated through the network. The LCD displays the date and time inaccurately. From which angles can it be solved...

QWE4562009

The product cannot be connected to the Internet, and the displayed time cannot be updated through the network. The LCD displays the date and time inaccurately. From which angles can it be solved... [Copy link]

 

The product cannot be connected to the Internet, and the displayed time cannot be updated through the network. The LCD displays the date and time inaccurately. How can this be solved? The RTC external clock is used, and the crystal oscillator runs at 32.768K (why not use other frequencies?)

dcexpert

32.768K crystal can take into account power consumption, cost and accuracy. For higher accuracy, a temperature compensated crystal is needed. However, even the best crystal will have errors over time and needs to be corrected by certain methods, such as radio waves, GPS, WIFI, etc.

QWE4562009

dcexpert published on 2021-7-3 17:21 32.768K crystal can take into account power consumption, cost and accuracy. For higher accuracy, a temperature compensated crystal oscillator is required. However, no matter how good the crystal oscillator is, it will have errors over time and needs...

The key is that there is no wireless transmission module. It is just an ordinary one without transmission. How to solve this problem? How did people achieve those electronic watches, electronic clocks, and perpetual calendars in the past? There is no calibration and no networking.

dcexpert

QWE4562009 Published on 2021-7-3 18:05 The key is that there is no wireless transmission module. It is just an ordinary one without transmission. How to solve this problem? In the past, those electronic...

Electronic watches are manually calibrated

Jacktang

Since it cannot be calibrated online, there is no wireless network control function.

In addition to manual operation, how can I make it adjust the calibration intelligently?

Is it by intention?

suoma

What should I do if the button battery is dead and the clock does not update automatically? - Microcontroller - Electronic Engineering World - Forum https://bbs.eeworld.com.cn/thread-522249-1-1.html

wsmysyn

It's the same as an ordinary electronic perpetual calendar. You just need to calibrate it manually regularly. There is no other way.

No matter how high the crystal precision is, there will still be errors. For example, if the crystal is 10ppm, there will be an error of 1 minute in more than 2 months. It depends on whether you can accept this error.

Do you really need such high-precision time measurement? If it is not important, just leave a setting that can be adjusted manually.

32.768k is more commonly used. There are also 32k RTCs. It depends on what the chip manufacturers think.

LuJianchang

Using a real-time clock chip

QWE4562009

dcexpert posted on 2021-7-3 19:07 Electronic watches are manually calibrated

How to calibrate manually? Can I send commands directly through the serial port? Or do I need to use a host computer?

QWE4562009

wsmysyn posted on 2021-7-4 10:47 It is the same as an ordinary electronic perpetual calendar. You just need to calibrate it manually regularly. There is no other way. No matter how high the precision of the crystal is...

For example, if the value is 10ppm, there will be a 1 minute error in more than 2 months. How is this calculated?

wsmysyn

QWE4562009 posted on 2021-7-5 15:36 For example, if it is 10ppm, there will be a 1 minute error in more than 2 months. How is this calculated?

It's just a math problem. The crystal accuracy is 10ppm.

This means that the error in 1 million seconds is 10 seconds.

1 million minutes error 10 minutes,,

100,000 minutes has an error of 1 minute. It is obvious how long 100,000 minutes is.

QWE4562009

wsmysyn posted on 2021-7-5 15:43 It is just a math problem. The accuracy of the crystal is 10ppm, which means that the error of 1 million seconds is 10 seconds, the error of 1 million minutes is 10 minutes, and the error of 100,000 minutes is...

---There is another question. If the network can be connected, there is also the problem of baud rate error. That is, the baud rate sent by the GPS module to the MCU (because the final LCD display is displayed by the MCU). If the baud rate is 115200 and the actual value is 11500, can the error of one day be calculated? There is also an error.

wsmysyn

QWE4562009 posted on 2021-7-5 16:20 --- There is another question. If it can be connected to the Internet, there is also a problem of baud rate error. That is, the GPS module sends to the MC...

This can be estimated. Even if the baud rate is accurate, there will be errors. When you send data, it takes a certain amount of time to receive, parse, and update data. For example, the data sent occupies 14 bytes (year, month, day, hour, minute, and second. The actual time may be longer than this, such as defining the data frame header, frame tail, and checksum). 14 bytes are a total of 112 bits. It takes about 1ms for the serial port to send 112 bits. That is, if you write the sent time directly, it is actually 1ms later than the standard time. However, this 1ms is fixed. If you know this error, you can compensate for it when writing to offset this fixed error. The main source of error is the cumulative error of the crystal. The more accurate the crystal, the more precise the time, and the longer the interval required for calibration. Conversely, the worse the crystal accuracy, the shorter the interval required for calibration.

When I was a kid, I had an electronic watch, the kind with a 32k crystal attached to the RTC, the error was very large, the accuracy was probably only a few hundred ppm, it could be a few minutes faster in a day or two, and it could be a day or two faster every few months, and I often had to adjust the time manually.

dcexpert

QWE4562009 posted on 2021-7-5 15:35 How to calibrate manually? Can I send commands directly through the serial port? Or do I need to build a host computer

A long time ago, people used television or radio to tell the time and set the time using electronic watches.

If the serial port can send commands, the computer time can be synchronized.

QWE4562009

wsmysyn posted on 2021-7-5 16:45 QWE4562009 posted on 2021-7-5 16:20 --- Another question. If it can be connected to the Internet, there is also a baud rate error...

You said a lot, thank you, but I still don't know how to calculate the error. For example, the baud rate is 115200, but it is actually 11500 or 11000. In this case, can the error of one day be calculated?

QWE4562009

dcexpert posted on 2021-7-5 17:25 A long time ago, people used television or radio to tell the time on time and set the time on electronic watches. If the serial port can send commands, ...

When sending commands through the serial port, it is also necessary to prepare the protocol in the target board program first, right? "

dcexpert

QWE4562009 posted on 2021-7-5 18:29 When sending commands through the serial port, it is also necessary to prepare the protocol in the target board program first, right? ""

That's natural. There is no standard protocol for serial communication. You can set it according to the situation. If it is a network method, it is calibrated using NTP.

QWE4562009

If it can connect to the Internet, there is also the problem of baud rate error, which is the baud rate that the GPS module sends to the MCU (because the final LCD display is displayed by the MCU). If the baud rate is 115200 and it is actually 115000, can the error of one day be calculated? There is also an error. This is a practical problem encountered by a software engineer I work with. Because the MCU cannot run at such a high frequency, only a 4M crystal oscillator can be used, and then 115200 is required to communicate with the wireless module. Then, after calculation by the FAE of the original microcontroller factory, the required crystal oscillator is 7.0 MHZ, which also has this frequency. As a result, there is a deviation when it is put up, because the MCU does not support this crystal oscillator frequency, but there is no other way. It is impossible to change the chip because it involves algorithms and the chip replacement cycle is too long, so the error occurs... Can this error be calculated? Regarding the baud rate deviation that causes communication errors between the MCU and the wireless module, and then there is also an error in time.

kiverin

QWE4562009 Published on 2021-7-7 11:53 If you can connect to the Internet, there is also a baud rate error problem, which is the baud rate sent by the GPS module to the MCU (because the final LCD display is displayed by the MCU) such as...

The module baud rate is fixed at 115200? In this case, the 4M crystal oscillator is indeed difficult. In addition, why does the baud rate error affect the timing? Isn't the module used to send the standard time to the MCU (for example, the module informs the MCU at 12:00:00 every day, and the MCU can adjust the time according to this time)? There is no need to use the module for real-time correction, the accuracy of the RTC within a day should still be within the allowable range.