Understanding of a digital tube drive circuit (Part 2)

辛昕

Understanding of a digital tube drive circuit (Part 2) [Copy link]

 

The final conclusion should of course be posted in the main post!

I shot another video and added a shell to cover it. This is usually how actual products are usually made, so the overall display will look much better.

带壳

循环计数

This is a circuit based on STM32G030F6P6. It is really simple. Although the picture is not very clear, you should be able to see it.

This is a minimal system, it has nothing.

In addition, the digital tube circuit is just a few resistors, no transistors, and no driver IC.

This is actually a very simple question and is not worth mentioning at all.

It’s just that the Purun microcontroller is rubbish.

Although it is really cheap, just a few cents, it may not be usable.

Many years ago, I wrote a post like this:

You can tell from the time that it really has a long history.

Recently, I was sorting out a problem about the digital tube driving circuit again - but this time, I was a little more successful - I was thinking about how to reduce the external driving circuit as much as possible and use the MCU's IO port for direct driving.

I briefly reviewed this post - the so-called "previous post" without writing the "previous post". To be honest, my face turned red -

Not only was my foundation in software and hardware really poor back then.

In addition, when I am discussing an issue, my ability to lead myself astray is really amazing .

Of course, I have corrected this bad habit.

Now, I can simply summarize this matter in two sentences:

1. In order to make the brightness of each segment of the digital tube uniform when displaying different characters, of course, current limiting resistors must be added to each segment.

This has nothing to do with common anode or common cathode;

This is the core point I wanted to express when I was complaining about that circuit - of course, it is also very simple.

辛昕

As for the second sentence, it is about the base resistance of the transistor and the current limiting resistor on CE.

Regarding this issue, I am not particularly concerned about it for now.

But obviously, in the many years since then, I have actually been making a mistake. Since I have been using switching circuits built with triodes most of the time - that is, my base current is in saturation most of the time, I naturally don't need to consider the current limiting on the base at all.

However, once I really started to think about making the triode work in a linear amplification state, this issue had to be considered.

Of course, back to this question - in the driving circuit of the digital tube, if you want to use a triode to drive it -

My conclusion is actually...

It's just a switching circuit. Just saturate the base. Why are you still thinking about the bicycle?

——So, let’s not discuss this issue here.

(I just woke up, haven’t eaten yet, haven’t changed into pajamas yet, I hope I didn’t make any mistakes, God bless me, God bless me)

辛昕

The next problem is a small problem in the main building that will not attract attention.

That is, common cathode or common anode?

This, indeed...is not a problem.

Because, if you want to minimize the peripheral circuits of the single-chip microcomputer to control the digital tube, then——

You just need to start from the fact that the source current is usually less than the sink current, and it is almost inevitable that you will choose common cathode.

Of course, there is also a small problem here - for so many years, I have never really cared to distinguish, pull current? Sink current? Is it going into the microcontroller or out of the microcontroller?

So, I habitually turned on AI - using AI for searching is quite efficient.

And it’s really great that domestic AI doesn’t need to go over the firewall.

Moreover, this time, I am very satisfied with Tiangong AI's answer——

I mean, normally, I'm not very satisfied with these kinds of AI answers.

Yes, you need to understand the source and sink current, the core is -

Where do you want to place the microcontroller?

It is the pull (MCU) current and the sink (MCU) current. As long as you think about it,

It's easy for you to remember, oh——

Pull means that the output of the microcontroller IO port is high and the current is pulled out from the microcontroller by the periphery.

Filling means that the output of the microcontroller IO port is low, and the current is poured into the ground through the microcontroller IO port by the periphery.

辛昕

An ideal single-chip microcomputer direct-drive digital tube circuit (currently imagined)

Whether this circuit is reasonable and feasible, there are only two things to consider:

1. What is the designed current for each section? Is the pull current of the microcontroller sufficient?

2. Calculate the maximum current when all 8 segments are lit to see if it meets the current requirement of the microcontroller.

Of course, on different devices, there are requirements for the source current and sink current themselves.

Usually, there are actually some combined restriction issues.

For example, the total source current cannot exceed a value.

For example, the total current flowing through the entire microcontroller cannot exceed a certain value.

Of course, one point that must be made here is:

Because I must use dynamic driving, that is to say - at any moment, no matter how many digital tubes there are, at any moment, I actually only light up one bit.

Therefore, no matter it is sourcing current or sinking current, every instant is just a value on a digital tube.

Of course, I actually have a little bit of worry in my heart——

If it becomes dynamic, will there be any impact?

仙猫

This is going to be pursued to the extreme, what a twisted logic!

Still so cocky.

辛昕

Xianmao posted on 2024-4-4 12:26 This is the ultimate pursuit, what a twisted dog! And he is still so cocky.

Wow, you actually showed up! You're awesome! You're still alive!

Bullshit, I want to save money on components, but the PCBA area is too small

辛昕

Xianmao posted on 2024-4-4 12:26 This is the ultimate pursuit, what a twisted dog! And he is still so cocky.

What’s your WeChat?

xujian2000

Hello! Long time no see!

仙猫

Xin Xin posted on 2024-4-4 12:55 Wow, you actually showed up! You are so thick! It turns out you are still alive! Bullshit is the ultimate pursuit, I want to save money on components, but the PCBA area is too big...

These days, some constant current driver chips that connect to serial ports are quite useful and do not require too many pins. However, if you still want to save a few cents and chase the poor enemy, of course, it is also a good habit of hard work and simplicity.

仙猫

Xin Xin posted on 2024-4-4 12:56 Where is your WeChat?

Is it the Q account from back then?
I created this account when mobile phones were not popular. Later, I had to register my mobile phone with my real name, but I ignored it. So I was sentenced to death and disappeared physically.

辛昕

Xianmao posted on 2024-4-5 13:06 Is it the Q from back then? I created an account in the days before mobile phones became popular. Later, I had to register my mobile phone with my real name, but I ignored it, so I was sentenced to death and disappeared physically. ...

I have been calling your QQ affectionately for a long time.

You've really been dead on the Internet for a long time.

辛昕

Xianmao published on 2024-4-5 13:05 These days, some constant current driver chips that connect to serial ports are quite useful and do not require too many pins. However, if you still want to save a few cents and chase the poor enemy, of course, it is also hard work...

Fuck, why is it always gray~~

No, it has been confirmed.

In the final analysis, it's just that Puran's rubbish MCU is not good enough

I used STM32F103C8T6 and STM32G030.

Damn it, suddenly the MCU is unable to be recognized by JLINK, damn~

Otherwise just take a photo and upload it.

It happened to be the Qingming holiday.

I have already sent an email to Puran, and he had another small temper tantrum and threatened them.

I can guarantee it, as long as it dares not to reply.

I will definitely publicize it loudly on Zhihu, 21ic, Weibo, and Bilibili, Pu Ran is a fucking garbage~~

辛昕

My CPU burned out.

The truth is that it is indeed a code problem, of course, an SDK problem.

Without further ado, here are the pictures.

Really, I lost.

仙猫

Xin Xin posted on 2024-4-5 21:42 I have been calling your QQ affectionately for a long time. You have really been dead on the Internet for a long time.

That’s right, I’m dead and there’s no way I can save myself, so I don’t want to live anymore.

To save a Q account by yourself, you need to find ≧2 contacts for proof, but those are basically business relationships with no other means of contact.

Several forum accounts also died due to lack of mobile phones. In short, one day you woke up to find that you had been strangled to death without any explanation.

辛昕

Xianmao posted on 2024-4-10 16:10 That's right, dead and can't be saved, and don't want to live anymore. Q account needs to find ≧2 contact proof to save itself, but there is basically no other way to contact them...

I said why I called you so passionately for several years but you didn't respond