Hello,

Perhaps this page might give you an idea:
https://www.circuitvalley.com/2012/02/pic16f917pic16f1907-7segmentlcddriverex.html

Bertus

 

I dont think its having one. Or at least I didnt find one. As you can see Im driving it blindly.
This is the original page I bought them : https://www.aliexpress.com/item/1005005362685005.html
If you search for similar models, you will get across that internal wiring and table I colored and showed earlier. Not present on my page though. Here is the full complete name of my device. This is 3digit. There are 2digit ones as well, and I think they are all very cute.
But very hard to 'manual' drive them as Im trying. Hard, until I will figure out a way.
View attachment 300851

It's clearly a 3V, 4 backplane, multiplexed LCD. It will work with the proper driver at 3V.

7 or 9V DC or square wave (which is 14 or 18V when driven with your XOR gates) will likely damage it.

 

I took a 2days break and I decided I will NOT continue this project as it is now. With the logic ICs. It demands higher voltage and I dont want to risk the IC's that are involved. The LCD I dont care that much but the ICs I have them in limited number. I also dont know how to add that higher voltage to the cct because it must come from the clock itself passing through some buffers. And that might potentially damage the buffers.
Also, another important reason is the fact that these LCDs are working already at 5V or even 3V ! So if there are already other solutions for less voltage driving, I will wait until I will find those solutions and understand them better. This is a first trial I did here anyway. Some ideas I got them wrong, and no one can see it.
The 3d reason; the HT1621B driving chips will come soon enough. They should be the answer to drive these multiplexed troublesome LCDs.
----
I plan, while waiting for the chips, to drive the 'easiest' 4digit LCD. This should be no problem, right? I wonder how it will behave at fast speed. This is the current problem I have right now with the 3digits, speeding up the segment location to create a number, is diminishing the segment contrast to 0%, not even gray. The higher the speed, the lower the contrast.Thats how I deduced it needs higher voltage. So I kind of expect this to happen from the new 4digit LCD. The history to repeat. If not, and everything will work fine, then that will be awesome. But I dont raise my expectations for now. Im kind of beat up at this point.

 

...these multiplexed troublesome LCDs.

There is nothing troublesome about multiplexed LCDs. Your "logic" solution is troublesome.

The higher the speed, the lower the contrast.

Drive it properly and you will have the stability and contrast the manufacturer intended at the design voltage.

Im kind of beat up at this point.

Entirely self-inflicted.

 

Hahaha

 

Take a look here at the circuit diagram and "control" description:
https://github.com/tardate/LittleArduinoProjects/tree/master/Electronics101/Displays/Lcd3Digit

 

I have used this LCD driver ICL7211A.

Edit: This should read ICM7211A.

 

Take a look here at the circuit diagram and "control" description:
https://github.com/tardate/LittleArduinoProjects/tree/master/Electronics101/Displays/Lcd3Digit

I know about it already. It didnt helped me.

I have used this LCD driver ICL7211A.

You mean ICM7211A - I looked onto the datasheet and it is interesting alternative.
I made a mistake buying a ICL7106 thinking is a 3 digit multiplexed driver. But instead it is a voltmeter chip WITH LCD driver incorporated. Well... I will use it someday.
I already buy a CD4543 and I hope I made a right decision. Meaning, that I can drive an LCD both through Logic gates OR with a PIC/Arduino. It should be possible with all, but I will have to actually put my hands and try them all to be sure. I will receive DIP and SMD versions of this chip because DIP for testing and SMD for implementing.
I just look more closely (NOW!!!) -hahaha- on my CD4543 datasheet, and it doesnt specify it is for static display. But reading 2 times the short introduction text it results that it is for a static as long as I am putting a square wave pin6 named PHASE and also linked to the backplane of the LCD (or COM1). If permanently is to 0V or to 5V it will drive LED displays.

 

An important detail. Both my LCDs are 3V(not5V) . I just looked in my CD4543 and your ICM7211A and they have a minimum 3V operating voltage, for the chip itself. But nowhere is specified the output signal voltage. I assume, it will be the VCC, so 3V as Im powering the chip with. Im counting on it. We'll see.

 

ICM7211A are extremely expensive! My solution is cheaper.

 

My solution is cheaper

Your solution doesn't work? Am I missing something here? You have a multiplexed LCD and the 4543 will only drive static LCDs, as I always thought. How will you drive the com lines with the CD4543 in the way?

 

Your solution doesn't work? Am I missing something here? You have a multiplexed LCD and the 4543 will only drive static LCDs, as I always thought. How will you drive the com lines with the CD4543 in the way?

What? Why do you say I am driving a multiplexed LCD with the a 4543 IC? Haha. We already changed the subject. Pay attention.

 

ICM7211 US$4.50
ICM7211M US$5.00

 

SO, I have NO idea how these multiplexed LCD work.

Some days ago:....I have an idea.... I believe, all the segments must get a CLK signal, in the same time. All 7 segments of a single digit, or all 21 segments for all 3digits. Right? On every connection line. Now, if I want to activate a segment, I will switch the normal CLK signal into a NOT_CLK signal. While everything else is normally CLK-ed.
----
Said and done.
Today, I made this cct here (both in Sim and in Reality and both worked...but not really)

and what this does,
while C1 is 0, down buffer is activated, permitting the oscilator to feed on the C1 line of the LCD.
When C1 is 1, up buffer is activated, opening the inverted signal through the XOR get on the C1 line of the LCD.
So instead of floating C1(and C2) line of the LCD when are not used, I am oscilating them all the time. Just to keep them active and not floating. Thats the idea. And it worked in reality and in the sim !!!

The problem is, if I add some oscilation on the COM wires, either I get the correct segment displayed, and if Im inverting the signal, Im getting random segments litting up. If the COM wires are floating, everything is fine as until now.
But the big problem didnt got resolved with either cct. The segment gets dimmed out as the fv rises.
Damn. At least I tried my best.
---------------
From another perspective, I managed to make a static LCD driver only from Logic Gates + some friend corrections.
As you can see it is number 2 displayed in the img. This cct worked both in Sim and Reality.

I already made a Sim file with a 40110. to drive this 4digit static LCD, all its 4 digits actually. That's cool...
I only made it in Sim. It waits to be made in Reality. I actually put this project aside, and give priority to the multiplexed one. Damn... it didnt work.

 

SO, I have NO idea how these multiplexed LCD work.

This is (has been) obvious.

But I already provided you the waveforms required (long ago). You can't get there with digital logic only.

You need at least 4 distinct analog levels: 0, 1/3Vlcd, 2/3Vlcd and Vlcd for the coms and segments, and they must be driven in the correct sequence, depending on which segments are on and off.

You can do this with discrete logic and analog switches, but it's not simple.

Your best bet is to get a proper LCD driver IC, or an MCU with a built-in multiplexed LCD driver.

 

Vlcd

Vlcd = 3V

You need at least 4 distinct analog levels: 0, 1/3Vlcd, 2/3Vlcd and Vlcd for the coms and segments, and they must be driven in the correct sequence, depending on which segments are on and off.

I am integrating an Arduino for the moment. But I plan to use a PIC12F508 in the end. So the "correct sequence" will come from their code. So thats no problem at all. The biggest problem is that I dont fully understand the hardware for this -multiplexed- chip.
Can you make me a circuit diagram with these 4 Voltage levels that you mentioned, what it might look like? Just to put me on the right path. Because Im experimenting for 2weeks or more and the progress is very slow and I hit a lot of errors. I managed to overpass most of them. Now Im at the final monster error. If I can beat this... ohohoa... So, please take a try.
Thank you.

 

You need at least 4 distinct analog levels: 0, 1/3Vlcd, 2/3Vlcd and Vlcd for the coms and segments,

So, if its like you are saying, dependent of the voltage, so in my case Vlcd=3V so the 4 voltages are 0V,1V,2V,3V. Thats it.
So, if you are saying it is dependent of the voltage ONLY, then if im using some resistive votage dividers, wont work? Or, if it needs more current, although I know a LCD is operating with uA or even pA ! Thats why they last so long on a single button battery. But IF resistive voltage divider are too low current, then if Im using some voltage regulators and take the voltage from them, theoretically as you say, it will work? Im open to everything at this point.

 

Im open to everything at this point.

Then get a driver.

 

Then get a driver.

Hahaha, I got 10 of them, they are on the road. But I want to make a driver myself, from logic gates.

 

You need to get your head around the interaction of the voltages supplied to the backplanes and segments.

Making a driver for a multiple backplane display from logic chips is a challenge, but I think you could get there by using the logic to switch mosfets to supply the multiple voltages to the backplane and segment lines. Personally, I think it is akin to making a cpu out of discrete transistors, but I will be interested to follow your journey.