Can the KL46Z drive a 7 Segment Display?

[neilporven]

Hi everyone,

I am trying to find out if the FRDM-KL46Z board drive a four digit 7 Segment display (not the glass one), but

the ones that are regular (not sure what to call them).

Thanks.

[TICS_Fiona]

Hello Neil

KL46Z has 64 LCD pins, it has no problem to drive four digit 7 Segment display.

The section 44.6.1 in Reference Manual contains an example for LCD 7 segment. 

https://cache.nxp.com/files/microcontrollers/doc/ref_manual/KL46P121M48SF4RM.pdf  

Could you please give more details of regular LCD?

Best Regards

Fiona Kuang

Technical Information & Commercial Support

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[neilporven]

Hi Fiona,

This is what I refer to as a normal 7-segment LCD

This is what I refer to as a glass 7-segment LCD

In the KL46P, it talks about supporting front planes and back planes, which is what the FRDM-KL46Z evaluation board has. 

I am wondering if the same pins on the KL46 that drive the LCD on the evaluation board, is capable of driving what I call the

normal 7-segment LCD.  The normal LCD is brighter, thus I imagine higher current drive and therefore I believe would require

either a logic current driver chip or some transistors as an alternate?  I don't believe going straight from the processors pin to

the normal LCD could be possible. 

Thank you,

Neil Porven

[dave408]

Hi neilporven​, I stumbled across your post and was interested in this LCD question.  Are you trying to leverage some sort of library that might be available for driving the LCD?  If you are basically going to be controlling the pins yourself, then the KL46P datasheet shows that the pins used for the LCD are also GPIOs, so if you configure them for ALT2 you should be able to use them to drive the LEDs.

http://www.mouser.com/ds/2/302/KL46P121M48SF4-783099.pdf

It looks like the KL46P can source 25mA max per pin, but I believe this is the limiting factor:

So if you need more than 3mA per segment, you'll probably have to go with an external driver.

[neilporven]

Thank you Dave,

I don't know if you seen the KL46Z evaluation board, but the LCD is so small and hard to see.  I had

used some module that drives that LCD and everything is working well, so I wanted to see if I can get

away with using what I call a normal 7-segment LCD to make my project more readable.  But apparently,

I am going to have to drive the normal LCD my self.

I am now searching to see if there are manufactures that make bigger glass LCD digits and (with/without backlight).

If you can recommend one let me know.

Thanks,

Neil

[dave408]

Sorry, I have never used one of those glass displays before.  Have you tried just hooking up normal 7 segment LED display to see if it still works?  3mA will be dim, but at least you'd know if you can get everything to work the same -- then you could hook up a few buffer chips to get the current drive you need, if you really like the normal displays.

[neilporven]

Thank you Dave,

No, I haven't tried just installing the 7-segment display to the MCU, but I believe it will not work.  The software module was build

for a display module that has front and back plane driving.  I haven't looked much on what it would take to drive a normal 7-segment

module, but I don't believe they work of the front and back planes as the glass module do.

I want to thank you for taking the time and trying to help me.

Neil