Optrex LCD on STM32F4 core

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Hi there,

as the title implies i ask myself if there is anything to consider using these LCDs

http://www.mouser.de/Search/ProductDetail.aspx?R=C-51850NFQJ-LW-AANvirtualkey51610000virtualkey805-51850NFQJLWAAN

with the new STM32F4 core.

 

Cheers and thanks

[CJ55]

I use this display on my MB SEQ V4 with the STM32F4 Core and on other stuff. You have to consider that the backlight must not connected to 5V directly. It needs an additional resistor (25 Ohm) between pin 15 of the display and the Core. Otherwise it get destroyed (own experience)! See point 2.4.2 of the datasheet.

[=FFW=>]

oh - alright. thank you so much! where did you put the resistor? directly within the connecting cable?

[CJ55]

[=FFW=>]

hey cj55,

thank you very much for the effort to make it clear with these pictures.

great build. great wiring. respect!

i have attached the resistor the same way you did it.

have you read about the altitudes way of connecting the optrex displays?

he was using the green on black optrex displays with his way of improving the contrast of the displays.

i soldered a 30 ohm resistor in there and ask myself if the resistor in there relates to brightness or to contrast -

because i feel that the contrast should be a bit better.

so what do you recommend? is this resistor related to contrast? would a 25 ohm resistor improve contrast, or not?

why excactly have you chosen this value?

cheers and thanks!

[CJ55]

No, the resistor is only there to protect the backlight LEDs of the display for to much voltage. The max. voltage for the backlight LEDs is 4V (or typ. 3.5V). The advantage of this resistor is, you don't need to change anything on the MB_CORE_STM32F4. But you can still use both trimmers on it without the danger of giving the display to much voltage. One trimmer is for contrast, the other for backlight brightness.

How to calculate the resistor: you have the current of the backlight LEDs: 60mA (datasheet). The same current flows through the resistor (series circuit). The voltage at the resistor is 5V - 3.5V (datasheet) = 1.5V. Then Ohm's Law: R = U/I = 1.5V / 0.060A = 25 Ohm

If you can not get a good contrast/brightness ratio with both trimmers, then you can try Altitudes way and remove transistor T1, resistors R12, R13 and trimmer P. And connect an other (better) trimmer directly between pin B- of J15 and ground. But you have always to make shure, you have the 25 Ohm resistor in there. Either here in series with the trimmer or in the cable.

Most displays have this resistor built in, so you can connect the backlight directly to 5V, but unfortunatly not all.

Edited October 29, 2015 by CJ55

[=FFW=>]

this is a very elaborated and understandable answer. thank you.

now i think i will accept the way it looks for now. at least, its readable

it looks quite similar to yours around the outer right part of the right display in your picture.