LCD-Displays, series resistor, contrast setting


Hi all,
since some of you have had problems with their LCD-display, something good to know.

I have two new ones of LCD2004A. Both have integrated resistors for the backplane light. 
See the red circle on the photo LCD2004: there are 51ohms (signed "510" on it), will say you can use it with the 5ohms series resistor on the board without any harm to the display. The producers have learned to enhance their products.
The old one I use at my controller has no series resistor. So an additional one on the board was necessary.

The contrast is set with with a small voltage at pin3 of the display unit. On our boards there is a 10k potentiometer as voltage divider which gives the possibility to find the best contrast by turning it. The aerea is very small, so turn SLOWLY. The contrast changes from "all blocks" are shown to "blank plane". You must find your individual point. Contrast also is changed by temperature, not a lot , but it does.

Hope it helps
73, Immo, DL5KB


Good to know information!

This is all very good information and could be used to update the instructions but even so the help on this thread has been nothing but stellar!

I am thankful for the patience and help from you and the people on this message board!

Thank you for the information and thank you Johan and the other people that have responded!

OK, gotta go now, I have work to do and then later more work on my tuner!


If I had understood you correctly, it is R1 that can be reduced to 5 Ohm


R1 is 4.7 ohms according to the schematic. It is apparently suggested to use 10ohm but I think that is suggest if there are no other resistors in line....


hi patrick and Andrew,
the 5 ohms are only sufficient, if there is a BUILTIN SERIES RESISTOR on the display unit like shown on my photo. Think about that not all units have this resistor. You have to verify this first!
73, Immo, DL5KB


Thank you. My display lighted up and I can continue working on my project.