Sunday, 3 March 2019

Making a cheap 20x4 lcd fit a Prusa MK2-MK3 case

For a while my replica Prusa MK2 has been bugging me.

It works great, just like a real one, but...  the LCD is the wrong colour!
My LCD is a yellow colour and the real ones are blue.

So I searched online for a blue 20x4 LCD. Most suppliers would not promise a particular colour.  But I did find one that promised and supplied blue.

Although the general shape was what I needed, there where several issues that made it incompatible with the MK2 and MK3 LCD cover.

Firstly the contrast variable resistor.
Back of 20x4
The large blue and white variable resistor sets the contrast, but this particular version is to high. You cannot slide the mounts in place as they hit the top of the resistor.  This board is well designed though, it can also take a small surface mount variable resistor. (The three empty solder points to the left) 

new and old contrast resistors.
These are both 10k. I swapped the large for the small one. That solved this issue.

On the front are two more issues
Controls and buzzer.
The encoder is to tall and the button is to short

The replacements.
The replacement encoder is a "Rotary encoder,code switch/EC11/ audio digital potentiometer,with switch,5Pin, handle length 15mm" the switch is a "Momentary Tactile Switch DIP 6 x 6 x 7"

With these installed the Rotary knob sits at the correct height and the stop button can be activated. 

The switch is a little low a 6x6x7.5 might have been better, but I didn't have any, the 6x6x8 was to high. 
The selection I had... and still not the one I needed
You always need the one you don't have....