How-to: Change the color of your PCD8544 backlight, and make it look less ugly.

Part 1: Swapping LEDs on PCD8544 backlight
Part 2: Making PCD8544 displays look less cheap and ugly.

Part 1:

So i ordered a white-backlit PCD8544... and the bastids sent me another blue one!

Whatever, I can fix that. And blue is a boring color anyway. How about hot pink? Azzy, you don't have any hot pink LEDs Or maybe yellow, I have some of those in stock.

You will need:

PCD8544 module with PCB

4 surface mount LEDs. I used 1206 ones, but I had to chew away some of the plastic frame to make it fit. They used 805's, and those would fit much better.

Tools: Soldering iron with fine tip, diagonal cutters, tweezers (if you have soldering tweezers, the whole thing is much easier! Sadly, I don't)

1. The LCD and backing PCB are held together by those 4 metal clips. Pry them outwards gently, and you should be able to separate the PCB and LCD as shown below. A real gutless wonder - all the magic is apparently in the LCD.
   
   

If you look at how it fits together, it also becomes obvious why the screen leaks so much light to the side, and why you need to frame the visible area in black tape/paint/etc to get these screens to look decent with the backlight on. The LEDs are just sitting there on the sides, with one side practically exposed. We'll come back to that in the second section.

Steps 2-6 assume you don't have soldering tweezers. If you do, just desolder the old leds and solder on the new ones.

1. Remove the 4 existing LEDs. I had no success desoldering them, but wound up destructively removing most of the diode with the diagonal cutters (so the two sides could be unsoldered separately).

2. Remove as much solder from the pads as possible.

3. Holding the new LEDs in tweezers by the top of the light emitting part, position it as close to flush with the board as possible, being sure to check polarity (they are usually marked somehow, often with a dot of paint on one side). Do not position the LED farther from the edge than the old one. Solder one end.

4. Solder the other end - you'll notice that the LED is probably not sitting flat now. Applying pressure to the top with one leg of the tweezers, alternately touch each end with the soldering iron (the goal here is to get the solder under both ends melted at the same time long enough to get it flush.

5. Repeat process with all LEDs.

6. • test that the LEDs work.
     
     

7. Now - test fit the cover back on. You will likely find that it doesn't quite fit around the new LEDs, so you'll need to take the screen assembly apart and trim it. Carefully pop off the metal frame of the cover, and gently separate the plastic part from the screen itself.

8. Position the plastic part on the back of the PCB, and note where it is bumping into the LEDs. Carefully razor off little bits of plastic until it fits.

9. Carefully reassemble the screen assembly (metal frame, screen, plastic part) - it should now fit.

10. Snap it together, and verify that the screen works!

11. Now - you may find the brightness of the backlight to be insufficient, particularly running at 3.3v (or you may find it excessive). You can fix this by changing the value of the resistor, nominally 150 ohms.
    Connect the GND pin to GND. Then clip +3.3v (or whatever you're using) to a resistor either smaller or larger than 150 ohms (to make it brighter or dimmer, respectively), and touch the end to the side of that resistor at the top of the display facing the diodes (in the case of this board, the right hand side). Try different resistor values until you find the one you like, and solder it in place (this may be tricky if you don't have a stock of SMD resistors)

I wound up using 82 ohms to get my yellow LEDs as bright as the blue ones were.

Part 2

The PCD8544 is the go-to display for many of us playing with *duinos, largely on account of it being the cheapest display with high enough resolution to display much of a UI on. Unfortunately, it looks pretty lousy. This is how I made mine look a little nicer - note that the screen can't be easily taken apart after this, due to the glue.

One of the most annoying things is how the glow from the backlight leaks out the sides, and on the screen, is brightest on the sides, just beyond the pixels.

1. Carefully cut two strips of opaque, thin, somewhat stiff material just over 1/8th inch wide, and 1 1/4 inch long. I used the metal strips from those white acousto-magnetic anti-theft tags.

2. Glue the strips onto the sides, with the bottom flush against the circuit board, with cyanoacrylate adhesive (super-glue, crazy-glue, etc) - this will help block light leakage from the sides.

3. Using a fine paintbrush, apply black acrylic paint to the metal frame around the screen, as well as the outer 1/4th inch of the screen itself (don't worry about going too far in). If there are any gaps between the strips you glued onto the edges, and the frame, this is your chance to fill them with paint. Make sure the paint is thick enough that no light leaks through.

4. Connect the LCD to espruino, turn on the backlight, and drawRect(0,0,83,47) (ie, a rectangle along the edge of the displayable area of the screen.

5. Using a stiff, hard, non-metallic object, scrape away paint so the entire display area is visible, but nothing outside it is. The top layer of the screen is plastic, so you can't scrape hard.

6. Ta-da!

I daresay that looks sexier than stock - though I think I should have gone with red backlighting.

Nice! I think yellow looks better than red... It might be nice inverted as well so it was yellow text on a black background.

If you could wire the other side of the LED to another pin instead of ground, you could use red/green LEDs and could change the shade with PWM :)

For the masking off, what about black electrical tape? It might be easier to get nice straight lines around the edge, and a bit quicker than using paint.

Oh, yeah, inverting the color would look slick... If I back-lit with green instead, I could get the classic green-on-black look, which never goes out of style.

I wish there were space for more LEDs in there to get different colors.

Hmm - I'll have to try BET for that. I had gorilla tape cut into strips, and it didn't hold on as well as you'd expect gorilla tape to - and it looked awful. BET would probably look alot better, and might be easier than the paint. Making the seams look good would require care.