Two posts in a week, you lucky punters!
Screen/paint interface scenario
So, I finished printing the back of the screen, assembled it and it was all good. A few under-extrusion issues on the first layer but I figured the filler, primer and truck bed liner paint would hide my shame. This was not what happened, as the photo at the top can testify.
First of all, the filler was almost impossible to work with. Attempting to squeeze it from its tube was hell, especially with a wound on my finger (but that's a spoiler for later). I got a bit out but it didn't really fill much and didn't want to stay on the plastic.
Then the primer did... well actually the primer was ok. Did nothing to hide the layer lines and things but it went on fine. Did some light sanding either side of applying the primer. Layer lines will go when I get to the main course, right? Right?
Dear reader, my advice to you is this: never try and get an even coat of spray paint when it's windy. It'll go wrong. And then you'll absentmindedly go back across where you just missed and end up letting it get blotchy. Then you'll think, "I'd better try and blot some of this off before it becomes a disaster," probably a moment or two too late to avert the disaster that is now underway. You'll let it all dry overnight, then look at it and swear to yourself. "It's fine, another coat will deal with that." But it's still windy, and it doesn't make it better, nor worse, just differently bad. Finally you decide to live with the scars and slap laptop stickers over the most abysmal parts, vowing to do the painting over in the garage next time. Hashtag deal with it.
So anyway, the screen is assembled. Protective film has come off the display module and the PET sheet that protects it and I'm struck by two things:
- it doesn't look bad from the front at all;
- PET sheet is hella reflective and I might need to deal with that as well.
Your hand is not a vice
If you need to embiggen a 6mm hole in a bracket to allow for a ¼" bolt to fit through it (6.35mm), do not under any circumstances think to yourself, "Oh, that's less than half a millimetre, no problem at all - I'll just whizz this step drill bit around it to embiggen it, I can hold it while I do it."
Newsflash: at the first sign of resistance, the situation will see the hardware take the path of least resistance, and your fingers are less resistive than a steel bracket. I now have a gash along my left middle finger the same size as the width of said bracket.
With that being said, I managed to clean the hole up enough for the ¼" bolt, and the bracket looks like it will do a sterling job holding the screen to the main body.
It's not all about manky paint and bloody fingers though. I decided to take a close look at the chip nearest the speaker header on the display driver board (using my phone, because the camera is insanely good). The text was too small for my old eyes to focus on, so this was a very handy way to do it, as it turns out!
The traces going to the speaker header are also easy to follow, going through the 0Ω resistors to the chip. Now, I'm familiar with PAM ICs, they're the driving force of some really cheap-but-good amplifier modules. I've used these PAM8403 modules in a few things because they cost pennies (literally - I think I got them for 80p each) and go loud enough without distorting:
So, with the chip being known I also knew where to get the datasheet and what to look for, and I found the pins that the audio signal comes in on and where it's routed. Getting to the audio from the driver IC is a no-no, it's far too tiny to pull off, but I think I can tap into the pads feeding the PAM8003 so that I can mix in other audio sources, like the ZX Uno and a better audio output from the Pi, but still work for the external HDMI.
Confused? Yeah, it's a lot of messing about with words to say that I might not need the little amp kit I ordered (which actually has the PAM8403 chip on it).
It's a bank holiday weekend. I'll probably mow the lawn if my finger stops oozing for a bit. Until next time!