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Critique my first PCB

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carl0s:
So it turns out I had the LCD pinouts back to front :o

My first attempt at reflow soldering went well. Little bit too much paste - bridge on a pin that didn't matter.

but the LCD backlight driver didn't work. Progress was hampered by the fact that I've only ever done Arduino. Between Keil and TrueStudio, I had a hard time getting the discovery board example programs to compile. I needed them to compile so that I could add in an 'HAL_GPIOB pin1 enable' thingy.. i.e. turn on the LCD backlight, since the examples are all meant for the amoled screen with no backlight.

I did some playing. In fact I burned out one of my LCD flat flex by sticking a li-po on it and getting the polarity back to front. I guess this is why I need a current limiting power supply. DP711 or DP832 though.. ? DP832 is more money but crucially its kind of huge :(

Anyway then I constructed a better test.. 5 plain LEDs wired in series on some breadboard, to be driven by my little circuit. and it worked! 3.3v in, drives 5x LEDs nicely.

Then I looked closely at the LCD datasheet for the FFC pinouts and it looks like I had it the wrong way up. Well, what I mean is that I assumed the FPC to be going in the connector at top-contact rather than bottom contact. So pins 1-17 should be pins 17-1 instead. Left to right-flip.

I don't think this is fixable. So I have 49 keychain PCBs :)

In all honesty, it quickly became apparent that I have made myself a PCB here that's very difficult to debug (since it's face down when fitted to the ST Discovery board). Perhaps I'll spend a bit more time on rev 2 and put some test points, as well as maybe more than one type of LCD connector.

carl0s:
Checking over my designs and I can see why it's happened. I used Molex 504281-1700 in the design, which has contacts on both top and bottom. I have 5 of these connectors. I actually fitted a flip-connector though (Amp 10061122-171120HLF), which seemed to grip the FPC better, and was dirt cheap. These are bottom contact only. So it might be Ok after all if I use the other connector :)

CopperCone:
Did you protect your I/O? I did not look at it but there might be special things you need to do if that chip is the first thing in the circuit connected by a wire.

And how is that board being mounted mechanically? I don't see any screw holes. I assume it clips into a assembly some how? Keeping it stationary is important.

carl0s:
Hi. The Samtec DSI connector makes a tight fit!

I'm just reflowing a second attempt now. I had some 17-way 0.3mm top contact flip connectors.. unknown brand from Aliexpress. Just trying again with one of those ;)

I only have one more of these LCD panels left though :)

carl0s:
Sweet. It works!

There were a couple of solder bridges there which were on unused pins, but I've wicked them out now anyway.

Just need to figure out what needs changing in the LCD driver code now !

This is a marked improvement from a couple of hours ago where I thought I'd designed the pin outs back to front and would have to re-do the design!



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