Fixed IO Peripheral PCB - IO from Scratch

Added: 2026-06-03

[00:00:00]Hello and welcome back. I'm hoping today's video is going to be quite straightforward. I've got the IO peripheral board and that provides SPI interfacing to a number of embedded devices and some headers for external connections. But when I turn the breadboards into a PCB, I made a mistake and I've got some pretty ugly bodgege wires on there. And today I'd like to get that resolved and get a nice better looking build. Let's take a quick look at it. So this is the IO peripheral board and you can see the nasty BGE wires here. Now those are the only BGE wires that still exist in the build. Now I do have this Bodgege PCB underneath pipeline stage two, but I'll need to do a whole new back plane to resolve that.

[00:00:41]And I expect that will probably be the last PCB I do in this build. The most used thing we use this board for is just the SD card interface.

[00:00:50]That allows me to have a basic operating system that I can interface with the system with.

[00:00:56]But I do have some GPIO pins that I use the MCP23 SO8 chip for do have LEDs outputting to show their current state. Got the real-time clock and the RTC gives us time and date functionality. The date is correct, but the time has drifted by a few minutes and I suspect that might be because these capacitors are not the correct value. I had planned to replace those soon after, but because I knew I was refreshing the PCB, I've not done so.

[00:01:40]The time is actually pretty good because it's been running for a very long time without uh drifting that much. It actually keeps better time than a cheap wall clock I've got in my bathroom. But I have the correct passives to replace those with now. But these wires do look quite fragile, and while they've held up for a decent length of time, I do worry every time I uh go anywhere near them.

[00:02:01]So, let's get that sorted.

[00:02:03]First up, we need to fix the issue on the schematic and then get a PCB ordered.

[00:02:12]Let's fix this.

[00:02:54]Actually think it' be better to remove that circle.

[00:03:12]Let's make that a little bit clearer.

[00:03:16]That should be fine now. What's it complaining about?

[00:03:31]That copper area wasn't rebuilding from this option.

[00:03:36]H it's a different selection. Oh well.

[00:03:42]This is why it's good we have DRC checking.

[00:04:22]Looks okay. Let's get some paste on there.

[00:04:36]This RTC package is the one that's most difficult.

[00:04:55]That pad in the corner of the SD card holder is only partially covered.

[00:05:03]We got some definite missing paste on those.

[00:05:12]That's better.

[00:05:33]So, I've had more difficulty with this pace than I normally have. Though, the results are looking quite good.

[00:05:43]I think my problems come from not cleaning the stencil quite well enough after the first PCB attempt.

[00:06:15]only two of these 10 microfarad caps and nine poparad is not a common size.

[00:06:22]It doesn't even exist in my uh my book kit of caps. So I bought 10 specially for this.

[00:06:39]This is the crystal that the RTC depends on.

[00:06:44]I think while we're here, we should do the RTC.

[00:06:53]And I've got the power regulator.

[00:06:57]And now his little fats.

[00:07:17]We use these for the voltage level conversion between 5 volts and the 3.3 that the SD cards need.

[00:08:02]Okay, I'm slightly worried about the amount of solder on that pad up there.

[00:08:10]Let's watch that one carefully.

[00:08:29]In the old version of the board, this is the chip we had to take off in order to do the budge wires.

[00:08:46]Some of these chips, the markings don't show up very well under this light, which is annoying because everything else about this light is great.

[00:09:00]So 138 de multiplexer.

[00:09:11]I'm pretty sure this is the most fiddly PCB in the entire build today.

[00:09:17]So I didn't relish the fact that I made a mistake on this one and would need to do it again.

[00:09:52]Right. I think that's everything. So time to reflow.

[00:10:21]Let's take a look.

[00:10:29]Was a bit worried about these guys, but they look okay.

[00:10:40]Okay, I'm a little bit worried about that pin.

[00:10:48]That one actually looks a little bit sus to me.

[00:10:51]I know from experience though to uh test it rather than just start poking it with a soldering iron.

[00:11:09]Okay, that crystal's got a bit of a tilt on it as well.

[00:11:57]It's lifting very slightly.

[00:12:28]Okay, nothing left to do but give it a test.

[00:12:33]Now we find out if it is going to be a simple video or not.

[00:12:48]See, we need the CR2032 battery.

[00:12:53]It will work without this, but that obviously allows it to keep time with the power disconnected.

[00:13:06]Now, moment of truth.

[00:13:12]And that is not a good sign.

[00:13:29]All right. So, it's not able to read from the SD card.

[00:13:48]Let's start off looking at the essential bits of circuit.

[00:13:55]There was a pin up here I wasn't too sure about, but that kind of looks all right from a different perspective.

[00:14:08]Doesn't look right there, does it?

[00:14:38]Now, that pin does look dodgy to me.

[00:14:45]Let's give that a try.

[00:15:11]Okay, I do see the tiniest of solder bridges there.

[00:15:28]Ah, okay. So, one or more of those solder joints was the problem. This is excellent. So, we've got the SD card prompt. That tells me that the boot loader has successfully loaded the operating system from the SD card. So, this circuit is majority working. Just need to test the other bits.

[00:15:53]Okay, so the RTC obviously doesn't have the correct date and time in it, but that looks like power on details. So, this does give away that I spent just over 6 minutes tracking down those dodgy solder connections and getting this working.

[00:16:11]Right, that's the correct date.

[00:16:14]Now, I give away how long it's taken me to do all of this.

[00:16:30]Now, I will come back to this at some other point and get an idea for how well the clock is keeping time, but with the correct capacitor values this time, I'm hoping it will do slightly better than the old board, but that did quite well.

[00:16:44]So, it's just the GPIO we haven't tested now.

[00:16:50]direction zero means output.

[00:16:55]Let's try turning all the bits on which should appear here. Perfect. So, not only is the GPIO chip working, but all the LEDs are wired up correctly.

[00:17:11]Excellent. That looks like we've got a fully working IO peripheral board. Very pleased with that.

[00:17:17]Okay, I was worried there for a sec, but I'm very pleased we got it working. We didn't have any errors on the PCB. We just had a couple of solder blobs that didn't quite reflow perfectly. And I'm thinking the stencil was probably at fault there or it might just have been a bad luck. But it is a big reminder that you need to clean stencils after use cuz the solder paste after it's dried on is a real problem later on. So, you'll thank yourself in the future. Well, I hope everyone enjoyed that. As always, a big thanks to my patrons and supporters.

[00:17:46]I really do appreciate it. And now we've got rid of all the bodgege wires. I'll be moving on to adding some additional circuitry to the build. See you again soon. Goodbye.

[00:18:41]>> [snorts]