 The great search bar to buy did you key a native root every single week lady to use deserve powers of engineering for good and helps You find things on digikey.com. What are you searching for this week at digikey? Okay, so let's go to the overhead and I'll show you this board design. I'm working on so this is a KB 2040 so I designed this board. I think I showed off a couple weeks ago I'll finally have the PCBs in so it's a USB C RP 2040 boards is the RP 2040 and here's some like power regulator stuff and it's got cast-slated pins And it's designed to be pro micro shape, which means that it can be used in keyboards It's like it's specifically designed for use with keyboards That you would have plug USB C in and then it would generate the key commands while having you know LEDs or key matrix Annas and cathodes connected to this row of pins here so the RP 2040 we've chatted about and getting all the Added peripherals that you need the the Q-Spy memory and the crystal and I got some tactile buttons but one thing that was new on this board that I don't put on a lot of boards recently is a PTC fuse so the pro micro has a resettable fuse on it and Folks might be familiar with them because Arduino uses PTC fuses a lot, which is good because it helps protect the board in the computer now your USB Hub and computer has PTC fuses inside of it So if you ever plug in something to USB and actually Overdraws the current it'll shut off and you know you might have to like wait a couple minutes You might have to reboot the computer to get that port to come back A PTC fuse is a thermally. It's a basically it's a resistor. That's very temperature dependent So as more current goes through it it heats up And the resistance like goes way way high like so high that basically opens up and that basically the fuse is open Cutting off power until this cools down. So it's kind of nice because unlike a glass or you know wire fuse You don't have to worry about replacing it Automatically, you know self-heals you can get these in different currents and voltages and of course they're pick-and-place friendly. It's a very slim PTC fuse here. So we want one. This one is it's a pretty chunky looks like it's a you know, maybe an 18 by 12 1812 sized PTC fuse. We want one. That's much smaller. We're gonna have one. That's about this big It's 0806. We just don't have as much space on this board because you know, I have to maintain the The physical size So this this part here, this is the PTC fuse. So it's an 0805 I was like can I fit it a 1206 and the answer is no, there was just really no space I was just completely jam-packed in there. So let's go to The layout first real fast and we'll take a look at that. This is it. So this is the PTC fuse if I Get info on it. It's just called fuse and it's 0805 sized. So let's go for an 0805 Imperial sized fuse and we'll see what the options are and specifically this one's going to be connected to USB So let's you know do something that's that's USB friendly Okay, so too much stuff open here Okay, so Let's go to do the key and Let's search for PTC so it's a positive temperature coefficient fuse buys Close fuse Okay, so there's actually a whole category which I've used multiple times before a PTC fuses. So go there Okay, so now we have to decide what we want as our options So the first thing is well, obviously, let's pick active and let's also pick in stock only and let's exclude marketplace So we're only looking at stuff that shipping directly from did you key and in stock Next up the voltage max so the voltage max exactly what you think What's that? What's the maximum voltage that you could have as the power supply that you're you're limiting now? It's you know, you're gonna see these in like chunks of like six twelve and then you know fifty and then up to like a hundred That larger the voltage of course the bigger the fuse So if you're looking for price, you know, you might end up at a lower voltage But since size is most important to us We're probably gonna be limited to like that oh six so that that six volt or maybe even eight volt Power maximum based on the size. So actually since our size is the most specific thing we have let's go to surface mount and let's pick from the Package size 0805 which is 2012 metrics. You can see these get very large and there's also Through all size ones and there's whatever there's these like gigantic chunky square ones So let's let's apply. Okay, so now we're only gonna be looking at the 0805 ones So the next thing is Right, so you can say we can we can pick the voltage max But since all of them are above our maximum voltage, which is USB, which is five volts, you know We actually can leave this alone So the next question is the current hold and the current trip and that's actually kind of that that the most Important things you're gonna want to think about in general the current trip is two times the current hold Now like I said, it's a this is a temperature coefficient device is very temperature Dependent so you don't want it to add significantly different or poorly at like high or low temperatures You want it to be somewhat consistent. So it's not like when it hits That number it'll immediately trip. There's gonna be some variation, right? So you want to think of Based on the usage current how you know how much Current is gonna be going through is it continuous is it spiking hold is like your continuous current and trip is like when it spikes up to That that's when it's gonna shut off now technically For USB 500 milliamps is considered the standard hold current I will say though that you can you can get ones with higher or lower So let's look at 500 milliamps to one amp and that's what the whole cuz it's like that's our like consistent Power draw. Why would you even need that much for a keyboard? Well, maybe you have a lot of neopixels on it You have an OLED screen. You have a buzzer like a lot of things are adding up before you know it You're at about 500 milliamps But you don't want of course to have the fuse so low that people are tripping it just on usage because they'll make The device seem really flaky So then let's apply all Okay, so next there's there's thickness which I don't really care about There's the Resistance post trip. There's you know the resistance that the current trip you can see there's it's usually about two times Whatever the hold is and then current max is like how much you could force through it before it gets damaged Time to trip is you know how long that the high current before it actually trips Most of these are about you'll see there. They're all pretty much about Point one to point three seconds. They're not instantaneous, but they're also not super slow Just make sure that it won't damage your board Okay, and next up and then of course if you need Overvoltage protection. This isn't do overvoltage protection. This is over current protection If you need over voltage, there are different input filter chips that you can do that, you know, they're they're they're safe for a very Wide range of input voltages or negative voltages and they won't let current through unless it's like the right level And sometimes sometimes they also have current limiting as well So this is this is good for usb where you're you're never going to have something over five volts coming to usb So you don't have to worry about protecting against overvoltage is just over currents All right, so next up. Let's uh look so yeah, so you've got 750 milliamps. We've got 500. We've got one amp Really, it's up to you. I think I'm going to go with the 500 milliamps It's it's it's a safe amount, but that's also again the standard So having this be compatible with the pro micro if it's doing 500 hold I should do 500 hold So you do that there's about seven options remaining So there's a couple of what's really nice is yeah, these are generic so you can get them from borons And from little fuse and from bell fuse As you can tell by the stock numbers Bell fuse is super popular. You know there's 135 thousand of these in stock right now This is a nice rendering And uh, you know, it says 20 weekly time, but there's 135 thousand in stock So like we're we're good to go and these are only about 10 cents a piece So I didn't want to pick up these. Um, they're good, but then again, don't worry about it There's always fuses available in that package from other suppliers So, you know, if you're worried about like shortages or something just make sure you Have the part numbers written down for all the alternatives But this one seems like it's going to be fine for quite a while That's the great search