 The Great Search brought to you by Digikey and Adafruit. Every single week, ladies and gentlemen, the power of engineering to find stuff online at digikey.com. And guess what? It's hard to find stuff. We've been doing this before there was a part shortage we'll be doing this after Lady Adafruit. What is the Great Search of the Week? This week. Okay. This week, I'm looking for a new part that I'm gonna put on my ESP32 QT Pie Divine. Click it on the Pico board. I can show the back of it. The left, left, left, left, left. This one? Left one more. Okay. So the ESP32 is a kind of interesting chip because it doesn't have made of USB. So you've got to add a USB serial converter and that's the second chip, the one in that kind of the middle top there. The ESP32 is the thing on the bottom. So we've got a CP2102 and we covered the CP2102 as a USB serial converter, like a low cost, small USB serial converter. And that's all good. But there's another little thing. Not only do you need the USB serial for RX and TX data, but by doing this kind of funky trick with two NPN transistors, you can use the pulses from the RTS and DTR lines on the USB serial converter to reset the ESP32 into bootloader mode. And this is similar to, if you have an Arduino, the Arduino also used RTS or DTR to toggle the reset line to kind of auto reset the board from USB serial converters. For the ESP32, they didn't connect the DTR at RTS directly. Instead, they have this little transistor, like flippy floppy thing going on there, which I want to analyze and then I've totally forgotten how it works. So let's go to the computer and I will pop up the schematic and I'll show you the part. So this is what it looks like. You connect, there's IO0 is the bootloader pan and reset is the reset pan for the chip. And then RTS and DTR, when they do a little toggle, they will lower the IO0 pan, which tells it to go into bootloader mode on reset and then it quickly toggles the reset pan to set it to reset. It comes out of reset, IO0 is still low. It knows it should go into bootloader mode. So the only thing is I need to get a dual NPN. Now I've got N-channel FETs here, but you can't use N-channel FETs. I've never actually tried it, but like every schematic from expressive users to NPNs. So I'm gonna show you the NPN. That said, I do like the dual BSS that we use on a lot of our boards. It's this part here and it's nice and small. These are 0402 resistors. This is a TSOP6, also known as a SOP363. It's finer pitched than a SOP236, which is a SOP23 is, I'll show you. So this is a SOP23 size. So it's significantly larger. I'll use a SOP23 for a power supply, but for something that's not using a lot of power, like this dual FET thing, a SOP363 is perfectly fine and you actually can solder them by hand. Like they're fine pitched, but they're 0.5 millimeter. So they're not gonna kill ya. You can hand solder them. We use them by like the hundreds of thousands. Every STEMIQT board, we include a dual FET to do the level shifting for I squared C. And so we stock 1,000, 1,000 of them. But again, those are BSS138N channel FETs. This time we want dual NPN. So let's go to Digikey. First up I wanna mention, so this is the dual FET that we use. BSS138BKS, we have a quarter million stock because we actually go through like 10,000 a day easily. Because there's like two or three on like almost every single board that we make. So this very small part, and this is the part, I actually couldn't remember the name of the package. So what I did, I was like, if I want something in the same package, I'll actually look up what Digikey calls the package and then it'll just make it a little easier for me to find the part. So this is called, this has multiple names and that's not unusual sometimes when they get these small chips, they have different names. So this is called a 6TSOP or SCE8 or ASAP363, so good to know. Anyway, so what we want is a dual NPN. Pardon me. There's a couple NPNs, just be careful because I actually accidentally went to single. Like I went to single first when I started searching. You can't, you have to go to arrays. And NPNs come in a couple different configurations, so it's not a big deal, just watch out for it. Sometimes they do you a favor by connecting stuff inside, but we want two completely separate NPN transistors. And again, for most of our ESP32 boards, we just have two SOT23s, but we just don't have any space on this board. It's so small, I have to go with the SOT363. So let's go with in stock active, and then let's look at that package. So again, I like the package that I've got the BSS138 in, which is a 6TSOP SCE8363. There's probably smaller, but this is pretty small. I think like a, you know, UDF it'll be smaller, but I like things with pads, you know, for stuff this small. Okay, so let's apply. One thing to, because I picked something with six pads, I sort of solved one problem, but if you look at the configuration, you can get common emitter. Common emitter means the emitters to kek together. This is really good for differential measurements or amplifiers. There's quad, of course, and then there's matched pair and non-matched. Matched pair, like it means that they're guaranteed to be within a certain percentage of the same VBE, like whatever, like the amount of current that they're gonna pass in the voltage offset you're gonna get, like they're gonna act very similar. And again, that makes it better for differential signal measurements. In this case, it doesn't matter, because again, we're using them totally separate, but also we don't want common emitter. So I don't mind looking for matched pair, but usually you have to pay a little bit more for matched pairs. If you do synthesizers, you're gonna constantly be doing matched pair stuff, but I'm not doing synthesizers, I'm doing a cutie pie, so that's cool. Okay, back to this. Once I select that, yeah, there's only matched pair, non-matched pair, which I don't care about. And then when I go down here, I sort it by price just to see like, okay, well, how much am I gonna pay for these? And one thing I noticed is that the ones that are the least expensive, like these Pum-X2s from Nixperia, they have a min-quantity, and there's no way to not select. I don't know that there's a way to select something that doesn't have a min-quanty, but if you click here, you can only buy this by the real. Like if I try to buy 300, it's gonna say no. So that's not like a bad thing, like I might use these, but if I'm gonna get samples, which is what I'm doing right now, I wanna get something where I don't have to purchase a large quantity. So for example, like this has a minimum quantity of like 4,000, and I don't wanna buy 4,000. So what I did is when I got to these two Ansemis, this BC-84-7, these are the ones where I saw like, oh, they have plenty in stock. There's two versions, there's one from Panjit and there's one from, there's a couple from Panjit and one from Ansemie. And these have a minimum quantity of only one. So it's tough because the other ones are much less expensive, although it's a minimum quantity and maybe at the minimum quantity, or the quantity I need, it'll be about the same. But I'm getting only samples right now anyways. So I order the samples when I get the PCBs on order. So by the time the PCBs make it to me, I got all the components. But these are in stock and they look just fine. So I'm gonna pick these up, I'm going to try them out. And nothing really beats just soldering them into a circuit with an ESP32 and just checking that it works. But I'm pretty confident it will. Like the ESP32 Reset Circuit is like very well tested and tried. So even though I've never tried this particular transistor, you know, they have a, the voltage limits are reasonable. The current collector, the current, max current to the collector is reasonable. The DC gain is reasonable. Everything, this is a very jelly bean part. So no reason why it won't work. So this is gonna pick up 50 of these and get ready for when my ESP32 QDPI arises. The one part that I don't already have stopped. And that's a great search.