 The Great Search brought to you by Rude and Digikey, where Lidea uses all of her powers of engineering every week to show you how to find the things in the world on digikey.com. Perhaps the biggest, best place to get electronic components in the world, what do you think anyways? Any who, Lidea, what is this week's Great Search? Okay, so this week's Great Search is while I was designing, you know, whatever I was designing, that's kind of what makes into the Great Search, because it's like, I'm actually searching for this and I should do it. This week's Great Search is a 8-channel buffer transceiver non-inverting that I added onto the Scorpio feather that will convert 3 volt, 1 megahertz signal, so fairly fast, signals from about 3, 3.3 volts safely up to 5 volts. The 5 volt signal comes from the USB line, the microcontroller runs on 3.3, I want the output to be 5 volts, I can't run the microcontroller at 5 volts, I run the microcontroller at 3 volts, I output the signal and I buffer it up and out into a pretty 5 volt level signal and I want a 8-channel buffer that does this nicely and cleanly, so let's go to the computer. Okay, so this is my schematic, these are my signals coming in, 8 signals, I'm using, there's actually a couple chips that do 8-channel, there's like literally buffers, this is technically a transceiver, the 74AHC245, and most importantly is I need it to be really small. Sometimes, for example, if I, let me just, for fun sake, I'll show the T-SOP, the T-SOP would not have fit, so this would be the T-SOP version and I'm already using a 402 resistors, there really, there was no space, I had to go down to a QDFN, and thankfully there are QDFNs of 74 series logic, but I never showed, you know, I talked a little bit about Norgates a while ago, but I never showed how I specced this transceiver because, you know, the 74 just means like it's a logic with the family, the TiLogic family. 245 is the name of the 8-channel transceiver, non-inverting transceiver, but the A-H-T, A-H-C-T, hold on, it is the A-H-C-T, actually all sort of stands for stuff, and you can't necessarily swap out different versions. The A-H-C is I think high speed, and A I think means it can run from 3 to 5 volts and can take up to, can take voltages that are above the VCC if necessary, so it's got that, can go from 3 volt to 5 volts or 5 volts down to 3 volts, and the T is transistor level input. If you get the A-H-C version, that is CMOS, and when you add the T, it's transistor level logic, and I'll show you in the datasheet why you want transistor level logic. That's actually a tip to Paul S. from PJRC. You can get away with running the non-T version, but it is good taste, and it's at the same price to use the transistor level logic version because it does make a difference, you know, if your voltages are a little marginal, it can make a difference. Okay, so let's go to Le Dijiqui. That's the front side. Yes, sorry. Le Dijiqui. And I want to look for a buffer, oh sorry, buffer transceiver. Sever, I before E, E before I, should I spell it right? Yeah, so there is a whole section called interface drivers receivers transceivers. They're all kind of the same thing, kind of sort of, maybe, you know, again, I happen to know that I want the 245 series, but I'm showing how you could kind of like reverse figure that out. Okay, so for this, it's going to be an active design, so I only want active parts. It needs to be small, so I only want surface mount, and I'm going to apply. Next step, I only want stuff that's normal stocking, and I'm going to for now just exclude marketplace products. So that just kind of reduces it. And then I thought I clicked active, but maybe I didn't. I'll say that the new thing where it previews the things for you before it does them has confused me a little bit. Okay, I think, oh, you know what, I'm actually in the wrong section. There are two places. I went to drivers and transceivers. I meant to go to buffers and transceivers. Silly me. Sorry. That was interface. See, you're learning something from me. I went to interface drivers, transceivers. What I meant to go is logic buffers, receivers, and transceivers. So silly me, but now we're here. And yeah, now you're seeing there's 74 series logic here. So yes. Okay, so again, I'm going to go for active, and I'm going to go for normally stocking, and I'm going to exclude marketplace. Okay, great. So next up, I want non-inverting. Inverting, of course, flips things over, but I don't want that. I want signal in to be signal out. So I'm going to select buffer and transceiver, both non-inverting. Exactly the opposite of what I just clicked, which is ironic. Okay, so next up, I want surface mount. And now we're... So technically a transceiver, the data can go either way. So you could use a buffer. But in this case, one thing I want to do is I want to get to have eight bits of data. And it can be a little confusing, I'll say, because sometimes there's two things here. There is number of elements, and that goes from one to eight. And then there's number of bits per element that goes one to 10. And you might be like, well, how do I want one element with eight bits or eight bits with one element? You try both. In this case, I already looked it up. So I want one element with eight bits. Which is a little confusing. So let me apply that. Okay, so now you're seeing... We're seeing a lot of 245s, because that's kind of the classic part number for the eight-bit non-inverting transceiver. Okay, so next up, remember I wanted to have that small package. The T-SOP was too big. So normally I'm not as picky about the package, but this time I'm skipping over all the T-SOPs and the T-SOPs, and I'm going straight for the 20 QFNs. And I'll say there actually aren't a ton of QFN options, but the QFN, you know, it's going to be much, much smaller. It doesn't have legs. A lot of the 74 series logic, of course, started as dip, moved to SOIC, then SSOIC. And then, you know, you can sometimes get it in VGA, or in this case, DFN. So last up, I'm going to do the voltage supply. Now remember, it's the microcontroller's three volts, but I want to output five volts. What I'm going to do is I'm going to power the buffer with five volts. I feed it three-volt logic. Whatever it's powered by is the output signal. So I'm going to make sure that this can be powered by up to 5.5 or 6 volts. And this is where it's like it gets really limited. So there's really only like a dozen options now. And then let's just look at the ones that are in stock. So now there's only 10. And I mess something up. Hold on. Okay. So now there's a couple different versions here. There's like the VHC, the HC, the HC, the HCS, HCV, et cetera, et cetera. And what I'm saying is I'm going to be using the HCT. And the reason for that is if you go to the data sheet. And this data sheet covers both the AHC and the HCT version. Again, HC, CMOS, HCT is transistor TTL logic. And if you look at the... Okay. This is the HCT245. The high level input logic is 2 volts. You can see right here. And if you go up to the HC, the non-T version, it's CMOS. So the voltage input level is going to be much higher. The requirements for it to register is high. If you power it from 5 volts, it technically wants you to give it at least 3.8 volts logic, which if you're running a 3-volt logic, you're not going to get. Now I'll say because I'm a naughty person, I'm going to get coal in my stocking, except I'm not because I'm Jewish. But if I was, you shouldn't assume that your HC logic will be happy with a voltage lower than 3.8. The data sheet specs it at 3.8. It wants 3.8. If you're giving it 3.3, it's going to likely work. So don't freak out. But the right thing to do if you're speccing the part, and it's the same price anyways, is to go for the HC-T version, which has the TTL logic input, which means that the logic input level is the same no matter what the voltage is. And then maybe one day we'll cover the difference between CMOS and TTL logic. Trade-off. Use a lot more power on the TTL logic input. So down side, but if you're driving 8 strands of neopixels from this board, you don't care about power because one neopixel uses more power than this transceiver. So not a problem. So this part is quite nice and better off, it's in stock. Best of all, it's in stock. So I ordered a bunch of these. And there's a couple, again, there's like the VHCT maybe. There could be others that also can be driven off of 5 volts and can take a lower voltage, but I don't remember all of them. I do know that this one will work, so I'm happy to purchase it. And if it ever runs out of stock, I can always look at alternatives. That's great search.