 The Great Search brought to you by DigiKey and Ada Frith. Thank you DigiKey. Every single week, a lady had to use a power of engineering to help you get to find all the things you want to find on digikey.com. Take it away. Okay and my hair is like DigiKey red, right? Okay, so this week I worked on this design which is a underboard for, sorry, an underboard for the Raspberry Pi Pico. And I was saying like, oh, you know, I have a STEMQT connector and a reset button, so I squirt scene resets easy and then I have an enable switch. But I also wanted to add battery charging because especially for the Pico W, it's wireless. Maybe you want to have like a IoT thing that runs on a battery with battery charging. And so I kind of borrowed a circuit that I use for the, let me get rid of the sidebar. It's so big, especially in 720p. It's very noticeable. Okay, sorry. Okay, I borrowed the circuit that I use for the feather boards, which uses an MCP73831, has two LEDs, one for charging red, one green, which is like done. And then it's capacitors, you can set the charge rate with a resistor. And then there's like a pass transistor. But I realized I never actually covered lipo chargers. And so even though I use this one, by the way, there are a lot of other options on DigiKey, but even this one has a lot of like, especially during the part shortage, you got to really watch out. Not all numbers are the same for this part. There's a lot of like dash XYZ. And that's what I want to watch out for. So let's go to DigiKey and search for battery charger. So what we want is a battery charger that will charge 3.7 nominal, 4.2 volt max batteries from USB, because that's what we're getting like five volts in. And I want something inexpensive that can also, it doesn't require iSquared C to set up, it just is set by a resistor. Because a lot of the really fancy chargers have like iSquared C or their 1Y or whatever. I don't want, you know, whether you can do all sorts of configuration and like also monitors the battery. I want something like cheap and easy. And again, resistor set. So you set the resistor and then here I have my little guide that reminds me what you set it to in order to set the charge rate. And you know, I'll be honest, actually, this says one amp. This actually just charger actually can't do one amp, which we'll also talk about there are some other chargers that can. So let's go here and then we'll look for battery chargers. Okay. So there's like big battery chargers, there's battery management, but we want battery charging chips. So let's go here. So there's there's 3000, there's quite a few. And, you know, they come from anything like DFN and SOCT to like they can get a lot of pans and very complicated, you know, they come in BGA also. So let's just try to pare down this massive number. We're only going to look for the active items. And we're only going to look for ones that can handle one cell, because there's some that do two or more. And then I'll also get I'll pick up the dash as well. And then let's just, well, we only want surface mounts. And let's just say we only want in stock. So it's available to purchase now chip shortage is kind of over. So basically if it's in stock, that means it's going to, you know, any, if it's not in stock, it means it's probably like not available. And no marketplace just because I don't want to have the double entries for externally sold parts. Okay. Next up. So the battery I'm using is a lithium ion slash polymer battery. And there are other chemistries available, but pretty much, you know, I'm going to pick up the dash just because who knows, lithium ion and polymer, lithium iron phosphate, I think it's something different, multicemistry. I actually don't want any of the multicemistry ones because those are always going to be more expensive than just a dedicated charger. And then I want to also set the voltage of the, I don't know if we can set the voltage. Well, let me do this. Let me just filter on the on the chemistry. Okay, good. So that's much, much chiller. Okay. So next up, charge current max. Well, I really feel like if I'm going to charge these batteries, it needs to be at least 200 milliamps. And, you know, I can go higher, but honestly, like no charger that's going to be affordable is going to be over like three amps. And then the battery pack voltage, I want it to be, of course, these batteries that we're using. So these are lipoly batteries. You know, if you're using other batteries, you know, go to town, but the ones I'm using, I think I actually call them lithium polymer, but sorry. Great. These are 3.7 volt nominal 4.2 volt max. And so watch out because it's even though it says 3.7 volts on the battery, you don't actually want 3.7 volts. You want like 4.2. So I'm going to pick also the ones that can do, you know, whatever, but I definitely don't want the ones that do higher voltages. This is all I want 4.4.2. And then interface, I actually don't want I squirts your USB. I want something that is again, a very simple interface. So just GPIO programmable and this will reduce the number quite a bit. Yeah, now we're only getting like, okay, there's one or two, one or two, one, two or three cells. Okay, now I think we're good. I mean, the voltage, you know, I don't care as long as there were five, all of them are over five. Current max, I think is okay. So let's look at some of the options. So we've got the mcp 738 standard option. And, you know, they have a ton in stock. There's also the 832. And they have them also in DFN. But there are other families. I'll say the BQ series from TI, they're quite good. These are, you know, they also have a charge led. You can set the current with a resistor. Some of them have like termination timers, like how long you wait before you time out or whatever. They also have a power, good output. So, you know, the more pins you get, the more options you're going to get. And this also has a temperature reading, which I'll say, you know, if you're charging at a higher, if you are going to have people with batteries that are charging at a very high rate, like one C or above, it's not a bad idea to have a temperature monitor, especially in like a production product. For this board I'm making, it's very simple. It's like low cost and the charge rate is already kind of set quite low. So I'm not worried about it. But a thermistor, a built-in thermistor battery pack is never a bad idea. So one thing I'll mention is the battery charger I use on that board, that design does not have a thermistor built in. It's a good idea, especially if it's going to be used outdoors, because at very low and very high temperatures, you do have to change the charge rate. There's also, ST has, you know, a nice low cost battery charger. One thing that is nice about this one is it does up to 800 mA, which again, the charger I'm going to show does not do 800. And it's very simple. It just has like LED program power in battery. It's like there's something quite nice about it. And I like that it has a little bit higher input supply voltage max up to 10 volts. Not that you should use 10 volts, but like sometimes I've seen people like they plug in like some random off-the-shelf, you know, USB power adapter and it like kind of floats a little bit above five volts. And sometimes it can actually get popped. Kind of weird, but it does happen. One thing that I'll say that I've never seen is a battery charger chip that is reverse battery protected. Which would be kind of cool, because I do one of the things I end in this small package at a reasonable price. Because I do see a lot of customers, they end up, we warn people like 8 billion times do not buy batteries from Amazon that are the opposite polarity. And then people are like, I plugged in this battery that I bought from Amazon. And then I realized it's reverse polarity. Did I damage it? And I'm like, yeah, it's dead. Like it's like, but I unplugged it within like a minute. And I'm like, it's done within like 10 microseconds. You can't unplug it fast enough. That'd be cool. If anyone knows of a battery that does that, you know, or a battery charger that does that, let me know. But this one is nice because it does 800 milliamps. But the one I tend to use is this, let me get the part number quick, 73831, which is available in, it's kind of the one they have the most of. And there's a couple of different ones in this family. Or first off, they have a DfN version if you want smaller, but there's a 31 and the 32. And then also, there's like these letters afterwards. And you do have to watch out for these letters. So one, there's the difference between the 831 and the 832 is the 831 has a status pin that can, yeah, so this is the difference. The 831 has a push pull output on the status, whereas the 832 only has a open drain pull down. Why does that matter? Because in this case, on this board, not every board that I use some feathers, I don't use two LEDs, you can on the 831 only have two LEDs, one for charging and one for completed charging. And then it floats in the middle when there's like no battery detected. Whereas the 832, it only does in charging, like there's only the orange light, there is no green completed light. I don't like that you can have both. So I tend to use the 831 because I like to have the two LED option and I only want to stock one part. Next, if we go down to the product identification, there's a lot of options that you'll see. So you'll see mcp7831-2ci, 2ad, 2dc. You'll have to watch out because they're not the same. One, the regulation voltage. The T is just a taping wheel versus a tube, I think, but the regulation voltage is that first digit. So if you get the 738, 73831-3 or dash 4, dash 5, that's going to have a battery packed voltage that's higher than 4.2 volts. Why would you ever get that? There are some batteries that have anodes that are a little bit higher. They're not low cost, a little bit more expensive, but you see them in some automotive projects and I've seen them in skateboards and stuff. They have a slightly higher voltage due to the anode cathode chemistry. So they have a little bit more power you get out of them to a wattage, but you cannot have the regulated voltage here be higher than the battery pack where you could damage it. You can't charge a 4.2 at 4.4. You can't charge a 4.4 or 4.2, but you won't get all the power possible out of it. Second, there is the termination voltage versus the regulated voltage. This has to do with when you first, if you have a dead battery or very, very low battery, you sort of trickle charge it until it gets up to 3.2, 3.3 volts. So there's a little bit of how much current versus the maximum current and then how long do you do it for, whatever. That's not as important. So I've sometimes used the AD instead of the AC because it's so closely related, but do check which one. And then there's two packages. There's the DFN and the OT. That said, the one I use the most, again, it's like kind of the standard, standard issue is like, again, like the 31 and two AC means 4.2 volts. AC is kind of like default termination current, trickle current. And it's in stock and digikies. So let's just put on dark mode. Yeah. And it's in stock. And it's like, you know, pretty cheap, like 60 cents per. Some people are like, why don't you use like the really cheap, inexpensive, like 20 cent chips that are available that are like, you know, from like random asked companies? And the answer is, you really don't want to like go cheap on your battery charger. I always use the genuine microchip parts because like, I know that they have good engineers. The really inexpensive parts, it's just too risky. It's like, if you don't charge your battery, right? It's very bad for the battery and, you know, it can be bad for the person handling the battery. So I recommend getting like a genuine part from digiki. So MCP 73831T to ACI. That's our pick of the week.