 To be 720 and welcome display data. Hello everybody and welcome back to my desk. It's a Sunday night It's engineer clock now eight o'clock eight o'clock and I'm gonna check in what I've been hacking on this weekend a lot of prototypes I got a PCBs in and so I put together some protos And I'm ready to order PCBs because you know I get test them and I find my mistakes and I fix them and I order stuff so Let's kick it off with Let's die right in first revision. So let's go to my computer so I can show what I've been up to so Oh Don't close the one thing that you wanted to show So the micro lipo is a pretty is a fairly old design. It's a lipo charger that uses the mcp-73 831, you know, it's a SOP 235 LiPo charger works with you know any standard 3.7 nominal 4.2 volt max LiPo or lithium-ion battery the thing I really like about this is it's got You know a tri-state status pin that can tell you what it's charging when it's done Which I really like about this charger chip. It's also inexpensive. It's available. I kind of use on everything It's never done me wrong So it's a good charger chip and you know this is a simple board that you know it can plug right into a USB port And so I actually you know keep these around handy all the time because they use them to charge batteries When I'm working on projects and I was about to reorder the PCBs and whatever I'm reordering PCBs is also when I am like Oh, you know, I should maybe update or revise it if I can So what I did is you know, I looked at the design and this is a design back when I was using 0805 parts majority majorly Majority and I've kind of changed over to doing 0603 parts And so I was like well, you know, I might as well like change the parts over to 0603 and at the same time I really wanted to Update this design because one thing I didn't like is that there's this little jumper on the bottom that you would solder to Change it from point that's sorry from 100 milliamps to 500 milliamps because you kind of want to have If it's a small battery you want 100 milliamp rate charge and for larger 500 But I want to change that to a switch and so I did that by You know as I squished everything to 0603. I was able to actually make enough room To put in a slide switch and the slide switch instead of a jumper lets you select between You know 100 milliamps and 500 milliamps you can see like the one here in the five here So let's go to the overhead and I'll show it really fast So one thing, you know, it's like well, you know, whenever I do prototypes. I'm like I made no mistake This is perfect, right? Well, I like swapped a Polaria in the battery It's like the one thing like not to do but I did it anyways. So this is What it looks like You know nominally and when it's not plugged in I can actually like that both LEDs are on it kind of tells you that It's not charging and then you know, I've got this battery pack here I plug it in it turns red and you can see This is about point one amps. So this is the 100 milliamp setting and then if I switch it It changes over to about 500 milliamps a little bit less because I use a 2.2 Care resistor. So it's kind of nice because you can now switch between the two Versions and when the charging is done the green LED lights up So, you know, what I do is basically when when I'm ordering The PCBs, you know, the next time I order I'm gonna order this new design and then we'll just switch over And and replace the stock. So I like to do revisions like especially when I'm what it's time to we order PCBs That's what I'm like. What did I want to change about this? It's a good time to like clean up and update Okay, so Next up staying on the overhead My teacup here We got the step switches that JP really likes these are like tier 808 style step switches, they've got Nice clicky behavior built in LED, but they're not super breadboard friendly They actually are on a point inch point one inch spacing But like they don't fit into a breadboard because of like, you know, it's not always breadboard so I Finally got around to designing a little PCB breakout I think I showed this off a couple weeks ago where this it's very minimal because I wanted it to make it so you could plug in side-by-side to make like a little Sequencer controller so this plugs it so I followed the The data sheet and it does fit it's a little bit of a tight fit Which I thought some people might struggle with so while it does work for my final design I enlarged the holes all by about like 10, you know, 15 percent but this is the Step switch so, you know, this is the one that I soldered together And I just have it running a little Arduino sketch where when it presses it detects it turns on the LED And then I didn't wait the code to support the second switch, but you can see mechanically You know if it's soldered in it would be right next to it, which is which is, you know, perfect It's actually exactly half an inch apart so you can have multiple switches and So this will come in a let's see if I can load up the Yeah It's under step switch so Because like, you know, I don't want to sell an individual PCB I actually panelized it and I'll just sell it as a panel So like the entire panel will be sold as one product because it's like it's the cost of like one little PCB and six PCBs It's like it's the same so you might as well just get a pack of six We sell the switches and packs of three and I figured like six is like, you know, two, you know Most people don't want just three. They want a little bit more or whatever so I just tossed in six for for good luck and And You know, I just I just tiled them up and then they're v-scored so you break them apart You would have to solder them in but You know, it's pretty easy in this way. You could stack them up next to each other So that's that's already done. You know, I put this together. I tested it and then, you know, of course I did the nice Look at the back You had a nice silk screen that we talked about last week using Penguin which is Philby's tool that lets you put nice fonts on your PCBs. So that's that's that and Then third up. I've finally gotten to Testing out this is the this board quit here. I'm testing out the TCA 95 40 oh, this is Okay, the the PCA slash TCA 9584 which is a multiplexer, but this one's designed for STEM IQ T. So this prototype came in as well and You got the I've got a little sketch that you know I wrote that's a I squared C scanner that will select each port for you And scan it so it's a very easy to test So then If we go to the overhead, I'll show my little testing jig So I've got the same, you know Metro mini with the STEM IQ T port Hooked up to this multiplexer this eight port multiplexer and then I Can switch between each port and you know, I'm just testing it by seeing like, you know, can it detect the Sensor on each port and then this is the logic level Converter which will not show this one doesn't have a regulator. So you'll see the Difference, okay, so with this one You can see the LED brightness changes if I'm at five volts versus three volts I actually changed the final design before I said that the PCBs just to change this LED to be Powered from this switch. So it also will dim or brighten a little bit based on whether it's three volts or five volts We can do shifting, you know, if you have a five volt regulator and then you want to use like quick boards Which are three volt only Yeah, you just set it to three volts with the switch And it would be regulated and level shifted. So if we go to the computer Thank you So you see it scanning it always will see address 50 because that's the address of the Multiplexer, right? That's always gonna be visible But then as I unplug and plug into different ports, you'll see, you know, it goes from port one to port two I can do port three Four Six Seven and eight only thing is like, you know, the these static UT connectors, they're not like fragile but like Asking somebody to test by plugging in all of them It's gonna take a really long time like it just takes time to plug it all in So, you know thinking about how to design the tester for these I I Added test pads on the bottom. So each I scored C port the SCL and SDA for that port, you know port four They're going to be available as test pads on the bottom And so my tester will have Pogo pins that reach up and poke them And so you won't have to plug in eight stem acute ports, you know The only trade-off is of course that way you're not actually testing the stem acute connector However, I've had almost no problems with those connectors like, you know, and we've sold like easily half a million You know Connectors on all of our boards like the hundreds of thousands of boards and each one has two connectors It's very very very rare like once You know every four or five months somebody will say hey There's like a bench pin or or something went wrong with the contacts really They're very reliable the thing that's most likely to Be an issue With this board is these Pins here will short like that's you know or like there's a part that's a skewed or missing But really like the issue that you know just from experience I know that these these T-SOP pads love to bridge a little bit or the T-SOP is a little bit off-center And so that's what you want to test So I'm willing to speed up the test so that it's like what I'm testing is the is the most likely failure point then Taking a really long time and also Adding the risk that when people are testing and they plug in the stem acutee. They might plug it upside down and like jam the pins That's a little bit more risky. So this is this design and then Again, I'm going to Okay, so development and then this is a multiplexer and then this is the This is the I squared C Now I keep tea so there's so many boards So I'm also running penguin on it before I send it out I'm actually having a really good time like running penguin because everything looks like so just like fabulous This is the You know the bottom silk With a lovely font and I can you know tweak this You know move this around. There's a lot of you know vias on the bottom, but I think it'll still come out. It's pretty big font and You know, maybe these can go down here So you can see it's like so easy to rearrange as necessary Really that the script so far is you know, it's worked on everything. I've had to send Send through it. So hopefully if people are trying it out and getting some nice fonts on their designs So those are the three boards that I worked on today. So there's any questions before no, let's keep moving Okay, let's do the great search. Okay, cool The great search brought to you by digikey and Adafruit every single week lady to use their power of engineering to Help you find all the things you need lady and what is the great search of the week this week? Okay, so this week this is actually I almost got made a mistake in this design And so I was like whenever I almost make a mistake Well, if I made a mistake, I usually don't catch it till later But then I'll do a great search about it But this time I caught it before the error occurred which is I have a design that I'm doing that uses a slide switch a Vertical slide switch that is used for power selection. So Open up the original one Okay, yeah, it's my computer. So The way that this design works is you know, I'm using this I squirt see multiplexer and I'm moving in the signal from your five volts Controller to possibly three volts five volt or three volt peripherals So I'm adding like a level shifting thing But not only my level shifting the signal but I'm levels, you know I'm power shifting that the connectors themselves what will provide power to The individual peripherals on the air squared C bus will also be either three or five volts So it's not just signal level. It's power level And there's eight ports. They're like, you know, that's the power adds up. I'm using the AP 2112 3.3 volt regulator this regulator. I really love it has about, you know, 500 milliamps output From, you know, three to five volt very low dropout as well, which I really like so you have three volt in Won't drop out too much Even at fairly high current. So it's a very good regulator. It's nice and stable But one of the things to watch for is when you are Using a switch for power not signal because again a lot of people use buttons and Slide switches to signal something, you know, send a digital signal into a microcontroller or enable pin or, you know I showed the micro lipo it's it's switching a resistor on the IRF pin of a LiPo charger the amount of current going through and the amount of voltage going through the switch is very very small It's like, you know, maybe even a milliamp, maybe three to five volts. It's it's fairly pretty much negligible The issue is when you're doing something like this and you actually want to switch power through now, you know If I'm switching more than 500 milliamps, I wouldn't go for a mechanical switch Especially a surface matte one I would use You know some PFATs and I would you know make a proper, you know Solid-state switch not a mechanical switch But in this case, I you know turns out I can kind of get away with this By doubling up the switch, but also by making sure I'm speccing the right kind of slide switch. So let's to the slide switch just to Show what it looks like You know, it's You know, I don't have to use the exact same footprint, you know in this case I am but I want it to be vertical so I want it to be pointing up You can slide it back and forth easily with your finger And it'll show that this is the same switch here So I you know, I particularly like this switch. I found these are very mechanically strong They they're easy to switch with a finger no matter how big or sausagey or smaller fingers are And they have fairly good availability for voltage and current But you know, we talk about jelly bean parts a lot and you look at like tactile switches and you can connectors Jelly beans are jelly beans, but you still have to look at the ratings It's not just because it looks the same doesn't mean it's the same so Let's go to digikey. So what we want is a slide switch and we've we've looked for slide switches. We've looked for Side slide right angle slide switches. We're gonna look for again at a top slide switch notice the nice images I like new new search style come in and digikey with pictures. So we want a slide switch We want active one thing that we you know, I'm not gonna look at because it turns out to not matter so much for this But shorting versus non-shorting also, you know, that's it just because it looks the same doesn't mean they're all Sliding which is non-sliding. Okay. We want surface mount and we don't want the right angle We want vertical pointing up So that actually gets rid of a lot of design So now we can look at some images and be like, yeah, you know, this is kind of what we're looking at here Like this particular looks this is what I often use for some designs So here's where you want again look at the rating if you're using it for signal We're eating doesn't matter because there's almost no power going through it But we're we're putting power through so the first job. I do want to have the voltage be above Four volts because I want to switch five volts signal on and you'll know that, you know, some of these are 12 some these are 6 But there's also, you know, this one Which is looks very nice, but it's only four volts so Sorry gotta go can't have four volts because we are switching a five volt power through Okay, next up I only want, you know, normally stocking parts because I want to be able to get it and Then let's look at what's available All right, cool, so you'll see some of these, you know, 100 milliamps some of them 300 milliamp We're kind of like the 300 milliamp. The only thing is I do want it to be You know, one of the things I'm doing here is It's a DP DT Yeah, which means there's two independent switches and each one has the contact rating I Double them up. You see I parallelize them which on the board looks like so and That means I can get double the current and the voltage is the same But the amount of current going through the switch is is essentially doubled So you do the same thing for relays by the way Just be aware like with relays that you know in these switches, there might be a slight, you know, microsecond delay between Connectivity just make sure that there is no There's no risk of the cross connection Okay, so I was going to Look for current. So, you know, I do work to have You know at least 200 or 300 milliamps per Switch because I'm going to double them up to 100 milliamp is a little bit too low Because even doubled up that's 200. I really want to be closer to 400 or 500 and then Let's look at what's available by price So there's a couple options here So this one's right angle. So, you know, even that's a kind of a nice switch not going to use that This is a DP 3t, which I don't want This one is kind of nice, but it's spd t which means I don't get to double up the switch So actually I'm going to go back and select only DP t style Okay, cool. So now we're talking. So these you know, they're they're I don't actually know 100% that they're exactly Pad compatible. I have to you know, I'm gonna have to look at more detail in the data sheet to make sure that the switches fit on the pads and if not it adjust the pads and the Footprint, but there's a couple good options here You know this one particular ironically, you know the cheapest one the one that they have the most in stock is actually pretty Nice, it's going Which means that it has good mechanical stability, which I really like like it's there's a look at the 360 of this It's got you know the pins that go out to the side So mechanically stable It's got a nice long actuator. It's pretty simple but you know effective and then it's six volt 300 milliamps rated Which is also nice and if you look at the day, I will I'll say one thing Really read the data sheet by the way to make sure because sometimes the contact ratings differ Based on the voltage like for example here It turns out you can actually go up to 30 volts DC, but you'll only get a hundred milliamps So just just be aware like the rating, you know that contact rating will it it's actually dependent a little bit not on voltage and current, but you know the The product of the two so be sure to watch out for that and also tell you the electrical life 5,000 cycles, which I think is fair. This is gonna be switched all the time and You know seeing K makes pretty good switches I've used them before and you can see, you know, they have a through hole version and Then this is basically the same switch as the through hole. You see they just bend the like the leads out And then check the footprint and then they also have a version of this switch Which is Hold on Let me find it this one same switch, but No, not this one that not this one. They're all the same this one. It's still DPGT, there's two independent switches, but the leads are bent under so You know mechanically not quite as strong although it's still you know the pads underneath there are still long enough I feel like but if I need a little bit more space if this switch ends up being bigger than I expect I can go with this version. So it you know conserve space on the PCB But for now, I rather like this one and it's it's really expensive to you. It's you know, like 40 cents in quantity Six volt and 300 milliamps. So You know, one of the things that I do is whatever switches I use You know, I try not to have multiple versions of similar looking things with different ratings because I find that that's Just accidents are waiting to happen, especially with rework or repair or whatever So, you know, even if I have boards that are Using a slide switch for signal. I would still use this hefty power rated switch Just so I only have to stock one item So let my great search pick That's a research Okay, here's a couple things that came in yes, I Think this is a for you your folders say TCA 9548 Hey, but your silk says TCA 958 4a yeah, I probably I've been transferred the yeah and the four I do that all the time Do you need me to tell you that after no, I'll remember one thing actually to note is it uses the The folders the TCA and I'm using the PCA Yes, the folders called the TCA But the product I'm actually using in the end is the PCA which is the TCA does 1.8 volt to 5 volt the PCA does 2.6 to 5 volts and since Stem IQ T boards never go below. They're only three or five and You can't get the TCA right now. You can get the PCA like, you know, it's a little confusing, but I don't know these words yet. So it's okay Does a PB 86 have a resistor as part of the circuit or is that needed on a breadboard? You'll want to add that on a breadboard. It's not added because I Did the math of like well, I could send it through the pick in place But it would like add so much cost and effort That I thought I would just have this basic breakout That's a mechanical breakout and then people can add the resistor based on whether they're using three volts or five volt logic Or a 12 volt logic, you know, I don't know or power for their analog circuits. All right And that is the desk lady to this week. Thank you everybody. I thank you all throughout the week We have a full week of shows and more. Thanks so much for spending some of the Sunday night with us. We will see you soon