 Welcome to this lady Ada. Hey, buddy, and welcome to this lady Ada. It's me lady Ada It's a nice Sunday, and I've been working on some electronics I thought I would just show off what we are working on here some stuff with that we're We got going some things were revising and then we'll do a great search. So let's go The overhead we can do the overhead we can pick up where we left off. So last week we were talking about Tester revisions and so there was a you know tester brains that I use for The tester brains that I use for Programming SWD and RP 2040 boards and seeming some ESP 32 boards and was originally based on a Teen see three point six, but I can't get three to three point sixes and so it's like, you know what I'm going to revise Stop freaking out. I was like, oh, I'm gonna revise this to use a Pico So RP 2040 Pico Because those are really easily available and it's you know about the same speed ish as a teensy has lots of GPIO pins And is Arduino compatible plus we have a very simple USB host stack for like that's bit banged on the RP 2040 She can do the basic enumeration checks, which is part of how I test boards It's actually, you know, it's kind of important to me to make sure that whatever I replace that Teen see three six ways they could do USB host, which is why I'm not replacing it with You know a 70 21 or 70 51 because they can't they can't do USB host But only on the main USB port and I need that USB port to Remain available. I need to be a secondary port So this is the board so, you know, it put it together plugged in the Pico into the sockets plugged in the TFT into the socket and we've got some code at the piezo here the USB host SD card to hold firmware This is you know the two, you know two device under test Connector so like, you know, this connects to say like this Gemma board Which has the same pinout and then, you know, you can Plug and play different Boards depending on if you want to test a feather or a trinket, you know This part stays the same and then this part changes. It just makes it easy if this breaks because you know This my controller can easily get fried or you know, destroyed or a static or coffee spilled on it So this demo code here is pretty simple What's interesting is the RGB backlight. I shouldn't have enough pins to have a full RGB backlight So there's a ws-2811, right, which is a neopixel chip And it's like right under here. You can see it and that's how I'm driving the backlight Then I'm just running, you know, that neopixel pio code on there, but it works wonderfully So it's such a kind of nice gives a nice good constant current color no matter what the parse play is You know SD card because it doesn't have onboard SD and then the USB host so at my computer You know, I started drafting the library called, you know, tester brains that would simplify some stuff So like, you know, I can lcd printf and it will do the right thing and I can say, you know You know if SD detected begin the SD card and you know Kind of just just send wrappers it a little bit to make a little bit prettier than just how you know Trying to avoid having these massive long programs where every pin is redefined over and over again Because I'm gonna be using that same brain PCB and then Over here, we've got the The output and you can see it's like hey, you know, I'm detecting the SD card and it prints out the contents And we're using the SD fat library, which is really great because it has long filing support Which I find really handy because you know, otherwise if people are trying to I Don't know where I was last Okay, well, let's let I'll just restock that USB Chitchat basically the SD card long file name I think I chatted about how we have long file name support, which is really good I like that and then the next step was testing the USB host because again, I like to Test the USB connection. It's a really good way to verify that The right program was loaded because the VAD PID have to be right And also we want to You know program some chips over USB like the RP 2040 There is a SWD interface to the RP 2040, but it's there's a it's a dual drop and it's like more complicated than just you know most SWD programming that we support So we'd like to use the USB interface and on the teensy three six we used mass storage We're not sure that we can bit bang mass storage because it's it's I don't know like how picky it is about errors or Dealing with miss timings and stuff because bit bang. It's like it's not gonna be as super reliable as a native USB stack and so tax looking into porting Pico tool, which is the USB control interface way to Program and communicate with the RP 2040 Mass storage, you know, you drag and drop the file everyone knows that but there's actually another interface Next to the mass storage where you can just send control commands using like live USB, which is what the Pico tool does and What's nice about that is you can do auto resets you can query it You can like do more complicated stuff than mass storage and it's like much more simply defined Like, you know mass storage is a bit of a it was a bit of a stack. There's a lot going on there With the control flow interface. It's not simpler. So, you know, that's the that's the next step Of this, I don't know if the demo I did of this plugging in Came up came across where it enumerates properly. So, you know right now enumeration works and there's actually HID support And are do we know for bit bang USB host, but I Don't know how reliable it is again. It's it's a little bit of a hat. Okay So that's the USB says the the RP 2040 test your brains Currently testing it with AVR programming and then, you know, we'll get More stuff going but AVR is kind of simplest because I like I wrote that code. So I know it's a bit bang. It's very simple So it's SPI It's working, but like I there's a verification issue and I think like I'm not wearing the way I think I Think either my code's really old or like I don't you know, I haven't programmed in the 80 tiny 85 and forever it could be that my 80 tiny 85 programming code isn't isn't checked out. So Or I'm like, and there's something but you know, you have to write fuses and then reset and sometimes you don't do the right order So we'll do that and then, you know, long-term. We'll just end up transitioning to all our testers being RP 2040 based. So That's that. Okay. So next up Doing revisions. So, you know, I've been going through and Qt if I'm a lot of I squirt seaboard You know, and it's it's still going because I've got like 10 15 years of I squirt seaboard and you know I'm slowly but surely going through and Qt fine them. So like, you know, the ADS 1015 I think were some of the more recent ones and then I just I Just did the 80 74 10 was actually one of the last boards before we started semi Qt fine You can actually see it sort of got that it's kind of got that shape and feel of stomach qt But it's missing the connectors this got, you know, this is getting revised as well So when well, these go out of stock will will order the PCBs and implement a new revision But the This board is ancient, I mean, this is product 292 is one of the first, you know pick-and-place products we made It's it's a little chunky and you know used all older Oh, wait a five parts has a couple design decisions that I wouldn't have made these days So I wanted to Qt if I you know if I'm going in and Qt you see it's got the old logo if you're Qtifying something It's like well, we might as well Let's see let's open it up Let's do a bunch of stuff To it, so I think it's gonna be hold on Okay, so this was the older version So, you know you would connect through that the terminal blocks only and there's you know header and there's one mounting hole And then these were all individual resistors and you know remember last week we talked about resistor packs I actually it's cheaper and easier for to pick in place with a resistor pack because you have only one Placement instead of having the head go back and forth four times One for you know actually six six times for each resistor plus I want to add level shifting and boosting So, you know one of the things about LCDs is they are There are three volt LCDs, but there's still a lot that really want five volts logic the backlight Sometimes you can give it, you know 3.3 volts, but the LCD itself really wants to sometimes have five volt Power and there's different chips that are all compatible But like there's no guarantee that the one you have is a certain to work at three volts And so I wanted to make sure that if you're using stem IQT because it can be three or five volts There's no guarantee that you're getting a five volt power through Um the stem IQT port because you plug into your qt pi esp 32 three volt power three volt logic and so I added a little Um Charge pump converter, so this you know, it just gives you again 100 milliamps at five volts But you only need 500 you know 100 milliamps. You don't need that much current that very power efficient But if you're using a character lcd, you're probably not worrying about power efficiency so much Um, it still has the terminal blocks at the same location Um, which meant you know, I can put one qt port here and then this is the level shifter, right? Because it's three volts that convert it up to five Um volts it's actually backwards than usual, right? Usually it's like Input can be five and then you reduce it down to three. This is like input can be three and I bring it up to five Um, since the level shifter up to five volts the little booster gives you five volt power And then I actually had a little bit of a spot here Which was originally Just empty turned out, you know, this is not a bad spot to stick a secondary Stem a qt port which is kind of nice because it'll it'll stick down past the lcd I still have the address pins And then you can see I replaced the um individual resistors with a resistor pack and then Um, this is a little bit of a hack. It was originally this was one transistor But because I had the level shifter circuit that uses a dual bss 138 and channel fat You know, even though I'm not using the secondary fat It's cheaper again to use the same component twice Even if you're not using the whole thing because you know one less bomb item is one less really you have to load in and uh, that you know should um Be able to power the the back light. So this should be uh, you know, basically pin shape everything can power everything You know, all the holes all the connectors are in the same spot But I just kind of like shifted things around To make room and I'm still using the same chips and then I had a little bit of space I actually had another hole even though this hole isn't for mounting this hole matches the lcd mounting hole This is actually just for testing when we do tests You know, I want to have it go onto a pogo pin bed It's really annoying to do that when there's only one hole if there's two holes Which is like I try to have always two at least mounting holes on every board Um, especially one this big that way it self aligns and then when you press it down onto the pogo pins Um, it's a lot easier. So this is just the I'll show on the overhead real fast what the board looks like and then we will uh We can go into the great search You ready? Yeah The great search brought to you by digikey and adafruit every single week lady To use the power of engineering to help you. Yes, you find the things that you need on digikey.com lady Ada, what is the great search of the week? Just a good question. Um, this week's great search is looking for a newer better Trim pot. Um, I'm revising this design the ice quartz lcd backpack Originally, I used um, the least expensive trim pot I could get which was is a perfectly fine trim pot But let's uh, look at how we can improve it. So let's go to the overhead and I'll show it off Um, so this is a board that connects onto an lcd and gives ice quartz the spi Interface and I have to revision for this anyways Ironically not because the chips the chips actually ended up coming back into stock Although the s s s t stop version is a little bit more available So I might still change this up for a t-stop depending on whether the so I see versions You know appear magically on digikey anytime soon Um, but I changed these two resistor packs now, you know changes connectors And then one of the things I really wanted to change was this little trimmer So there's a contrast adjustment for um character lcd displays You usually only have to you know trim them for the first time you get them Depending on your temperature and voltage power supply Um, and I use these little mini metal trim pots These are borns TC 3 3 x's which are extremely common, right? They're and they're very inexpensive and they're very easy to pick in place And they're very reliable Only thing is is that they're a little annoying like they're quite small and if you don't have exactly the right um You can't use phillips even though it looks like phillips you need to have a flat head So it's a little confusing to people because they get the wrong screwdriver Then they have the flat head and it has to be exactly the right side flat head. It's kind of hard to tell Um, what size it is. So I thought like maybe this would be a good opportunity if I'm going to revise the board To maybe pick a slightly better trim pot. I want something, you know durable Um about the same size. I have a little bit more space, you know, because I I did shift around some parts Um 10k trim pot, but I want it to be a little bit easier using the TC 3 3 x So, um, let's go to the computer All right, so this is the board and again here is the the trimmer. You see I have a little bit of space Right, it doesn't have to be as small As it is here. So let's go to Digi key and we will look for trim Potentiometer so the hardest part of this Is to search the spell potentiometer, right? Okay, so trimmer pots note that there's some wheel There's there's kits and stuff, but we want trimmer pots And a trim pots come again, you know, there's the through hole type. This is a through hole screw adjustable multi-turn um All sorts of stuff, but usually they don't have a knob where that's kind of how I would differentiate the trimmer versus a non-trimmer pot So first off the resistance. I do need to have it be 10 kilo ohms So might will just and it's the most common value. So let's just pick that off the top Number of turns only one turn. I don't need a high high precision You're gonna pay, you know, the it's one turn and then like Price goes up very high the moment you start doing multi-turns because it's mechanically more complicated It has to be wire round instead of just having a sheet of resistance material And of course, I want to only search for active um, and then Only surface mount because I want to be able to pick and place this component So it's really nice is that you can see most of these selections are already Kind of coming into play and I only have 76 options to pick from which is great Um, so if I search by, you know, just by price real simply Um, you will see the one that I use on the board right now the tc 33x again totally fine trim pot lovely trim pot love it, but it is a little bit A little bit challenging to use if it's the first time you've had to adjust a pot It's good for engineers not always very usable for beginners and makers or people who you know are not as um agile or have a full Full uh scooter over set Um But that said these are very close. So let's also look for only ones that are normally stocking Um, and I don't want to look at marketplace. I'm just gonna look at what's available from digikey Thankfully trim pots were not strongly affected by the chip shortage. So, you know, they do have a lot in stock Um, so there's a couple of good options So, you know, this is getting a lot closer to What I want, right? It's still a surface mount trim pot and so it can go through the oven and everything but it has like a very clear slot like it's very clear like it's a you need to use a flat head and You twist it and it's a little bit More compact. Um, this is kind of open frame. It's a little bit like whoa, like what's going on Um, and there's a few there's uh these ones also from uh borns I think yeah borns Um, these are like phillips compatible. Um, there's actually quite a few from nidek and borns um You know for my you know initial prototype I I ended up just going down with the 3 3 1 4 j because I happen to have some But um looking at it now I'll tell you actually why I'm thinking of changing So this is kind of the most common trim pot the 3 3 1 4 series But the thing about trim pots is that you know, they're it's a mechanical It's a mechanical interface much like um, you know, it's a normal fujo pot or terminal blocks and You really do want or usb ports you want to have some mechanical strength because it's not going through the pcb It's it's surface mount so it gives shear very easily And so what I what I actually liked was you know, I saw this one, but then this one I'm digging because Although they're both pretty good. This one goes underneath But this one I really liked that it had like these legs that stick out And I can get like really nice Chunky surface mount pads and I feel like that could give me a really good mechanical strength Um, that'll protect against shearing when you know because somebody like they twist they twist They maybe they they keep twisting a little bit too much. They could shear the pot off the pcb So I actually ended up And also another thing I like it has 85 000 pieces in stock. Can't argue with that Um, so the the night out night deck copal st4 et series Um, this is my pick for the great search. Just what I'm going to go Uh spec into my board. Um, it's also not too big It's only five millimeters by five millimeters Which uh is well within reason for you know fitting on that pcb. Do watch out the scale It's hard sometimes tell the scale. This can be you know 10 6 6 to 10 millimeters, but this one Is a nice size. I think it's mechanically stable and I think it's really clear Use a flat head and it looks like it would be very easy for people to use And that's a great search And that's our show for this week. Stay tuned this week on Ask an engineer for some surprises updates and more and that's all I'm gonna say So you'll have to tune in lady to say good night. Good night everybody. Bye. Bye