Two's Complement - Pictures and Candy with Arduino

Episode Date: April 26, 2021

Join our hosts as they talk about hobby hardware projects, past and present. Matt explains how he's building a digital picture frame out of a Raspberry Pi Pico and E-Ink display. Ben talks about building a Halloween candy dispenser using devices both serial and cereal. Matt and Ben discover they both liked MP3s in the early 00's.

I'm Matt Godbolt. And I'm Ben Rady. And this is Two's Compliment, a programming podcast. Hey, Ben. Hey, Matt. How are you doing? Great. Great to hear it.

So I know that one of the things that you do when you're not writing tests is build cool things. I try to. And you've shared with us at work a video of one of the coolest things I've ever seen, which is a... Tell us what you built. An automated candy dispenser. Why would you build such a thing? What on earth? What's the reason for such a thing?

Yeah, well, so I used to live in a neighborhood in Chicago. I still live in Chicago, but I live in a different neighborhood now. But I used to live in a neighborhood that was absolutely bonkers on Halloween. Is bonkers a word that you as an American would use, or are you saying it because you've hung around with me too long? No, I'm saying it because I'm looking at you and I'm like, what's the right word for it?

When I look at Matt, Matt Godbolt, I think bonkers. So no, it's because we, this, and it was like full size candy bars are like amateur hour in this neighborhood.

If that's all you're doing, you're just way behind the curve. And we knew this. And so putting a bowl of candy out is not only an unacceptable solution if you want to go trick-or-treating with your kids, which we did. Both my wife and I wanted to go trick-or-treating with our kids. And this is when they were younger and much cuter. And so, you know, we wanted to go out. And so, I can't just put a bowl of candy out there. What am I going to do? And I had been looking

for an excuse to use one of the many Arduinos that I had just ordered only to have them and just sort of assemble them and you know possess them collect them like i should put these things to use um and so i built two versions of it one version was a candy dispenser and this little like led backlit for some reason super mario themed um you know game the whole structure of it was like a carnival game i called it candy or death and it would alternate between two possible outcomes you hit there's a giant button hit the button and it like plays a song and it like alternates between these things candy or death like like the sort of the skill game on a fruit machine yeah stop it on the right okay yeah except it

you know there was no skill to it it just it just almost like a like a like a roulette wheel in a way oh okay so yeah exactly like that and then it would always land on candy and then it would dispense candy and the idea behind this right yes and more on that later um oh okay uh but the idea behind this is it was sort of like dinner and a show because i needed to have a hopper that would hold so much candy and i needed to know approximately even with the ridiculous traffic if there was like a line around the block of kids just hitting this button over and over and over again how long do i have out trick-or-treating with my kids before i have to go back and refill the candy hopper replenish right the hopper right got it exactly and so it would take a minimum of the first version i think

was like a minimum of like 50 seconds 55 seconds somewhere in there to just to go through the whole thing and then eventually dispense the candy and so and you know it wouldn't do it if it wouldn't do it if it was in the middle of doing it so you could just sit there and literally just hit the button over and over and over again and it would have at least like an hour to an hour and 15 minutes worth of candy so we can go to one piece of candy per minute yeah like even with someone just hammering the button a couple minutes worth of candy so we can go to one piece of candy per minute yeah like even with someone just hammering the button a couple of pieces of candy and you just know well i can get 120 150 pieces of candy into the dispenser i'm good for an hour yeah got it yeah

yeah yeah and it was the candy was kind of random and then that was sort of like i think part of the appeal is it almost always i had it i had it tweaked enough to where it would always give you at least some candy but sometimes you get a bunch of candy sometimes it'd just be a little and i thought that was just i i didn't want to fix that that wasn't a bug for me right this is all part of the entertainment right uh but yeah and so the first version was just sort of this backlit you know i basically like took some almost like i forget this paper but like almost like rice paper and i built like like a shadow box type thing with an led in the back and so it would sort of light up um and that was all controlled by the arduino and then the

second version was that plus i replaced the leds with a actual TV screen controlled by a Raspberry Pi that played an animation. And this had a skeleton hand that would spin around and music that would play. That's pretty serious an installation at that point, rather than a microcontroller and a couple of LEDs and a server. But we need to talk about how you actually built the thing because that to me is like the really interesting part yeah yeah yeah yeah it was cool um the so the candy dispenser itself ran on a arduino and the arduino had a uh stepper motor shield that you could put on it um all this is on my like all the code for this is on my public GitHub, by the way, which is BenRady. So github.com slash BenRady.

And it had this really cool stepper motor that I found and the Arduino shield that went with it. What is the stepper motor compared to a regular motor? What is the difference? Yeah, so it's basically just like a super powerful servo. So you can control with a regular servo usually, and also with a regular servo usually there's like a range of motion that you're limited to, right?

Sometimes they go, just keep going. But a servo is like a thing where I can pick what orientation I would like it to be pointing at between say like 0 and 45. Yeah, yeah. It's like a motor that you can basically just rotate as much or as little as you want and to specific locations, to specific okay that's it yeah right so like if you've got you know anybody that does anything in robotics there's a lot of servos going on right because you're just like i'm going to rotate this motor 15 degrees to the left and then whatever

it's attached to also hopefully hopefully does the motor know which way it's facing or i guess in your case it doesn't matter yeah in, in my case, it didn't matter. Basically, the thing that I figured out is I did a lot of testing with different kinds of candy. Testing, you said? Yeah. Always the testing with you. What is it? I mean, you know, you want things to work, you got to test them.

Maybe we'll call it experimentation. No, I like it. I like it i like it uh yeah the the so i had i had this like cereal dispenser that i had found that was like basically these rubber fan blades and the cereal would sit in a hopper on the top and you'd spin it and you've maybe seen this in cafeterias or in other places where it's just they fill right a big plastic hopper full of breakfast bowls yeah and then you just twist it two portions yeah and so i had one of those and i had hooked that up to not directly it was through a a little belt pulley system but i had hooked that up to the stepper motor um a to get more gearing so that it could you get a bit more torque, but also to elevate it up

so that it could fall down and still hit the right spot in the window where the candy came out. Got it. But I had hooked that up to the separate motor, and I figured out that you can't, if you just turn it in one direction, it tends to jam. And so what it would do is it would turn a little bit in one direction, and then it would back off and turn in the other direction, and then it would back off and turn in the other direction and then it would back off turn in the other direction and it would basically alternate back and forth to get out if there was anything that was yeah and so it wouldn't it was

much less likely to jam that way but then that also depended on the kind of candy so i tested lots of different kinds of candy and that's onerous testing oh man yes that. I'd be ordering these five-pound bags of candy off of Amazon, and I'd run it for like two hours and it would jam and be like, well, this is useless. I can't use this candy for anything. Except, you know, eating it all, which I

definitely did. At a certain point, I was like, maybe I should just do Tootsie Rolls because then I won't eat them. Yeah, but then neither does anybody else. Well, yeah, that's true. So point, I was like, maybe I should just do Tootsie Rolls because then I won't eat them. Yeah, but then neither does anybody else. Well, yeah, that's true. I did. So eventually, I wound up with Jolly Ranchers. Jolly Ranchers were a good combination of hard candy but with a wrapper that was flexible enough to where you wouldn't get this sort of like –

because I tried Starburst and Starburst would lock into position where the square blocks of the starburst would just like form a wedge and like no matter how hard you turned it it just wouldn't it's not gonna move right yeah i got it what an interesting thought yeah so like the little um tassels not the tassels like the plastic wrapper yes forms like a spring on either side right and also a force that tends to when if you've ever tried to squish and push it like twist it away so as they're kind of being squished together they move around a lot yep as opposed to as you say something like a starburst where essentially you're playing tetris except that the line does not disappear when you got it completed exactly yep yep that's exactly right so yeah so so after some some some

experimentation and testing with that um you know i had the stepper motor working i had the candy that i wanted to use and it was just you know sitting down and writing like a little arduino program to do this and i love the arduino ide it's super fun i was gonna say we should really talk about that because if if people i mean obviously there's physically building the stuff's cool and interesting we should definitely get back and talk a little bit more about how you actually put it together but the arduino programming experience is is pretty exciting and you should yeah tell us about it what all does it look like how does it how do you do this oh yeah i mean it's so fun to be able to just you know you could the id is really easy to use you just download it you plug in your arduino via usb

and you can you know run and you can run your you can upload your code to the Arduino super fast so you have a nice feedback cycle and you can just be plugging components into the thing if you've, I think the first one I did was one of the earlier models so I didn't have it on a breadboard

I just had basically just wires running out of the thing. I actually forget how those connected, if they were like little female connectors that you could put those wires into. But it was really easy to plug stuff into. So you could, you know, plug in LEDs, plug in like other, like the button, you know, I can control that. And you can, with a pretty fast turnaround time, experiment it right just try things out right and you know like writing in in what language are you writing all this well it's like it's sort of a weird c++ the arduino language right it's like you know not nearly as fully

featured but you have certain c++ language elements that are there um and it's you know it's if you've written any programming language it's not hard to figure out right and presumably this is we're talking like a page or two of code we're not talking like giant giant gobs of it not multiple files or are you i mean i don't know if my own like led Yeah, I didn't split it into multiple files. Actually, the most complicated thing that I did with the first version was... You know the Mario Brothers flagpole fanfare? Yeah. That was the sound that it played when it dispensed the candy.

And I had basically hand-coded that into the program as frequencies. Oh, yes. And I had found a couple of places where it's like I thought i had the frequencies right and i my wife is very musically inclined she played piano for years she played french horn she's a singer and i played it for the first time and she was like nah she recoiled in horror she's like that's that note is that's wrong that's just you're not you're off and i'm like if you say so, I can't tell the difference. But yeah, so that was, honestly, most of the code in that file was taken up by that, just playing that fanfare. And the rest of it was like, turn motor on.

Yeah, it was like, turn motor 180 degrees, wait two seconds. Turn the motor 180 degrees the other direction, wait two seconds. Got it. You know, flash the lights, you know, for the thing for the thing but that was all that stuff was pretty straightforward that's that's awesome and and so the feedback cycle is really really quick when it's like they're plugged in a usb board into your computer and then presumably you've got wires dangling out and you've got like a something constructed nearby with a stepper motor that's kind of at least just turning so you can see how it's going to fit together at least while you're developing it how do you take that

that's sort of connected to a pc and then make it run elsewhere it just seems like you know hey how do i install my software on it how do i deploy it right right well you screw it to a piece of wood that's the that's the main thing that you do is it persists does it once you've once you've copied the code onto that that little arduino you don't have to flash rammy type thing or that's just it you kind of deploy it and then you unplug it and then you turn it off and then put it somewhere else and turn it back on again and off it that's so cool yeah all you gotta do is turn it on it'll run so there's it's it's really simple and um you know it's not that hard to write a little while loop to listen for inputs and wait for the state of a button or a pin to go high and then do something. And so, you know, it's a really simple environment to work in and really rewarding, I think.

When something actually physically happens in the real world, there's definitely a warm feeling you get from, like, I'm controlling something in the real world yeah there's there's definitely a warm feeling you get from like i'm controlling something in the real world i mean it feels like magic my kids do some like lego mindstorm stuff and that's all like drag and drop things but that's it's still really cool to move a motor around and kind of go oh yeah that's that's that's a real thing that happened because you type some code in and but when you've actually built it yourself it's got to be even better yeah it was super fun so you've you've got this uh motor that's powering this uh serial dispenser and you've kind of worked out the correct sequence of wiggles and the right candy to put into it the right sweets to put into it for those listening in engb it's also a bit late to say this now but like for those who don't realize quite how big a deal halloween is over here in the states um yeah our international audience are like what are they talking about it's

like no it really is crazy you have you have to leave tons we leave like a big bowl outside we have the exact problem that you do which is that we come back and within like 30 seconds the bowl was empty because someone's just emptied the whole thing into their bag and i'm gone on and then it's like there's not really goodwill to your your uh the neighborhood kids if you if there isn't something for them so this is obviously a very real problem in a real world problem that you're solving with this uh this this uh approach but so anyway yeah you've built this thing it's all connected together do you put it outside and just do people steal it i mean that would be my concern in this kind of thing is that someone would go that that was also my concern i mean you know we live in a fine neighborhood but if you

give teenage kids access to a giant hopper full of candy they're gonna take it right it's the same problem as the ball so we had the fortune of um our house having a window directly onto the front porch right it's like kind of to the side of the front door and it was kind of a narrow window it was only about two feet wide and it had these child locks built into the window to where the window would only move up so far so that you could open the window and you know be safe with kids so they're not going to like little kids so they're not going to like push the window all the way open and fall out right Got it. And so I built it into that specific window with those child locks.

So the way it would work is there was a faceplate with the button and the speaker in it, and then that was on top of a piece of MDF that held the Arduino and the motor and the assembly for the hopper and all that stuff and all the you know power circuit you know all the power cables and all everything was just sort of screwed into that piece of mdf and so you could set it in the window and then close the window and lock it into place with the child locks i see and it would not only partially closed but yeah open it anymore

after that right right it was the faceplate was the exact height of the gap that was created by I see. robbing the candy because yes you're just breaking into my house actually breaking and entering sort of outside of the spirit of halloween yeah yeah even over here yeah um so yeah and then the cool thing is i could pull the shade down behind the window so that i would prevent any light from sort of leaking through because again it's like i want it to be dark on the front porch and i want the light from the candy dispenser to be the only thing you really see right ghoulish illuminated by the flashing red and green yeah candy or death right or the screen you know in the second version in the second one yeah so we should so you when i mentioned death before you said there was a story is this the right time to tell that story yeah so so the thing was is that you know my my wife and i it's not like we had another supply of halloween candy right so when we came back from dispensing or when we came back from going trick-or-treating we would go in

our house i just leave the candy dispenser there and this was great because you get to hear the reactions from the people we'd be just sitting in our living room so cool yeah and people would come up and you'd get to hear their reactions and And by far, the thing that we heard most often was kids being disappointed that it didn't land on death. Right? They'd just be like, so they'd just do it over and over again. And they'd be like chanting death, death, death, death, death, death. And it would land on a kid and they'd go, oh, fine. What is wrong with children these days?

Yeah. Yeah. So I don't know. so they went to death did you ever were you ever tempted to to meet out you know like one in a hundred deaths something like that i did have the idea i did have the idea of having it look like it like glitched out and then switch to death and then throw like a jump scare picture up on the screen you know something that's not too terrifying but something from like a horror movie that would just you know the deserves like pop up on the screen and scare you and what i wanted to do was put a webcam over the thing so as soon as it did that it would take a picture and then post it to a twitter account and then i could have the candy

or death twitter account with people going like you know know. About five minutes before someone pointed out you probably shouldn't be doing that without consent and all those boring but very important things. Again, Halloween. Actually, you know, it's funny because like... All bets are off, right? You waived your rights when you walked up my front steps. Disclaimer at the foot of the stairs.

It wouldn't be the craziest thing that has happened in the neighborhood on Halloween, for sure. Not even by a long shot. There's pretty macabre things around here. I've seen, like, bodies on spikes in the front garden. I'm like, this is not... That's not cool. Yeah.

But, yeah, so... But I never did that. In fact, I don't own it anymore, because when we sold our house, that was part of the deal for the house. Oh, my gosh. I sold it with the house, because it fits that one window. It house that was part of the deal for the house i oh my gosh i sold it with the house because it fits that one window it's that window of course rebuild it to do and we don't even have a window in our new house that it would that it would be you don't have a window for this oh you don't do that it wouldn't be i was gonna say you just gave it a brick brick cube i live we're done with looking it people. It's actually all window. I live in a giant glass cube. It's like an Apple store.

Right. I mean, from the webcam, since you've moved, I haven't seen a new house. Like there may well be no, no windows. I can't see any windows.

So I assume it would make sense. There's not, there's no windows here, but no, we couldn't have used it. You sold it with your, your, your,

your house because it doesn't fit the new house. And did you leave them with like an owner's manual? I made them an instructional video, actually. That's so cool. Yes. And actually the presentation. So you've seen my presentation that I did. I have, which is what clued me into knowing about it.

Yeah. I left that. The reason I did it is because I was selling the house and I was like, oh, I'm not going to have this anymore. And also the new owners need to know how to use it. So I'm going to do a talk on it and then I'm going to leave them the link to that talk and some video so they can see some other things. So is there a YouTube link

actually in the closing documents for your house? That would be the legal documentation that says... Sign the rights of the video over to them as well. be the legal documentation that says yes sign the rights of the video over to them as well the seller represents that this is how the candy dispenser works

and yeah it's part of the inspector was like this this candy dispenser is not up to code there's yeah did you show him the tests did you write any tests uh did i

write tests so i in the arduino ide i had a test mode right so if you um turn the thing off and turned it on and you held down the button and this made me think when i was making this is like surely surely surely there are like old school coin-op video games and vending machines and things where if you turn the thing off and you enter in the right code in the vending machine all the candy comes out. All the food in the vending machine comes out.

That has to exist. And doing this sort of reinforced that for me. If you turned it off and then turned it back on and you held down the button so that the button was pushed when it started up it would run a diagnostic. And it was basically just me with a bunch of asserts checking a couple of the functions that I had written.

And then it would go into this like auto dispensing loop that I could use for stress testing, right? So if I was testing out a new kind of candy, I could just do this and leave it for three hours or two hours or whatever and come back. And if it had jammed, then okay, that candy was no good. That's, and come back and if it had jammed then okay that candy was no good that's do you get uh feedback if it does jam is there like a readout from the motor that says no it doesn't it's gonna be a fire soon because the motor oh okay yeah clicking horrible

thing actually what would happen is the belt would slip the motor was powerful enough but the the teeth on the on the timing belt would just slip got it yeah and so we haven't talked about the second version very much so that was more complicated than just an arduino and some lights and and a and a while it had um it had a raspberry pi did he say and a screen tv yeah yeah so the way i did this yeah tell us Tell us. The way I did this was I hooked up a Raspberry Pi to the Arduino over the same USB cable that you use to program it. Right. And you can just, you know, talk over that serial connection and send bytes in both directions. Right. Yeah. And then on the Raspberry Pi side, I just, you know, opened up a serial connection to that device and read the bytes that it was sending.

And all I really needed was just the signal for when to play the animation. So I don't know what message I sent. It was probably just some like hello world string or whatever. So the Arduino was the driver, driver effectively it was in control of the whole show here and it was using the raspberry pi a full unix operating system on a small arm many hundreds of megahertz arm chip as essentially a glorified graphics card yes on a wire yes that's exactly right that's exactly right and so when it got the signal it would play it would play the animation i actually did it all in chrome with svg so it was like serving up a the the thing running on the raspberry pi was

listening to the serial port and serving up a uh very very tiny web app that would play this animation and play the music right um and it would just do that in response to getting the signal over the so it was a dynamic web page that was showing the content yeah used that is i mean if we people talk about being a full stack developer but until until you you were writing an arduino like low level um stepper motor driver talking over serial to a web browser and that's a whole product that then you're not full stack yeah right right i don't know gatekeep what full stack is not at all you know like it's it's that's just amazing to sort of have a fun project that touches so many different areas of problem solving and computing. Yeah. And yeah, it's like it's like that when you type something in your web browser, what happens when you push the button on this thing?

What happens? Well, first, the Arduino sees that the pin has gone high. Then it starts playing a song. Did you use I'm going to have to bring up my favorite thing to talk about, which is, you know, when you're down at the low levels like this, First, the Arduino sees that the pin has gone high. Then it starts playing a song. I'm going to have to bring up my favorite thing to talk about, which is when you're down at the low levels like this and you're looking for edge events like a button being pressed. You mentioned earlier you had a while loop, but did you use an interrupt?

Tell me you used an interrupt and you just went to low power mode. Oh, it's so disappointing. You missed a golden opportunity. Can you even do that on an Arduino? Yeah. It's so disappointing. You missed a golden opportunity. Can you even do that on an Arduino? Yeah. Yeah. There's some of the sort of like pigeon C++ extension-y type things that they've got allow you to tag stuff as interrupt handlers and set them as interrupt handlers and stuff.

So you can do some of that nonsense. Did not know that. You didn't need to do it, so you didn't. Because it turns out that if you're not battery constrained or anything like that, sitting in a tight loop going, while read this memory address is not equal to zero, sitting in a tight loop going while read this memory address is not equal to zero sit in a tight loop works just fine it's just fine yeah but no i just an opportunity to kind of get that end as well as a few just another rung down yeah well yeah if i was running this thing off a battery that would have been a whole other deal. For sure. A whole other world of consideration. So the obvious next question is, what are you going to do in your new house?

What am I going to do in the new house? You know, the thing I built in my new house is I built a golf simulator. Because I like to play golf. Oh, well, this has taken an unexpected turn. But that's almost like a whole show unto itself because man, once you have simulator data that you can export and analyze

there's a whole other level of nerdery that happens. Oh my gosh. That is definitely a whole other episode. That's another talk. Okay. You definitely piqued my interest there. I'd love to hear about what the heck that is oh my gosh yeah that's that is definitely a whole other episode that's another talk okay yeah all right but you definitely piqued my interest there i'd love to hear about what the heck that is but no no plans then for any halloween magic or for resurrecting something similar to it is that you've kind of done that you've got the t-shirt the kids are more grown

up now baby yeah our kids like you know they don't you're allowed out of the house at all obviously yeah right when when there isn't a pandemic going uh yeah they they can go trick-or-treating by themselves now honestly if they want to and i think they did last year or the year before it was snowing i remember but yeah it's it's sort of been there done that you've you've you've got the t-shirt you've had your fun and now you've moved on to more things that actually impact you directly. I know how much golf means to you. So a golf simulator is more in keeping with stuff that you're interested in rather than just service to the neighborhood kids.

Yeah. Cool. Well, I guess we'll talk about that another time. And I'm disappointed that you didn't have an actual test framework for this and you just have to hold down a button. I did write tests for the web app that lived on the Raspberry Pi. That had tests. Okay.

But the Arduino code only had the diagnostic mode. Although, in fairness, writing tests for web pages is about as difficult as writing tests for embedded systems, right? It's still awkward to do it most of the time. It's much easier. Is it? Oh, it's so much easier. We should not go back to testing just yet.

But at some point, you're going to have to explain to me how to write decent web tests because I can't. But yeah, that's another topic. That's another topic. Yeah. Do you want to talk a little bit about your picture frame that you've been working on? Oh, I guess we could. I would like to hear a little bit about your picture frame that you've been working on? Oh, I guess we could.

I would like to hear a little bit more about that. So, yeah, I saw a YouTube video from an acquaintance of mine who had made a kind of joke present for his mom where he built a picture frame into uh with with an e-ink paper uh into a into like a little uh photo frame like a regular photo frame that you'd put a normal photo in and gave it to his mum as a present but unbeknownst to her every day or every couple of days the picture would change overnight and he was he was betting how long it would take her to notice and unfortunately i think she realized something was up because it didn't look quite right and you know it was

she knows her son so it was it was it was under intense scrutiny but anyway it was inspirational to me and i thought i've just been lucky enough to be sent a raspberry pi uh zero which is a raspberry pi that doesn't run unix, unlike all the other ones. It's just a chip on a board and a very low power chip at that. And I thought, hey, why don't I give this a go? And I'm going to try and make it run off a battery because Charles's setup was on an Arduino,

which I've also got an Arduino knocking around somewhere as well. They're great fun. The IDE is just brilliant, like we were saying before. I was just interested in using the raspberry pi uh sorry pico if i said zero before i meant pico i forgot what i said it's late in the day now but yeah raspberry pi pico it's just nothing to it just a little board and so um i picked up the same e-ink screen and this is a color e-ink screen so it's got seven colors which is a weird number of colors to have as you can probably imagine eight would make more sense and so it's

four bits per pixel bizarrely the internals of this screen are very much like an actual crt display like it has you have to set up timings and uh how many pixels across it is how many pixels down it is how quickly the vertical refresh happens. But it's clearly not updating 60 times a second or 50 times a second, right? That seems to be the communication between the RAM on the board and the actual physical screen itself. This is a well-established way of addressing each pixel. The best way of doing it is to sort of stream out the colors one after another

to some circuitry that can then make sure the right color gets to the right pixel. That said, though, the way that it works is that you kind of populate this memory and then you kind of say go. And then it starts doing the kind of Kindle thing, if you know what I mean. If you've got a Kindle that's got an E-ink display, it kind of flashes on and off and kind of has a real laborious time of it as it's kind of like reset the e-ink except it takes even longer because it's got multiple color cells to do it and it seems to be there are just different cells with like colored lenticles over the top of them to give you this the seven different colors and the seven colors like red green blue yellow brownie orange uh that's five um there's another but to be honest most of them look brownish right it's not very good and so you and it's 600 by 448 so it's it's quite

high resolution so some dithering gets you some way but all the algorithms i've looked at for dithering the standard ones um floyd steinberg error diffusion is the one that i picked um they they work really well with luminance from a screen but they don't seem to work as well with essentially a paper medium which is essentially subtractive and i'm trying to wonder if there's some almost like newspaper style half toning that used to happen you know like on printers versus the kind of thing you do for a screen that i might look at but anyway the the code it runs on the little um zero it talks over spi which is a standard serial protocol to the the display i've got a little

sense uh direction sensor on there as well which tell can tell whether it's up. Oh, that's neat. So that, yeah, if you can pick up the picture frame and put it on its side, it'll only show portrait things and you put it back in to show landscape photos. And so there I use an interrupt handler. So I can go into low power mode. You see, I get it out in the end.

We're talking about interrupts. So that it can go into low power mode between essentially what would be a sleep for, at the moment I've got it like five minutes, just because can see it see it go uh it's been a lot of fun um i plan on putting the whole thing at the moment it's on my shelf in the other room but it's like if you to look at it any further than um sorry any closer than like a couple of feet you'll notice that behind it is a ton of breadboard and wires and batteries and things so it's not very good i'm i'd like to get it to the stage where um i can get a like a breadboard an actual um you know copper track breadboard old school not like the pushy pin

ones but and solder onto it and get that um actually sort of fabbed enough to then get everything into the little clip frame that i've got for it. Because the whole thing is only like, you know, a half a centimeter thick, which is, I don't know, some 29 64ths of an inch or something. I don't know. Americans do a crazy set. But yeah, five mil kind of thick thing. But it's been an interesting experience. The Raspberry Pi SDK, the Pico SDK, the it's been an interesting um experience the the raspberry pi sdk the the zero sorry i keep

saying zero the pico sdk is shipped as like a github project that you just get clone and then you kind of just c make it in and it's all written in c and c plus plus they've done a really good of documenting it the you kind of link the whole operating system such as it is it's just support libraries into your executable and because it's you you have like a sibling directory with all the code and it builds it as source so you change your compiler and it's going to pick up all the the whole operating system and you just get like a dot a single image to deploy to the the app to the device and the way you deploy is when you turn it on just like you were describing before there is one button on the top of the thing if you hold down that button when you're

when it's powered on it goes into like a receive mode yeah and there it looks like it's a usb thumb drive oh neat and you copy a single file onto it and as soon as you finish copying that single file into it that's the image it's going to run from then on it just flashes that image and now it's that so i've got like a little watch loop you know we've talked about the uh the watch sort of targets before now which look for the usb drive to appear and when it does it copies the current version and then it waits for it and then it gets the serial port debug interface up and just waits on so i've got a little like repl style thing where i can just hit build the only annoying thing is i have to like press the button and until i wired in a reset button myself as well it meant that i actually had to unplug and plug the whole thing back in

again which was a pain in the proverbials but um you can get an actual debug header for it and then actually debug it but the easiest and best way to connect to the little three pin debug uh system that it has is to use another raspberry pi zero as like the adapter and these things are $3.99 each it's just silly so i just ordered 20 of them because i'm gonna find you this is exactly like you and your arduinoinos on the shelves. That's why I have half a dozen BBC micro boards sitting on my shelf, right? Exactly right. So yeah, these cool things are, you use them as the adapter, the debug adapter. And so unfortunately, because everyone has rushed off to buy them, they're out of stock everywhere.

So I'm waiting for more to come through, which is why I've sort of shelved it for now until I can i can uh debug it properly and and get my few other bits and pieces through but it's just great fun it's great fun to have something uh and i'm hoping that it's inspirational for the kids to see that with relatively straightforward code i mean again at the moment everything that i've done in my code with the exception of the gzip library which i've kind of got hidden away somewhere else to compress the images and put them on uh into the like the image itself everything fits into a single screen yeah or so and that included me me going slightly crazy and um wrapping the screen driver that i had written in a nice c++ 17 objects that are all you know all the nice things all the nice trimmings so which means it's more than one page of code it's one file i said it was one screen i mean it's one file it's about two screens worth of code in as much as a screen is a decent

measurement of code but it's not much it's just fun and exactly as you say like hey when you when you are just doing a relatively straightforward symbol thing, you don't need very much code. Like while, you know, I go, hey, sleep in low power mode for five minutes. Cool. All right. Now send this byte over the SPI to the display driver, which wakes it back up again from its slumber that I put it in. And now stream 600 times 448 divided by two, because that's four bits per pixel, colors from an array that I just g-unzipped. Okay.

And then let's sleep again for a bit. You know, give it the magic command to say and go. And now watch it do its screen changing. And now I'm going back to sleep again. But it's so cool. It's so cool. If you don't mind a very dull, slightly brown image of anything you wanted to put on it. So my original hope was

to give this to my wife as a valentine's present oh yeah and uh i failed to deliver to her in time next year next valentine but i but i told her about it and so i got almost as many kind of reward point romance reward points for uh for the idea of it than the actual implementation because i don't know how excited she would be really about a muddy picture of pictures of us they say that it is the thought that counts they do say that it's the thought that counts and this is also uh not the first time that she's had to put up with devices that i've wanted to make as either gifts for for her or for me because i think for my 30th birthday i said to her rather than getting anything i was gonna getting her getting me anything i should say i was gonna

buy a bunch of components and build my own mp3 playing system that could plug into my amp i still have the parts this well 40 15 years ago i got it working but ultimately i ended up buying like a squeeze box which was this commercial offering that did the same thing you know this is like pre sonos pre yeah um that kind of stuff where i you know i had a server that was chock full of all my mp3s and i couldn't play it on my nice hi-fi because there wasn't a way of connecting the two and so i thought well i'll make one do you do you see i don't know if you can see this in the webcam you see the sort of steel and plastic contraptions sitting on the top of my on the top shelf i have many times wanted to ask you what that is that is a computer that i installed into my honda civic in around 2002

to play mp3s because you couldn't buy an mp3 player at the time and so that one is voice controlled there's a little lapel mic that i wired through the car up to the driver's seat and there was a push to talk button and you would push it and i it would use the windows uh voice to text api we should talk sometime about the trials of trying to get a computer to shut down reliably and not overheat in texas in a car in a car if it's a windows machine um but wow but you could push a button and you could say the name of a song album or playlist and it would play that song album or playlist that's amazing oh my god that's so cool you uh when was that i mean obviously this was when you were in Texas.

It was immediately after I graduated school, and I'm like, I have money. I can spend this money on whatever I want. I'm going to build a computer into my car, right? That's so cool. That was my geek project. Oh, my God. MP3 players, man. I mean, as if we needed more reasons to say that we are similar. We've taken, we took a different fork at the beginning,

but we have remarkably consistently done similar things about 15 years ago. MP3s. That's cool. Well, there's lots more to talk about there. And yeah, I definitely want to hear your your golf machine at some point and maybe we should record something and put it on a you know a youtube for people when we talk about that we can do that then we can critique your golf swing as well oh boy critique golf that'd be another that's embarrassing yeah you know we could do maybe we should do like a youtube channel something and do some of these

you know we're talking about these presentations that we're given but we've given before we should probably we could at least collect them in a playlist we've got a few things that we've talked about that might be a good idea cool my friend yeah well let's think about that some more when we're not recording for a podcast so we can actually talk about it yeah good call sort of make ourselves promises that we won't be able to keep. Right. And we've got tons more to talk about. So I guess until next time. Yeah.

Sounds good. All right, mate. Laters. Later. You've been listening to Two's Compliment, a programming podcast by Ben Rady and Matt Godwald. Find the show transcript and notes at twoscompliment.org. Contact us on Twitter at twoscp. That's at T-W-O-S-C-P.

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