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the Ben Heck show is brought to you by element14 the electronic design community where you can connect and collaborate with top engineers from around the world join now at element14.com amazing hacks how can we make this portable inspire designs I am the internet troll regrettable acting each week element 14s the Ben Heck show brings you innovative projects using electronics engineering and more this is the Raspberry Pi computer it takes the main components of the Raspberry Pi and boils it down into one simple circuit there's a Broadcom chip and a flash memory to use instead of the SD card then we have an i/o board for it which allows you to do testing and troubleshooting now felix is working on an idea here to turn the Raspberry Pi computer into a custom graphing calculator yeah so for the screen I want to put on an Adafruit TFT uh-huh and and kind of mimic the button layout oh yeah let's say you get a matrix hooked up here and there's plenty of i/o on the compute module actually a lot more than the standard Raspberry Pi has so we can make whatever kind of matrix as we want yeah so I just got the minimum number of pins connected to the screen which is seven and then power and ground and then it made it three by four button matrix and just to test it out to see that we the idea would function so the idea is to boil this all down into a single PCB that looks like this yep all right let's design it send away for it and see what happens all right so this is how I design the Raspberry Pi computer module calculator board first thing I did was go over to element 14 and found the design documentation they released the whole schematic for the i/o board and the carrier board and then I also downloaded the Eagle library and then I imported that into Eagle so I can get the footprint for the sodium socket I put that into my design and then I put in all the support circuitry and then also added the TFT screen and then laid out a keypad matrix then I went over to the board layout and I made a form factor of about seven well it is 7 by 3 inches and I put the TFT screen the support circuitry and the sodium socket on here so I'm going to take a look at the TFT part I'm going to right click open package and see here is where the ZIF socket connects now you see here the stop mass has to be checked in order for the solder mask to not be on top of the pad now this may be a problem later in the episode but I'm going to send this off to Oshkosh and we'll be here in three to four weeks Felix Felix I think this is the board from Ocean Park oh great yes all right all right so we got our board in from Ocean Park it looks really great I'm just gonna look it over to see that everything is gonna work out we'll put our sodium saket right here that looks like it'll fit that'll be nice all of our buttons here our button matrix on the front buttons fit let's see if the diodes the pads for the dials are a little big but they'll work we have our our header for the power everything seems to be okay except for it looks like the solder mask the stop mask wasn't checked them apart so we still have solder mask on where the ZIF socket is supposed to go so we might need to do some kind of rework to fix that what's wrong Felix you look sad but then I made some mistakes on this board oh no the stop mask wasn't checked on this part here for the ZIF socket so we can't connect the screen then right can you try to scrape off the solder mask so we can get at the pins yeah I tried scraping it off and I tried sanding it but I get shorts whenever I solder onto it oh it's too fine pitched and really reworked by hand yeah that's too bad made some miss connections here on the Soudan socket as well oh and this is probably also a little too difficult to rework oh well the clock's ticking on this project what if we use the keyboard matrix part of it and chop off the top so this part we can wire manually using a screen and a Raspberry Pi A+ will keep the matrix and hack that in hey yeah that could work let's check out the whiteboard here's the hack we came up with to get this project to work will keep most of the board specifically the PCB matrix that has all the buttons on it but will chop off the top that had the compute modulo attachment and the LCD attachment we'll replace that with a Raspberry Pi A+ module which is pretty small form-factor it's no wider than the board that we had and then we'll hack down an Adafruit LCD to plug directly into that it won't be as compact as before but we can make it pretty close we'll have a pair of lithium ion or lithium polymer batteries behind the keyboard a charge regulator and controller behind the Raspberry Pi and we'll make some rubber keys using the formlabs SLA printer for high detail then we will 3d print a front and back of a case probably with PLA so doesn't work and will sandwich all the components between it so you know kind of taking the long way around the barn to get this to work but the end product should be pretty close to the original intention here is our test rig for the reworked calculator we have a Raspberry Pi B+ with the expanded header an Adafruit screen connected to that and the hacked up keyboard matrix that we talked about now we have all these components working the keyboard matrix is sending characters to the i/o stream so it can act as an actual keyboard and Linux there's even a joystick control so what I'm going to do is break this down even further so we can use it with a plus module and make something that's pretty much the same size and form factor as what we originally intended actually to be pretty close so that's what I'm really good at is fine soldering work so here I go we have the switch matrix working but there's a problem with the joystick yeah we've got a four-way switch and we have only three GPIO left that's kind of tricky so there's a switch that has a common pol ug put that to ground then you'd see which one of these are pulled low and then you know its direction you're going in we have no other GPIO we can use nope what if we set up like a 4-1 matrix I know that sounds kind of confusing but like if we had four states reach of the switches and then we see which one of those go to ground like this so you'd use one of the GPIO as an input here and do an internal pull-up on the PI so it's normal status you know high one and then to control this what if we did something like used a multiplexer you use those in school yeah okay so you can do this we can use a well we don't have any two to four but we have three to eight so we can just use a multiplexer can take a small number of inputs and turn it into a higher number of outputs two to four multiplexer like this one you would either input 0 0 1 1 0 or 1 1 so 0 1 2 3 and those could be your states that you're looking at and these numbers in sequence will make either this low this low this low or this low and when not active they'll be high so this is what your truth table would look like and it's starting to make sense yeah so 1 2 GPIO 3 and then we connect each one of these this will be up-down left-right so in your main matrix sequence you could say okay if this is 0 and this is 0 then we know that we're pushed up else if this is 1 on sequence 0 then we know up is not pressed so you go through a 0 through 3 4 sets and then you can figure out which way the joystick is going yeah we're using the original keyboard matrix that Felix designed for the compute module version of this product we've chopped off the top of the PCB where the compute module is going to go and place our Raspberry Pi A+ in its place we're attaching the keyboard matrix wire by a wire directly to the GPIO making sure that we don't lay wires over pads that we might need later so it's more about wiring things in the most convenient way rather than the most logical way we're also attaching a 3 to 8 multiplexer which will allow us to use the joystick with only 3 io remaining finally we attach the LCD screen by placing it inside of a frame that will snap over the Raspberry Pi plus to keep the alignment correct and using thin wires to the data signals and slightly thicker wires for the power and ground felix has appended his matrix code to include code to run the multiplexer so here's what we did we took the column count which goes from zero-to-four that normally drives the columns and we're putting it into two bits of GPIO so basically it's going to be 0 0 0 1 1 0 1 1 obviously there's another state which would be the number 4 which would be 1 0 0 but we're not going to actually use that so what it does is it puts that onto the multiplexer line and that will put the multiplexer in one of four states this will be low low low low and whichever state is an active will be high so it's an active low state so after we set the multiplexer we then read this GPIO so if the multiplexer is in a certain state and the GPIO is pulled low then we know that direction has been pressed and then so I'm highlighting the things that output to the multiplexer I'm highlighting the thing that reads the multiplexer and then this is what determines the switch that you pressed so yeah basically our three i/o to i/o drive a 2 to 4 multiplexer to analyze the four states of the d-pad and the third remaining i/o the very last one and the PI reads the output of this alright now that we've got code written for the d-pad I'm going to compile it and see how well it works so I'll SSH into the PI here which is this right there and then I wrote a little script that will rsync the source directory on my machine with the Raspberry Pi compile it and then automatically start it alright so now it's our syncing which synchronizes the source directories and then it compiles and once it's done compiling it'll start the program ok now it's running you'll see it pro you don't see it running because it runs in the background so the code is compiled and in a program is running in the background we can test the d-pad let's see here up down left right cool it's exactly what we wanted to do it's time for a tech timeout fly-in dispensed formlabs was kind enough to send us a form one printer to use this summer on the Ben Heck show this is a UV resin printer and it uses a laser to cure resin one layer at a time to 3d print objects the advantage is you get a lot more detail than with a fused deposition modeling printer such as a MakerBot or anything else that uses filament let's unbox it it's just kind of laying on a bed of plastic oh it's pretty heavy look at that the coloration of this shield here is to prevent natural UV light from the Sun or other sources from curing it resin ahead of time and what I believe they do is they have a laser down here at the bottom which has a galvanometer which is a thing that basically moves at high speed and then aims a laser to paint the layers so you don't move the laser you reflect the beam in different ways because you could obviously move a mirror faster than you can move a laser but can you dodge a ball hey I wonder if we could use this to create a renewable energy source and doc ock arms or something does this remove it must slide out otherwise they wouldn't put tape around it and that's how I ruined it there it goes so the laser looks like it's back here hits a 45-degree mirror and then hits the bottom of the resin tank so what it does is it prints one layer at a time and this main arm moves up and this is basically just a typical z-axis the printing surface must be in a different box that would click in right here move with this arm okay I think I'm going to put this in position over by my 3d printer and hopefully we'll print with it soon here's the parts we have so far Raspberry Pi A+ multiplexer at our directional pad our keyboard matrix I put the LCD in its own custom frame and the frame folds over tabs into the A+ mounting holes alright so we still need the battery pack so what I'm going to do is flip this over and figure out where I put the batteries I've already started printing the front half of the case but we won't know about the back half until we know how thick the battery packs will be so we're going to go with two packs which will give us seven point four volts which will knock down to five volts then Felix created this charging circuit it's a variation on ones we've used before it's going to figure out the best place to put everything and then we'll solder it up and design the rest of the case alright I'm going to wire everything up in this position and then we'll see if it still works we exported a DXF from Felix's PCB file into Adobe Illustrator and this gave us the position of all the buttons for the keypad matrix above this we created a copy of both the PCB in its chopped-off form and the buttons around the buttons we created a slightly larger layer which will be the gap around the buttons the hole that they fit in there's also going to be a four-way circular joystick right here so I usually do point 0 to gap around buttons it's a little much but it's a it always works we've also drawn in the raspberry pi the case n the LCD here's a side view of everything goes together I use purple for the ocearch PCB and these are the tax switches and there are going to be buttons on the tax switches for the buttons we're going to use the formlabs form 1 SL a resin printer it uses a laser to actually cure resin one layer at a time so we can get 3d prints with a much higher resolution than we can with the MakerBot or any other fused deposition modeling printer yeah so we can get some nice intricate text on the buttons such as the numbers or symbols so we'll probably start that first and then we'll start printing the large portions of the case on the good old MakerBot so to marriage in 3d printer heaven so the case will have a rear portion a main portion and then a raised portion that holds the screen they'll also be a 1/16 inch thick laser-cut plastic piece and this will have all the detail on it like this our plan is to make this you can use it in two orientations portrait use it as a calculator but then if you turn it sideways the button mappings change and it becomes a QWERTY keyboard as seen here so much like our Sinclair spectrum project every key has like ten functions once we get the basic layout done we went into Autodesk one to 3d and started making three-dimensional buttons yeah so we'll get really fine detail using the formlabs printer so it should be neat alright we'll get all the buttons printed get the case printed and then start putting it together I'm going to do a test fitting so this plate goes here and then this will sit on top of it this black piece will eventually have text on it but for right now it's just a temporary assembly let's put a few rows of buttons in oh good they fit I mean I had no doubt they would fit I never had a doubt in my mind Joystiq probably didn't need to be that high but oh well ok looks like all the pieces are coming together so we have the frame around the LCD since it's a little taller than everything else a spacer frame which will have the key sub-functions edged into it by the laser lunch people once we've designed that and we have that and then we have our formlabs keys that we made yeah so far so good here's the front of the case with all the buttons in place I'm going to lay the calculator into it and it'll just press fit into the front well it's supposed to if everything lines up I also have the back of the case it just got off the printer does some cavities for the batteries in the charge circuit I'm going to put the two three point seven volt lithium-ion battery packs in the unit I'm going to wire them in series to make a seven point four volt battery they'll be controlled by this charge controller which will be connected to this charge jack and then we have a power switch which sends the seven point four volts to the five volt regulator turning on the Raspberry Pi I've connected the power switch to the five volt regulator 500 regulator to the PI the charge circuit to the battery and the last connection I'm making is the positive voltage coming from battery I always do this last to avoid short circuits and other problems because this is a live connection I'm wiring and here we go all right it should have the ability to turn on I guess let's give it a shot I don't even know if it's gonna work probably will though I mean we're obviously experts of dangerous screen lit up nothing smoking yet oh there we go yeah it's booting okay I'm gonna give this back to Felix so he can finish his keyboard code Felix burnt the midnight oil this weekend and got the code working for the calculator thanks Felix yeah he can fix it all right so we execute the simple calculator program and then this X is the directional pad right up down left right yeah sweet okay Oh welcome to calculator C calculator all right let's try some addition enter the number of elements you want to add well obviously we have to add 14 elements together okay eight plus nine plus six plus then I'm just going to keep going until it stops me how long chain these numbers B I don't know exactly are the integers yes okay so 32-bit processor probably up to 2 billion 2.1 billion let's try let's go to 0-0 zero zero zero zero zero zero and five one yeah yeah that's right okay I'm gonna try to break it okay I'm gonna try to do addition to the number of elements you want to add - lets add okay one and let's add negative number two have you checked this yet oh there we go negative nine okay so it is an integer all right let's try some more operations let's try division so you know of course I'm gonna try to divide by zero divided by zero oh sorry really it had to be done yeah okay well that worked out pretty well Felix and then we have a switch in the back to enable/disable the Wi-Fi module because it takes a lot of power yeah all right so there you have it the Raspberry Pi calculator and it works like this with the QWERTY keyboard and like this as a keyboard oh can you show us how to boot into the other mode made a function for that right yeah um hold on this shift key mm-hmm and then there's these two buttons here mm-hmm so give a little message and then it'll begin hey and now it booted up in this orientation so I can use it like a computer suite so I always like the pocket calculators and computers in the in the 80s so this is kind of a fun throwback to that the challenge for this episode was to build a custom graphing calculator using a Raspberry Pi we started out with the compute module but had some issues with our custom circuit board so we switched over to the Raspberry Pi A+ we created a custom keyboard matrix that had both landscape and portrait variations you could hold it in two different ways and Felix wrote code to provide the calculator functions in the end we managed to build a custom calculator and learn about a new way to create 3d printed objects using the new formlabs SLA printer for this project what would you have done differently have you ever hacked a graphing calculator before let us know in the element14 community where you can also keep track of upcoming events builds and episodes we'll see you next time oh yeah okay it's your job not to laugh max up oh no the birds are attacking there's based I forego person I think you got stabbed or shot or some foul play happened it's too good yeah Coco yeah I don't know exactly what happened but I believe he's dead the Ben Heck show is brought to you by element14 the electronic design community where you can connect and collaborate with top engineers from around the world join now at element14.com