the Ben Heck show is brought to you by element 14 the electronic design community and online store built for engineers and hobbyists alike join now and browse the store at element14.com hello and welcome back to the Ben Heck show over the years have made many videogame consoles and old computers into portable versions of themselves one I’ve never gotten a crack at until now is a ZX Spectrum this is kind of hard to find in America since this is mostly a UK Europe computer so we’re going to take it apart and see what we can do with it but we have to be careful because this is the only one we have let’s get started amazing builds exclusive mods cutting-edge ideas electronics engineering and more every week on element14 the Ben Heck show I only have one ZX spectrum so I don’t want to break it therefore we’re going to do this project in several steps so I have the time to do it right the overarching build is to take it apart modify and compact it add modern storage such as an SD card at the debye cassette tape make a new keyboard and of course find a way to get a better display out of it then we will try to make it into a compact laptop or a handheld form factor so in today’s episode we’re going to take the unit apart examine the components try to get it running off of a modern voltage see if we can get a video display from it and replace whatever components we can to start with here it is this in Clair ZX Spectrum or as they say in other countries ZX spectrum not sure why so this was the whole computer although you would need a tape drive to go into it to get your programs there’s often an expansion bus which is used quite a bit there isn’t even a power switch on this thing so the way I acquired this was I basically went begging I went into Twitter and said hey I want to do a project with the ZX spectrum does anyone have one they could send me or sell me and a fan from Ireland sent me one they’re kind of hard to find on even on eBay there’s only a couple available so I was very lucky that’s someone sent me one so the keys there’s not very many keys and each key has like what five functions that’s in the same so this rubberized chiclet keyboard is definitely something we’re going to want to improve alright let’s take a look alright so this is probably going to be a row and column um let’s see here’s a CPU the z80 this I believe is the multi-purpose video drive chip the video on this was pretty simple you had I think like 8 different colors and there could be bright or dim versions of each for about 16 different colors and then on any character on screen you can only have 2 of those colors one or the other so it was kind of limiting but they could also do some pretty pretty cool graphics as well if you ever look online they have people still make art with this thing had a very bright posterize look to it so this is going to be your RF regulator come in the side here these are probably going well this thing didn’t output sound to the television so probably X it looks like there’s just there one or two here one of these is probably going to be our composite video in now this was from the UK so it’s pal signal not NTSC like we have here in America however I should have some LCDs that are NTSC and PAL compatible most LCDs made last decade actually are this right here is a heatsink there is you know bog-standard 7 805 linear voltage regulator so this takes the 9 volts in knocks it down to 5 so you don’t really need any special European power adapters for this you just hook voltage up to it and it will work because voltage is the same in different countries now 5 volts DC here is 5 volts DC in England so this had two banks of RAM I believe this is one of the banks and this is the second bank so there is a 16 K model of this and a 48 K and this is the 48 K model because it has both banks and another thing they did to save money it was they actually used defective ram chips that only had half of their capacity working these are 64k chicks but half of their addressing doesn’t work so they’re actually only 32k chips so you’ve got your 16 K base plus 32 48 K anything to save a buck and the speaker is all the basically does is pop on or off it’s very rudimentary although people wrote routines over the years to increase the sound greatly and if we’re going to make this into some sort of portable there is a nice expansion bus here on the back which should have pretty much everything on it I’m not sure if anyone’s actually made a SD card or compact flash disc emulation system for this because this

mostly use tapes you would load off a tape however one thing we could possibly do is create a circuit that would simulate the tape so it would send in all of the you know audio files into this this thing was designed to work with any tape player you’ve had if you had like the Commodore Atari there was a Commodore tape player or an Atari tape player that you needed with this thing you just plug in whatever tape player you had right here and the data transmission was very liberal allowing for variations in the tape even if the speed was it correct it could compensate for that which is pretty cool look uh look into that uh I guess you know what we could do is we could find a tape player and try to load a program onto this all right let’s see if we can get this out of the shell I’ve built many different 8-bit computer mods over the years I’ve done an Atari 800 a couple times and a couple Commodore 64’s Apple two gs and I think that’s it so this is me reaching out across the pod one screw held that in all right now do we get this keyboard apart let’s try these tabs here oh I see this metal plate comes off that makes sense even though this thing was made very cheaply still wasn’t glued together like modern electronics what does that say about us as a people we’re definitely gonna have to keep this Sinclair rainbow that’s pretty normal stuff to masterpiece of cheap design I don’t know if I’m going to really use these keys or not they’re kind of iconic but they’re also kind of mushy I think I’d like to take my own stab at it because if we’re going to rebuild this we might as well remake this we’re not we’re not gonna use this so I like this though this is really cool see your round this time you know Commodore 64 or tari would have had a full mechanical keyboard and this this was cheaper I mean they still use this today in keyboard because it works but man this thing was just so efficiently built it was like the people’s computer it was a Volkswagen of computers now it’s time for a tech timeout today’s tech timeout let’s see what we can do with an oscilloscope we recently got a Tektronix mdo 3104 oscilloscope it’s really nice and I’m using it to analyze the luminance signal coming out of the ZX spectrum video chip so here’s what I did I use the oscilloscope to actually capture images to a thumb drive and I’m going to lay them over each other here in Photoshop and then I’m going to draw red over all of the signals see that so this is actually the individual scan lines that were captured by the oscilloscope I take that red text and compress it Hey look at that it is the text that’s not in the display so analyzing this video signal saving the data to a thumb stick and then analyzing it in Photoshop was a great use for an oscilloscope hi I’m Ben Heck and today we’re going to talk about 3d printing this is way over engineered I guess you could recycle it but I would need like a chipper one thing nice about the laser cutter is it makes a great table as well PlayStation 3 Wii Xbox 360 that was easily the greatest generation of games ever this would probably do some damage to your eye or at least you know give you a headache I used to be able to beat contra without dying this actually shoots out three different laser beams and red green blue so you can actually use this in theory to paint a photo basically just a vacuum chamber I might have to burn myself with a soldering iron many you could point this at a chip and see if the top even like seven years ago I wouldn’t be able to do this I’m Ben Heck and these are my bins I don’t know what I’d ever use this for but I have it well I think this is a good place to stop talking I’d like to be able to put custom roms on to this ZX Spectrum now there’s a big community for ZX Spectrum on the web specifically world’s spectrum which is the top site most old computers have you know user groups still so I was able to

find both the original ROM which is basically the operating system it’s a 16 K operating system contains all the characters basic language and I’ve opened it here in a hex editor there’s also a new ROM called gosh wonderful ROM and it has some improvements such as you can type out words instead of having you know key words and it’s the same size it’s also 16 K because that’s all the bigger the ROM is I thought hey what if I combine these I have this 32 ka prom I pulled out of an old hard disk so that’s what I’m going to do now the EEPROM a 32k EEPROM obviously has to 16 K banks in it the Sinclairs a Lincoln look at one of the time so we could actually we could actually select between top bank and bottom banks you could have a switch which actually toggles which custom OS are going to use so here so I’m going to do it I’m going to take the custom ROM the gosh wonderful ROM I’m going to select all I’m going to copy that okay I’m going to go over here this is the standard ROM it’ll be the first one in memory and I’m going to go to the end and I’m going to insert the data from the second Rob you’re in ecstasy 7f f zero that means it’s basically at the top of 32 K and if you go half way through we see here’s where I pasted the data it’s all in red so if we disabled the first Bank by having a 14 b0 you won’t see this the computer will think this is the start of it so we can actually have a selector between banks so I’m going to actually save this as a custom ROM I’ll call it dual ROM all right now we can burn this image to our EEPROM and I’m going to use the atronics USB EEPROM programmer that I got from element 14 okay the chip is programmed and there’s a piece of tape over it so that the sunlight doesn’t accidentally erase it now we’re going to modify the ZX spectrum so we can stick in this larger EEPROM let’s try and use the ZX spectrum so here’s the motherboard I have this little screen here that I got off the internet a while back we use this for a project but I bought several of them because they were cheap and this screen can do pal and NTSC so it should be able to do the spectrum so I’ve got nine volts going into the screen and that’s also what we need for the spectrum so this right here was the composite signal going to the RF box I disconnected it because we don’t need the RF box so I’ve got that going back into the screen I’m going to tie the spectrum ground together all right now let’s plug in the keyboard because we’ll need it to load from tape let’s see what happens ah there it is okay now this in itself is not very interesting I mean I can type things variable not phone okay let’s see um print hello oh it worked well obviously I can program a game on this and clear now so what I’m going to do is I’m going to use a program that simulates the tape drive this used to use um most people use tapes with this not discs and the tape would play an audio file that would be converted into zeros and ones unload the program it’s kind of slow though so I’ve got my laptop here ha and I found this program called win tzx which means it’s a tape ZX format and I can I found a few files online the Batman seems to work it’s the Batman so what I’ll actually do is I’ll get my laptop here like this I will plug in the headphone jack of the laptop okay now that’s in stereo and I wired it to this to turn it into mono just to make sure the signal is loud enough I have my computer turned all the way up and now I’m going to plug this into the ear jack now this video signal is not very good but these um scrolling lines here show us that the tape is loading and it should tell us the name of it here once it gets the header file and it’s also repeating it through the speaker on the specky I’m just going to call the specky because that’s easy I believe that’s the cool thing to call it hey wanna come over and play some specky this weekend and eat crisps yes don’t need the laptop since it’s loaded I don’t think this is a multiple load

program see I don’t have a Kempston joystick okay great let me let me in the game here we go Batman looks like you use these two keys to go left up and down and then these go left and right remember the part in the Batman movie where he walked around it went oh crap are those bad guys run away oh no I’m dead run away Batman well the system definitely works that’s maybe I’m just supposed to avoid these guys we know this ZX spectrum works so now I’m going to change things with it the first thing I want to try is putting in a new ROM this has the standard OS at the first 16 K Bank and then something called gosh wonderful OS on the second 16 K bank I don’t know if you remember when I was pushing those buttons had typed out an entire word when I pushed one button the new ROM makes it more logical we type in load Loa D instead of hitting J so I’m going to try to put this onto the board it’s never really into the ZX spectrum because I’m American but I think it’s a really cool system and I’m trying to learn as much as I can rapidly I’m going to mount this socket above the surface so I can break some of these points there’s some shocky diodes in here that go for the chip selects so this is you know I’m not going to try to make this small right now I’m just trying to have options what I’m doing here is converting the socket so instead of taking the original ROM it can take an EEPROM or I’d like to say a prom that I’ve programmed now I’m attaching the new socket they do make sockets with long leaves on them but I didn’t have any of those so hence this hack now I’m going to electrically test this to make sure all these connections are correct that way if it doesn’t work later on we know it’s not a connection I’ve used this compact switching regulator in place of the seven 805 that way we don’t need the big heat sink and here is my socket I believe it’s ready to go so I think we should give it a test I’m glad I pulled that 20 year old hard drive out of the back of my mom’s car that one day this is a 32 K EEPROM and it’s replacing a 16 K ROM so there’s basically two images on this EEPROM right after another so address lines 0 through 13 will give you access to the first 16 K a 14 basically selects which 16 K Bank the first one or the second one so we can’t leave this unconnected it is either needs to go low which means the first bank or high which means the second bank that means we can actually put a switch on it so you can select which bank you want to boot into on startup at least I hope that works I’ve got the switch here it’s got two poles in the center pole I’m going to attach the center pole to the a14 line and then these are going to have one going to ground and one going to 5 volts so basically the switch allows you to set if a 14 is high or low and I’m not trying to do this to be Purdy I’m just trying to do it just to test the concept the first bank has original stock rom the second bank has the gosh wonderful ROM so let’s start it up on ROM zero alright now the difference between those is the original ROM if you push a key it’ll type an entire word like load so we would do that in order to load off the tape okay I’ve also added a reset button I still need to fix the video it’s pretty bad alright so I’m going to put the processor in to reset I’m going to switch this to bank – and it looks the same but the difference is if I hit J we just get the letter J we don’t get you know the word I actually have to type out load so yes we can switch between the original ROM and the new ROM just by using an EEPROM that was twice the size and it’s mostly pin-compatible we just removed the one pin that was different which is the a14 line which makes it 32k not 16 the last thing I’m going to fix today is the video Ram the video Ram went here and clearly I’ve removed it the reason I want to remove it a it takes up a lot of space and B these RAM chips use positive

12 volts and negative 5 volts and positive 5 volts three different voltages I’m actually right into this before with old systems I believe the ColecoVision did the same thing I’m over here there’s some circuitry to step up the 9 volt input to 12 volts and also create a negative 5 volt but it better if it just used 5 volts so I remove the chips and then this is the video chip and it accesses the RAM I found an article online about how to replace the RAM so this is what I did I made this little breadboard here which could possibly replace the entire ZX spectrum I could basically rebuild the computer on this breadboard and maybe I will but for now it’s my RAM test this socket is wired to the RAM chips behind this board and these jumper wires basically allow us to virtually plug in this expansion ram into the video chip so I can still use most of the support and test this part so we have a 32 K SRAM a flip-flop and a not gate and what happens is this actually accesses the memory 14 bits and it does it seven bits at a time for a row address select and column address select so the flip-flop does is it basically latches seven bits of the address and then latches the other seven bits of the address and it allows us to connect a modern SRAM that I bought off Alma 14 to the Sinclair spectrum and this Ram only requires five volts let’s see if it works let there be some I conduct in alright the fact that we can see text on the screen and not a garbled mess means that the new video RAM is working well that’s all we’re going to do with this project for this episode but in a future episode we’re going to come back to this and further enhance it and eventually try to get it into a portable form factor in our next episode though we’re going to be working with Minecraft specifically trying to make real-world cubes to simulate the logic that people build in Minecraft game we’ll see you then oh I forgot to hook up this I guess we won’t see what happens yet but you don’t have to take my word for it okay so boring wiring ensues the Ben Heck show is brought to you by element14 the electronic design community and online store built for engineers and hobbyists alike join now and browse the store at element14.com