+selgus Posted February 22, 2023 Share Posted February 22, 2023 Following up from my ATARI 67 XEP Portable project, I have been designing a new portable.. this time for the 7800. It will be a bit smaller than my XEP, but similar design-- LiPo powered, USB-C charging, 5" LCD display, built-in controller and using all original ATARI 7800 ICs (common logics being done in SMD versions). I have most of the system schematic completed, just looking into the reset/power-on circuitry of the original system and some odds and ends.. 15 Quote Link to comment Share on other sites More sharing options...
+karri Posted February 22, 2023 Share Posted February 22, 2023 Do you need to have a donor machine to get the chips or is it possible to buy the chips from somewhere? Quote Link to comment Share on other sites More sharing options...
+-^CrossBow^- Posted February 22, 2023 Share Posted February 22, 2023 9 minutes ago, karri said: Do you need to have a donor machine to get the chips or is it possible to buy the chips from somewhere? It is possible to buy the needed ICs from Best still, but not sure if it would be cheaper to buy a loose 7800 compared to the cost of the ICs. And on at least one of the ICs, the TIA, Best only allows a single purchase per person. 1 Quote Link to comment Share on other sites More sharing options...
+selgus Posted February 22, 2023 Author Share Posted February 22, 2023 10 minutes ago, karri said: Do you need to have a donor machine to get the chips or is it possible to buy the chips from somewhere? BEST has some of the ICs, but I am going to be using donor motherboards. 1 Quote Link to comment Share on other sites More sharing options...
+GoldenWheels Posted February 22, 2023 Share Posted February 22, 2023 19 minutes ago, selgus said: BEST has some of the ICs, but I am going to be using donor motherboards. I will send you a donor motherboard, along with my donor money, and a donor kidney (mine, somebody elses, we'll see how it goes). 8 Quote Link to comment Share on other sites More sharing options...
+karri Posted February 22, 2023 Share Posted February 22, 2023 That may then be pretty expensive. It is the same thing with the Lynx. Replacement Suzy and Mikey chips are really hard to find. The Suzy chips tend to break down due to age. Good luck with the design! 1 Quote Link to comment Share on other sites More sharing options...
SoundGammon Posted February 22, 2023 Share Posted February 22, 2023 It would be cool to have you use the Asteroids BIOS in this! That way you always have a game to play! 1 1 Quote Link to comment Share on other sites More sharing options...
+selgus Posted February 22, 2023 Author Share Posted February 22, 2023 43 minutes ago, GoldenWheels said: I will send you a donor motherboard, along with my donor money, and a donor kidney (mine, somebody elses, we'll see how it goes). Haha! That won't be necessary, as I have motherboards to use for my first prototype and for testing some mods. The main R&D I wish to do now is a better power-on/reset system. The original circuit doesn't lend itself well to a portable. 1 1 Quote Link to comment Share on other sites More sharing options...
+selgus Posted February 24, 2023 Author Share Posted February 24, 2023 Getting closer.. looking into some of the inductors. Also, kept the flip-flop power-on/reset circuitry from the 7800, but also added a main power switch to cut off current from the LiPo to the system (as part of the 7800 circuitry is always active, and the power switch latches to provide voltage to the regulator). I'm not sure if I will keep the original 7800 design here, or just implement my reset circuit. 6 Quote Link to comment Share on other sites More sharing options...
Cris1997XX Posted February 24, 2023 Share Posted February 24, 2023 7 minutes ago, selgus said: Getting closer.. looking into some of the inductors. Also, kept the flip-flop power-on/reset circuitry from the 7800, but also added a main power switch to cut off current from the LiPo to the system (as part of the 7800 circuitry is always active, and the power switch latches to provide voltage to the regulator). I'm not sure if I will keep the original 7800 design here, or just implement my reset circuit. Let's hope this handheld will not become vaporwave! I'll give you Jack Tramiel's soul if that's necessary 😁 2 Quote Link to comment Share on other sites More sharing options...
Shawn Posted February 26, 2023 Share Posted February 26, 2023 On 2/24/2023 at 4:04 PM, Cris1997XX said: Let's hope this handheld will not become vaporwave! I'll give you Jack Tramiel's soul if that's necessary 😁 Vaporwave? Oh ya, tell us another one why don't you? Quote Link to comment Share on other sites More sharing options...
+karri Posted February 26, 2023 Share Posted February 26, 2023 There is always a risk of making mistakes when designing a new pcb. But using the same chips as in the original means that you do not have to make too many inventions. The only thing I wonder about is the choice of a 5" display. A bigger display would appeal more to me. 1 Quote Link to comment Share on other sites More sharing options...
+selgus Posted February 26, 2023 Author Share Posted February 26, 2023 6 hours ago, karri said: There is always a risk of making mistakes when designing a new pcb. But using the same chips as in the original means that you do not have to make too many inventions. The only thing I wonder about is the choice of a 5" display. A bigger display would appeal more to me. For me, the original chipset means that this will be a "real" 7800. Not some emulation of a 7800 (in the places that matter). The 5" LCD fits well with the form factor. This is a hand-held device and I've been using automotive backup camera displays for my ATARI 67XEP portable, so that is carrying over to this project. Schematic is all complete now, and have started routing all the connections (around 40% routed so far).. 7 Quote Link to comment Share on other sites More sharing options...
+mksmith Posted February 28, 2023 Share Posted February 28, 2023 Nice! Best of luck!! Quote Link to comment Share on other sites More sharing options...
+selgus Posted March 2, 2023 Author Share Posted March 2, 2023 Finished routing the board and adding the two ROM signal lines I missed when creating my schematic. My portable will use an EPROM or flash, instead of the standard ROM (in case I wish to make some sort of boot-up modifications). I'm going to make a few PCBs now for testing.. 8 1 Quote Link to comment Share on other sites More sharing options...
+selgus Posted March 3, 2023 Author Share Posted March 3, 2023 Now with the main PCB designed and being manufactured now, I started creating the small controller fire buttons board. Pretty simple, going for the CX-78 controller design, built into the enclosure. Also started the 3d model prototyping the enclosure and here for size comparison for my portable (called an ATARI 7800 portSYSTEM) to the standard proSYSTEM enclosure.. 4 Quote Link to comment Share on other sites More sharing options...
+karri Posted March 5, 2023 Share Posted March 5, 2023 Looking at your pcb there seems to be some components with awfully small footprints. Do you plan to solder these by yourself? Also, are you aiming for a NTSC unit? Quote Link to comment Share on other sites More sharing options...
+selgus Posted March 5, 2023 Author Share Posted March 5, 2023 37 minutes ago, karri said: Looking at your pcb there seems to be some components with awfully small footprints. Do you plan to solder these by yourself? Also, are you aiming for a NTSC unit? Yeah, I've been doing this type of design for some time now and for all my prototyping/small runs, I solder by hand with a quality soldering station and hot air. Good magnification really helps! When I've transitioned to mass production, I usually have a service do it with pick-and-place machinery. You are correct, this is an NTSC version, I haven't looked at the differences between PAL (though I don't have any of the RF circuitry, so that simplifies it a bit). I did need to make a second revision of my board already, as I replaced the flip-flip power-on button nonsense from the stock 7800 with a MCP130 IC. All I needed the reset circuit, as I have a power toggle for the whole unit. The 7800 actually always has a section of the device always hot, so the flip-flop can power-up the machine. 2 Quote Link to comment Share on other sites More sharing options...
+karri Posted March 5, 2023 Share Posted March 5, 2023 Hand soldering stuff like that exceeds my talents. A small NTSC unit that can read real carts would be pretty ideal as you could have it in your hand luggage. The other option is using an emulator. But the real thing is always nicer. My guess is that the PAL unit might run on a different xtal (4.433619MHz). There is probably also some changes in the circuitry for 50 Hz frame rate. 1 Quote Link to comment Share on other sites More sharing options...
+selgus Posted March 5, 2023 Author Share Posted March 5, 2023 14 minutes ago, karri said: Hand soldering stuff like that exceeds my talents. A small NTSC unit that can read real carts would be pretty ideal as you could have it in your hand luggage. The other option is using an emulator. But the real thing is always nicer. My guess is that the PAL unit might run on a different xtal (4.433619MHz). There is probably also some changes in the circuitry for 50 Hz frame rate. Yeah, that was the reason I started this project-- to have a 'real' 7800 that could play standard cartridge games, but in a small portable form-factor. I just started looking at the PAL schematic, and it looks like that crystal is in addition to the NTSC circuitry. Plus looks like it uses a different TIA chip, with different pinouts. Would be nice if someone has done a 'diff' on the NTSC and PAL 7800 schematics.. I might make a version of the schematics/board design for PAL, if there was much interest. 2 Quote Link to comment Share on other sites More sharing options...
+selgus Posted March 8, 2023 Author Share Posted March 8, 2023 So I did take a closer look at a NTSC vs. PAL machine (at least from the schematics, as I don't own a PAL motherboard), and there are quite a few differences. The obvious is the different TIA's that have different pinouts, and then there is how MARIA uses the clock lines. I tried to extract each change and create a schematic and board design, that would allow the device to be either NTSC or PAL. This is the result of my work.. The board has 6 jumpers, that take care of the differences between the NTSC and PAL custom chips, vectoring the proper signals to the appropriate pins, and one to enable +5V to enable power to the PAL circuitry. If all the jumpers are set to the right, it is NTSC, to the left PAL. To make a NTSC device, I just won't populate the PAL section under the TIA, along with not populating the 4.4336HMz crystal. There is also a few components removed from the R/W signal on 7800 PAL motherboards, but I left this alone for now. I will need to do some testing first. This will need to be validated by actually making a board and populating one as NTSC and another as PAL (and also getting my hands on PAL versions of some the custom chips). At least I feel, in theory, I can make a single motherboard to cover both. Oh, and I fixed in issue with my base design, where I had some of the buttons in the wrong physical locations on the board.. so rerouted them. 2 Quote Link to comment Share on other sites More sharing options...
+karri Posted March 8, 2023 Share Posted March 8, 2023 1 hour ago, selgus said: At least I feel, in theory, I can make a single motherboard to cover both. It is not so important to cover both machines. But as for understanding the differences it would be nice to document them. I am really curious to see how this project turns out in the end. 1 Quote Link to comment Share on other sites More sharing options...
+selgus Posted March 13, 2023 Author Share Posted March 13, 2023 Received my first test PCBs, which I knew were not final (as I had some of the buttons in the wrong locations, had the old flip-flop power on/reset circuitry of the original 7800 and a few other minor changes). Size-wise, it is about the same size as my SEGA Genesis portable, and smaller than my ATARI 67xep portable. For the 7800 portable, I am going to make the enclosure mimic the original case design, but with an LCD panel on front and cartridge inserted from on top. I installed the 7800 cartridge socket and then tried testing a standard 7800 cartridge and found an issue-- the 7800 cartridge PCBs are deeper than the ATARI 8-bit line, inside the enclosure, so it could not be inserted into the socket. Ugh. So back to my design and I needed to reshape the board outline and rip up a bunch of traces and do a bit or re-layout.. to get this, hopefully the last revision of the board.. 8 2 Quote Link to comment Share on other sites More sharing options...
+karri Posted March 13, 2023 Share Posted March 13, 2023 57 minutes ago, selgus said: 7800 cartridge PCBs are deeper Bummer! That is a pretty big operation to re-route in such a tight area. Quote Link to comment Share on other sites More sharing options...
+selgus Posted April 11, 2023 Author Share Posted April 11, 2023 Been trying to finalize the board layout for the form-factor I want for the portable.. so been working on the enclosure. Here is the current state.. 17 Quote Link to comment Share on other sites More sharing options...
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