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Derek Andrews

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Posts posted by Derek Andrews

  2. Posted

    Thanks, that is interesting but I honestly don't know if they ever actually sold any of those. But yes, I did all the design work for DAZRAM. Given that it was nearly forty years ago, I don't think I can add much beyond what is in the advert. One end plugged into the ZX81, presumably an expansion port, and it had a ROM with Z80 code that I wrote to allow the user to input 2650 machine code. The code was stored in a RAM and connected to the Database cartridge. Given that the user was going to have to write their program in assembler and convert it to machine code themselves, and the complexity of programming the console to do very much at all, it would have taken someone with a lot of perseverance to get very far. This was probably one of the crazier things I have ever been involved in, but I was getting paid to do it.

    • Like 2

  3. Posted

    I admit that I'm inexperienced with electronics, but wouldn't NE and SW produce the same result electrically? They both connect the same wires (1,2,6,10).

     

    The joystick circuitry is odd indeed, and I can't say that I fully understand it.

     

    The 2637 pins 8 to 11 that read the joystick switches are analog inputs that are measured by an analog to digital converter on the chip. The asymmetric values of the resistors and capacitors in the circuit (10k/470k ohm and 0.1/0.047 (uF?) ) must be significant, perhaps forming some sort of timing circuit, but that is just a guess. I have no idea what the jack plugs J1 and J2 are connected to or what role they play.

  4. Posted

    Looking at the schematic, I see that the keypad rows go to a different chip than the columns. Each one has a single wire, do they alternate acting as ground?

     

    Yes. The 74LS145 is used to output a logic 0 to one of the six sets of four keys each. The 74LS258 is used to decide which of the two handsets to read, and outputs the state of the four keys selected by the '145 to the low bits of the databus.

     

    http://www.ti.com/lit/ds/symlink/sn74ls145.pdf

    http://www.ti.com/lit/ds/symlink/sn74ls258b.pdf

    https://console5.com/techwiki/images/f/f0/Emerson-Arcadia-Schematic.png

  7. Posted · Edited by Derek Andrews

    Hmmm is appears the higher the number on speed the slower the chip...

     

    A bit late replying on this, but yes, and for the record:

     

    The 'speed' of these memory chips is usually quoted as an access time. A -150 signifies a memory device whose contents can be accessed in 150ns. A -200 takes 200ns for the data output to be valid.

     

    Conversely, microprocessors are specified to work at a particular clock rate, for example the Z80 ran with a clock rate of 2.5 MHz, the Z80A runs at 4MHz, the Z80B at 6MHz.

  8. Posted

    I finally broke down and bought myself not one, but two Voltmace Databases. It will be a while before I have the time to get them powered up on 110v and displaying their video, but in the meantime I plan to open them up and document their construction. I have a list of things I want to record (below), but wonder what others might like to see recorded for posterity.

     

    Photos of the original box artwork.

    Photos of the polystyrene packaging.

    Photos of the mouldings with dimensions.

    Photos of the circuit board, top, bottom and one superimposed on the other, from which a circuit diagram could be constructed.

    Parts list.

    Manufacturer and date code of all the IC's which may give a clue as to the approximate vintage of these two consoles.

    Ditto the cartridge wiring and construction. (My regional library has a 3D scanner and printers, so I will see if it is possible to scan the two parts of the cartridge mouldings and print new ones).

     

    • Like 4

  9. Posted

    Now are you asking out of curiosity, or to gauge interest in new products (software or hardware) before you invest time and money into those projects? I seem to remember you used to be one of the original developers, looking to get back into the system so it would make perfect sense to determine if it is worth your time to develop new games, if anyone is willing to play / buy those in the end.

     

    Sorry, I guess I missed your post when you made it Carlsson.

     

    A bit of both really. I am working on a game, as time and enthusiasm permits, and have some other ideas too. I don't mind investing my time in the project as a hobby, but money is tight for me these days, and so far everything I have done has been with the WinArcadia emulator. I have no dreams of making money from the effort, but would like to cover some of the costs of buying a console and other hardware for test purposes, so wonder what sort of interest there would be in a new game, whether I could justify making cartridges, or just making binaries available for download and seeking support via Patreon. I might also make the source code and documentation available, either as a download or print on demand book.

     

    I am also interested in exploring just what the console could have done if the the cost of rom and ram were less prohibitive back in the early 80's.

    • Like 3

  10. Posted

    What I am looking for is something to plug into an Interton VC4000 type console that will emulate the ROM and RAM in a game cartridge. It would need to connect to a PC via cable, Bluetooth or Wi-Fi and would be used for the purpose of game development.

     

    Does such a thing already exist? It seems to me that something like this would be quite possible using something like an Arduino or Raspberry Pi, but don't want to re-invent the wheel if there is already something out there that will do the job.

  11. Posted

    RCA on the console? It's analog RF and needs a converter to convert the signal -- the old machine had a twin-lead thing but you could find one that transformed to coax.

     

    What's between your Atari and your Tv? Got a picture?

    Yes, its a rca/phono type socket on the console, and yes it is analog rf.

     

    RCA-Ftype adapter, then coax cable to tv.

    Yes, I have a picture, just not very good and some games the colour contrast is minimal.

     

     

  12. Posted

    Not normal. Doubt it's a impedance mismatch.

    Try a different feed line (coax cable).

    What happens if you connect the Atari to the VCR, then the VCR to the TV?

    I'm using a RCA to F type adapter at the console connected via coax cable to the tv.

     

    I will try going through the VCR, but need to get another coax cable first.

  13. Posted

    Not that I can see. I'll go through the menus again just in case I missed something, but there are no physical controls. Picture quality on VCR is fine though, so I don't think this is the problem.

    Found it, but doesn't really help any.

  14. Posted

    Isn't there a brightness control on the TV? or contrast?

    Not that I can see. I'll go through the menus again just in case I missed something, but there are no physical controls. Picture quality on VCR is fine though, so I don't think this is the problem.

  15. Posted

    I recently broke down and bought my first ever console, an Atari Junior, along with a variety of cartridges, and have just got it hooked up to an NTSC crt tv. I'm none too happy with the picture quality in terms of colour contrast. Some games are playable, but Frogger has some things that are difficult to see, and Popeye is next to impossible to play as the platforms and ladders are only barely visible. I'm just wondering if this is normal for NTSC? I recall the tv engineer at Voltmace telling me that NTSC stood for Never Twice Same Color ;-) Or is there a problem:

     

    1. Faulty console

    2. Connection problem (impedance mismatch, connecting the RCA on the console to the BNC on the tv)

     

    The tv works fine with VCR. There doesn't appear to be anyway to adjust colour on it.

  16. Posted

    Good video. I like the HKC monitor and will have to try and find one, or something similar. I really would like to get a system set up here (in Canada) so that I can do more game development. The WinArcadia emulator that I am using is terrific up to a point, but somethings like joystick control really need checking out with real hardware (though of course even the joysticks vary between manufacturers) and the fact that some games don't run on it indicate that the emulation is not perfect.

    • Like 1

  23. Posted

    If you post some examples, we can probably tell you if they seem reasonable or not.

     

    OK, here is one. I offered $60CDN and never got a response. Not sure if that means it was already sold or the seller expected more:

     

    "Atari 2600 in box with several controllers/game pads, trak-ball attachment and roughly 60 games. System isnt getting power I believe the power jack solder broke off inside. Just needs to be taken apart and resoldered. Open to offers"

  24. Posted

    I have been keeping an eye open for 2nd generation consoles and I keep coming across adverts for machines that are either untested, 'just needs such and such fixing', or parts missing, such as power pack (and hence probably untested). Other than their possible value for spare components, or sometimes the carts that come with them, are they really worth gambling more than say $20 on? Some people are asking $100+, plus shipping. I'm new to this and until recently didn't realise there was so much interest in old games, so any comments on the state of the market would be appreciated.

  25. Posted

    I learnt some FORTRAN while I was still at school. We wrote the program on coding forms which were sent off to Bristol University where someone punched cards, the program was run, and if it didn't exceed our allocated processing time etc, we got a print-out back in a week or so time ;-)

    I also vaguely remember us having some sort of weird programmable calculator that involved a paper tape punch.

     

    Things weren't much better a few years later after I graduated and got a job at TI(UK) programming ATE for memory chips. More punched cards and reams of paper! Eventually allowed time on a TI990 for writing programs, then had to lug reels of tape around, which were just as heavy as the cards.

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