N00b help! need a something to perform this function

Discussion in 'The Projects Forum' started by frozenlead, Mar 30, 2008.

  1. frozenlead

    Thread Starter Member

    Mar 30, 2008
    19
    0
    I'm making an Apollo Command Module simulator using a number of computers and custom made and modded equipment, but i'm stuck on how to perform one critical action.
    Instead of engineering my own drivers and such, I decided to route the switches of the simulator into a modified keyboard, which will then allow input into a computer and into a mission control environment. However, due to the keyboard memory limit, i can only press so many keys at a time before the keyboard can't see any more being pressed.
    So, each switch in the simulator will be as the originals on the real capsule - single pole, double throw. I need a way for when the switch is thrown in either direction for it to provide a burst of current to connect the keyboard circuit and send a keypress command to the SIMcomputer. The only way I could think is to connect a motor to each switch position, and have that rotate a metal dongle, which would connect the two contacts on the inside of the keyboard - but that quickly gets expensive, and large, and the motor would be continously running, giving multiple keypress commands - i simply want one. I could hook up a transistor setup to that to shut it off, but i still would like to get rid of the motor completely. Is there some kind of component someone knows of that can perform this function? (prefer it to be cheap, possibly home-manufacturable, and if at all possible, simple and small.)
    thanks!
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Interesting project! Post some pictures!

    Take a look at this page:
    http://www.mikesflightdeck.com/keyboard_port_1.htm
    Rather than trying to build something to push a key on a keyboard, I would opt to build a keyboard emulator using a PIC. You could have the PIC scan your SPDT switch array, and send a keyboard scan signal to your computer's keyboard port when a change of state has been detected. You'll save a lot of wiring this way.
     
  3. frozenlead

    Thread Starter Member

    Mar 30, 2008
    19
    0
    Awe, and I thought the keyboard interface idea was original...oh well. I'll be happy knowing I thought it up myself. I'll read up and get back to you.
    And I'm making a web site about the project - coming soon!
     
  4. frozenlead

    Thread Starter Member

    Mar 30, 2008
    19
    0
    Could I use a relay to do the switching? I'm not sure what one does exactly, I've never used one before.
    From what I gather, when it receives a signal from one circuit, it actuates a solenoid that closes or opens another circuit.
    Is there a relay that will close/open a circuit for just a split second, and then perform the opposite operation?
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I'm not sure exactly what you're talking about switching!

    If you mean keyboard scan codes; I wouldn't recommend that. Relay contacts "slide" when breaking and "bounce" when making contact, besides being relatively slow (actually, agonizingly slow in comparison with solid state devices.)

    Not sure what a relay does? Well, a relay has one or more sets of contacts inside that are moved magnetically when a coil is energized. They are usually spring-loaded so that they return to a set position when de-energized.

    I'm not certain as to what approach you are talking about.
    I suggest that relays are to be avoided whenever possible. They are large, slow, noisy, expensive, and use a LOT of power compared to semiconductor devices - along with having a far more limited life span.

    You might consider getting Myke Predko's book that was recommended on the first link I posted. I ordered a copy myself. What I paid for the book & shipping was less than three Radio Shack relays ;)
    Myke's site:
    http://www.myke.com/pic-book.htm
     
  6. frozenlead

    Thread Starter Member

    Mar 30, 2008
    19
    0
    The design requires that a user throw a switch, which closes the first circuit (the one I don't know how to build). That first circuit, while staying closed, must close then open another circuit quickly. That switch it presses will be the two contacts below a keyboard key. Then the keypress will be picked up by the software i wrote already, and the computer will perform an appropriate function on the simulator.
    The relay and solenoid thing was last ditch - I very agree, I'd much rather use semiconductors than mechanical parts.
    I was already going to get the book, couldn't resist!

    If I can figure out this circuit though, without having to buy IC's or something, I'd be real happy.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, I have some good news for you. If you buy Myke Predko's book, it comes with a PCB that you can populate with inexpensive components to build an inexpensive PIC programmer, that handles several families of PICs. The variations of the programmer circuit are documented on his website. The components that go into the PCB are widely available, and very inexpensive.

    The better news is that PIC MPU's are dirt cheap; just a couple bucks apiece. You would spend more buying a single relay than buying most PICs.

    I'm not sure that you're quite understanding what the switch-to-PIC-to-keyboard interface is going to do for you yet. The PIC will be able to detect a change in your command switch positions by scanning your switch grid. The PIC can then send a combination of keystroke scan codes right to the computer's keyboard port, without the need for a physical keyboard being present.

    How many switches are you going to have in your setup?

    It's been a couple of years since I had a look in an Apollo command module. Kennedy Space Center is about 45 minutes from me. They have a couple of command modules sitting there with plexiglas over the hatch; you can see in but it's rather dim, and due to the plexiglas, flash photos don't work very well. The Saturn V they've restored is quite impressive, though.

    I hope you've found an inexpensive source for reliable switches, as that will likely be your "big ticket" item now.
     
  8. frozenlead

    Thread Starter Member

    Mar 30, 2008
    19
    0
    I don't remember the exact number of switches off hand. it's a few hundred. i understood what the interface does, I would just rather skip putting the IC into it and such - it's something i'm fairly inexperienced with. modding the keyboard was my best, cheapest, and readily available option.
    I'm getting the book though. Gotta learn new things to move forward.

    And I have the switches already. many more than I need.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, you're going to need to connect all of those switches to something.

    Believe me, it's going to be a heck of a lot easier to do this with microcontrollers like a PIC than trying to interface all of those switches with relays or the like. Yes, it's going to be a learning experience - but this is quite a large and complex project.

    The original command module panels included 24 instruments, 566 switches, 40 event indicators, and 71 lights, according to Wikipedia. That's a LOT of wiring! :eek:
    http://en.wikipedia.org/wiki/Command_Module
    Your best bet would be to make PCB's for the switches & lights, rather than trying to wire all of that stuff by hand. That way, you can use dual-row pin headers and ribbon cables to plug everything together; cheap, easy to get and reliable.

    What do your switches look like? Do you have a manufacturer & part number for them, link to a datasheet, or an image?
     
  10. frozenlead

    Thread Starter Member

    Mar 30, 2008
    19
    0
    I wouldn't dare wire that by hand, the PCB had been in my plan...though it'd expected to make a few molex connections to a keyboard. The better idea does seem to be the PIC.
    My Sim doesn't include all 556 switches. I eliminated a FEW of them that really didn't seem needed, or just didn't fit the space constraints. (over the shoulder ones, a few of the fuses, etc.)
    The switches are silver toggles, with round bases. Not exactly like the originals, but hey, they were free from a buddy. Dunno on the model or anything. I figure they'll be okay. They won't be pulling much at all.

    Got a suggestion as to how the light the switch panels? they've all got a lot of writing on them to designate the switches. The way I designed it, there will be a gap in each panel by the switch rows to install a clear computer-printed sheet. Then I figured i'd line the back with plastic and put LED's up to the task (in the original blue, of course).

    I am working off of the official control panel plans from nasa. Amazing what they'll give you if you ask nice.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, I'm getting the same book. No PICs here yet; I've had a couple of Basic Stamps (BS2e, BS2sx) kicking around for a number of years. They're quite a bit more expensive than the PICs, hence less popular. Time to experiment with something different. ;)
    I don't blame you. That'll keep your checklist slightly less user-hostile. ;)

    Pulling much current, you mean? No, not much at all - less than a milliamp.

    The military aircraft instrumentation panels I've dealt with have been what seems like engraved Plexiglas, perhaps 3/16" or 1/4" thick. Small incandescent lamps are placed at strategic intervals around the panel to provide lighting. The majority of the face of the panel is either flat black, or battleship gray, depending upon where it is in the cockpit. The engraved characters on the painted surface appear as very uniformly illuminated. Military aircraft use red for lighting, to avoid night blindness. That didn't matter in the Apollo missions; energy conservation did.

    It might be pretty expensive to get a bunch of painted Plexiglas custom-engraved/routed for this project - but it would be really cool when completed. You could install blue LED's by drilling holes around the edges of the panels (drilling parallel to the face, that is).

    Plastic sheet stock with a translucent coat or perhaps translucent itself might work pretty well, if you can use a laserprinter or inkjet to print in black on the reverse side (reversing the character images of course) to act as a mask. I'm not sure what's available in that kind of thing.

    Sweet! :D

    Scan 'n' post 'em!!
     
  12. frozenlead

    Thread Starter Member

    Mar 30, 2008
    19
    0
    The panel diagrams will be up on the website when i make it.

    However, that's pure genius on the Plexiglases idea. I can get it cheap, I know a few people. I'll make the entire board panel from plexiglass, support it in places with wood and pain the entire thing with lines and lettering masks on. When it all comes off, those letters will come out clear.

    Idunno why I didn't think of that. These panels are very massive, though, wait till you see the site.
     
  13. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Actually, I'm afraid that using masks won't work very well.

    The engraving serves to disturb the optical characteristics of the clear Plexiglas, and as the egress point for the light. Otherwise, the light just bounces around inside the sheet of Plexiglas. If you simply use masks, the surface of the Plexiglas will be undisturbed, and light shined in from the edges won't show.

    It would be a good idea to make a lot of smaller panels, rather than few large panels. It will be much easier to access things when you need to make repairs, replace switches, etc. - besides, if you happen to "botch" a small panel, that's no big deal.

    There are places that do engraving for things like signs, trophies, nameplates for desks, etc. - you could get some prices from them.

    It may turn out to be cheaper to build your own CNC mill ;) That could be a very fun project all in itself - and you could possibly make money with it.
     
  14. frozenlead

    Thread Starter Member

    Mar 30, 2008
    19
    0
    I was saying the panel in itself was huge - NASA had the idea that smaller panels making one big one was a good idea too; I intended to follow it. It's actually split into 10 or so smaller panels. But the main panel, as a whole, is tremendous. This also doesn't include the side panels. Some of them, as I mentioned, I won't be needing, as the side panels are mainly fuses, but some of them are more important things like re-pressurizing valves.
    Even if the plexiglass isn't engraved, the blue will still show through to highlight the lettering. (I do understand physics though!) It depends on where I position the lamps. I may just line it with a cathode-cord type light, instead of LED's.
    Not far along enough to say, yet.
     
Loading...