Questions about my DIY Launch Controller

Discussion in 'Ground Support' started by BrainlordMesomorph, Apr 8, 2018.

  1. May 1, 2018 #41

    BrainlordMesomorph

    BrainlordMesomorph

    BrainlordMesomorph

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    Steve, a couple of more Qs:

    The Continuity test is going to light up the "Commit" LED (but dimly? b/c of the 350 ohm resistor?) but that really the LED should only come on w/ the ignition button. Is there any way to do that?

    And on the topic, it seems to me that there should be several things that can only happen *after* a *successful* continuity test, (i.e the arming key switch, and the ignition button) can we do that?

    We would need to flip a switch with a momentary zap of electricity - is that a relay? (or does a relay only work while it has power?)
     
  2. May 1, 2018 #42

    Steve Shannon

    Steve Shannon

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    I’m not sure what the purpose of the commit led is. It will light up when either the continuity switch is closed or the ignition switch is closed (brighter). When you close the continuity switch the current flows through the cont. switch, through the continuity led and through igniter and the commit led (assuming the voltage drop across the igniter is greater than the forward voltage of the commit led; it probably won’t be with this low of current) before returning to ground. When the ignition switch is pressed you will have a voltage divider between the commit led and the igniter. I’d get rid of the commit led, but I like simple.
    Adding some kind of sequential logic (i.e. things that can only happen after a successful continuity test) is just another way of making your circuit more complex and doesn’t really do anything for safety or reliability. We frequently see continuity but due to poor conductivity don’t get ignition when the launch switch is pressed. Usually that’s caused by poor contact at the igniter clips and cleaning the clips and taking a couple wraps of the igniter leads around the clips cures it. Some folks have used diodes as igniters. They would not pass the continuity test, but you would want the ability to press the launch switch nevertheless.
    Getting a relay to permanently latch after temporarily powering the coil is most easily done by feeding power back from the controlled contact to the coil. Otherwise you can just purchase a latching relay. To open either all power must be removed from the relay.
     
  3. May 1, 2018 #43

    BrainlordMesomorph

    BrainlordMesomorph

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    I'm a software engineer (or can't you tell) I'm all about sequential logic
    (and if I wanted this to be simple.....) :)


    Oooh, ooh, you mean I would need a "bypass" switch, too? :D

    And *diodes?* why? are they reusable or something?


    Would that be this thing? https://www.ebay.com/itm/3V-24V-5A-...A-LED-Relay-/182205169672?hash=item2a6c464008

    EDIT: and now that I read the words "flip flop" I remember my 65-in-1 set!
     
  4. May 1, 2018 #44

    Steve Shannon

    Steve Shannon

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    I don’t remember exactly who it was, but someone drove diodes to failure and they got really hot and worked well as igniters. It was years ago. I don’t remember whether they reverse biased them or not.

    Yeah, you can add a bypass switch, but that’s a patch on top of faulty code. Wouldn’t you rather keep your code simple? My first job was as a software engineer, but we didn’t have the memory for code or data that people have now. That forces you to think differently, I guess.

    Finally, that’s no relay.
    IMG_0209.JPG
    That’s a relay.
     
  5. May 1, 2018 #45

    BrainlordMesomorph

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    a 40 amp relay that consumes 2 watts? (and cost $12)

    OK, OK I am going too far.

    :)
    EDIT LOL to the Crocodile DunDee reference.
     
  6. May 13, 2018 #46

    DanielLW

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    I don't know how far along you are with your build, but if you want to solve the problem with your status light dimly illuminating during continuity checks, consider using this modified circuit:

    Continuity 2.jpg

    The main difference in this circuit is that it places the launch button on the "negative" side of the igniter, and uses an NPN transistor as a switch to illuminate the LED. The advantage of this is that it uses very little current to test the igniter - just 1.11 milliamps. This is a little safer since it puts less current through the igniter. It probably doesn't matter as much today, but launch controllers used to require being "flashbulb safe" back when people would sometimes use flashbulbs to light rockets. (old fashioned flashbulbs will light with very little current)

    One other thing I notice is you "commit" LED. If your connection is good, your commit light will not light when you press the launch button in your current configuration. The reason for this is because that LED will be shorted by the igniter, and as a result it may not light at all until after the igniter has burned. For that matter, all your LEDs may dim or extinguish once the launch button is depressed. Something to consider.

    Also, on the schematic, ignore the 1 ohm resistor and ground. Those are just there because the simulation software I used requires a ground, and gave me an error when I "shorted" the power supply.

    Let us know how it turns out. Pics or it didn't happen!
     
  7. May 14, 2018 #47

    BrainlordMesomorph

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    Hi Daniel,

    Thanks, I think I see what you did there.
    But I think you forgot to add the commit LED. :) (I assume it goes in the right bottom corner between the transistor and the launch button?)

    And what do the green arrows and speeding purple dots mean?

    And as for where I am:
    Almost all the parts have arrived, (not the flashing circuit kit yet) and I'm thinking my "first draft" of this thing will just focus on functionality. (1st launching rockets, then flashing lights.) And I'm learning that just attaching things to the inside of this Pelican Case is going to be challenge.

    Epoxy and CA won't work on it. Drilling into will violate its water tightness. The manufacturer recommends a certain 3M glue that's $40 a tube and needs a $6 dispenser gun (which needs a $3 single use nozzle - there is discussion about not needing the nozzle)

    There is a $4 glue from locktite that *claims* to do it, undoubtedly not as well as the $40 glue.

    Superduper velcro may work for the batteries.
     
  8. May 15, 2018 #48

    DanielLW

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    The green arrows just indicate signal flow. The purple dots are put in there by the simulation program. When animated, they are kinda like an oscilloscope output. The program is EveryCircuit.

    I didn't forget the commit LED per se. I played around with it a bit but the only way I can think of to get it to work is to use a double pole double throw button to complete both a commit light circuit and the ignition circuit simultaneously.

    But even with the button on the positive side and your existing continuity check, there are two issues with the commit light:

    First, pressing the launch button completes the ignition circuit, which is a very low resistance circuit. The battery will deliver a lot of current to that pathway, and may not have enough current delivery capability to run loads with high resistance. So the commit light may not light at all until after the igniter burns through, thus opening the ignition path.

    The other issue is once you press the launch button, do you really want to be looking at your launch controller rather than the rocket?
     
  9. Jun 19, 2018 #49

    BrainlordMesomorph

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    OK the parts are here. I'm getting to this.

    Things are very different sizes than I thought, so here's the (current) WIP control board:


    [​IMG]



    I made some changes to the schematic, I eliminated some complexity... and then created more complexity :D

    [​IMG]

    The red line is the prototype, that's what i need to launch rockets, I'll build that first, once it works then I'll add the other stuff.

    Main changes are:
    1. Got rid of the Commit light and the entire "status board" , mainly for space, but a couple of its LEDs did hang around near the key switch.
    2. 4th position in Pad Select switch is now "All Pads"
    3. (I think) I added a flashing LED at the Pads. (yes I know the will they will all flash at once, but only if they are plugged in)

    4. And I'm TRYING to set up the peizo to make three different noises at three different times:
    (i've routed it through the NC side of the ignition button)
    In its current position, during a Continuity Test, it should be on the low voltage side of the circuit and make a low steady tone: "Booooooooooop"
    after the Keyswitch is thrown, the flasher unit kicks in and it gets higher a intermittent current " Teeet..... teeet.... teeet."
    Then, when the ignition button is pressed, that cuts out the flasher unit, and the peizo is now on the high voltage circuit, "BEEEEEEEEEEEEEP"

    I *think* that would all actually work, but in the process; I've totally shorted out the Continuity Test, and I looks like the flasher unit could accidentally LAUNCH THE ROCKET!

    but... its close.

    Diodes? Could they be employed to fix that??

    Just moving the existing LEDs??

    I'm so close. I can almost see it.

    But that leaves me with what to do with V- on the LED1 of the flasher unit (blue dotted line and question mark)

    And one last question:
    Gel batteries, no problem laying then on their sides (forever) right? I have to if I'm going to use this box.

    v
     
  10. Jun 19, 2018 #50

    Voyager1

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    Just at a quick comment. There is an issue with point 2 above. I think you will find that positions 1-4 will select “All Pads”, as you have shorted them all together on the output side of the rotary switch.

    The gel battery should be fine on its side. I’ve been using them in my launch gear on their side for years. Others may beg to differ on that, but I have had no issues - yet!

    Also, I don’t know how your flasher unit is wired, but I think you might have issues there, too. Even if it does work that way, you might have too little current to drive the paralleled LEDs on your ignition leads. You better breadboard that circuit.
     
    Last edited: Jun 19, 2018
  11. Jun 19, 2018 #51

    BrainlordMesomorph

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    DUH! of course they will!

    But wait, then how do I wire that up? diodes??
     
  12. Jun 19, 2018 #52

    BrainlordMesomorph

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    OK I think I solved everything!

    [​IMG]
    A 2nd piezo gives a continuity and launch tones and I still have my teet,teet,teet, (and solves what to do w/ V- from the flasher unit.) without shorting out the launch system.

    and I added (squeezed in) diodes to the All Pads select, to avoid that cross circuit.

    ... I think that solves everything.

    Yes I know, we don't actually know if there enough juice to actually power all the beepers and lights and everything. We'll find out.

    1 last question,
    Can somebody please tell me precisely what diodes I need to buy for the All Pads select? (I have no idea)

    BTW: here is the flasher unit: https://www.ebay.com/itm/DIY-Kit-5M...e-flash-Circuit-Production-Suite/400985396241 It came as just a palm sized bag of parts. not even a schematic other than what printed on the board. that's going to be a fun little project in itself.
     
    Last edited: Jun 19, 2018
  13. Jun 19, 2018 #53

    Voyager1

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    Looking at the circuit board of your flasher kit suggests to me that the way you’ve wired the LED1 output of the flasher in series with a piezo through your ignition push button might not work.

    The transistor(s) (9014) on the board are NPN type and are probably connected as a common emitter so that the LEDs are in the collector circuit. If this is the case then it is likely that the LEDs are connected with the cathode to the transistors’ collector, and the anode to the positive supply rail. The parallel connection through to pin2 of the 3-pin connectors might also be an issue since this goes through to the ground via the LEDs in the ignition leads, instead of returning back through the transistor switch.

    I am, of course, making several assumptions here because I have no information on the circuit topology of the flasher module. I do believe that you will need to breadboard parts of your circuit to check whether your design is valid and workable.
     
  14. Jun 20, 2018 #54

    BrainlordMesomorph

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    Someone else in the thread suggested that would be a workaround if the flasher's peizo wasn't getting enough juice.

    Everything from the flasher unit out, is Phase 3, and experimental.

    Phase 1: Mounting everything in the box, and wiring the red circuit. (then I can launch rockets)
    Phase 2: The simple LEDs and Aux Power systems
    Phase 3: Flashing LEDs, and/or Beeping and/or flashing LED at the pad (depending on what works)
    Phase 4: Eggfinder RX unit

    but to repeat:
    1 last question,
    Can somebody please tell me precisely what diodes I need to buy for the All Pads select? (I have no idea)
     
  15. Jun 20, 2018 #55

    BrainlordMesomorph

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  16. Jun 21, 2018 #56

    Voyager1

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    The diodes you require for this will need to be rated for at least 10A, preferably higher, say 15A. One particular example that comes to mind is a 10SQ050 or 15SQ050. These are 10A and 15A, respectively, at 50V.

    If you intend to fire all 3 ignition circuits simultaneously, then you will need to upgrade your 10A fuse before the power switch. A typical e-match or FirstFire igniter is about 1.5 - 2 Ohms. This means your igniter will draw about 6-8A. Three igniters will draw 18-24A. This is only for a second or two, but long enough to trip a 10A circuit breaker. So, think about a minimum of 25A for your breaker. This, of course, reduces your short circuit safety margin for when you are only using one igniter. You might be better off putting a 10A fuse in each ignition output, but still leave the 25A one at the power switch.
     
    Last edited: Jun 21, 2018
  17. Jun 27, 2018 #57

    BrainlordMesomorph

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    Thank you. I'm building for future-compatibility. I have no current plans to launch 3 rockets at once. Should I ever try it, and blow that fuse, I'll remember "Yep That guy told me that would happen." and proceed to upgrade the fuses. :D

    Other question:
    I'm looking at this XLR cable I;m using. It has 3 lines. 1 and 2 are insulated wires, 3 is a copper mesh wrapped around 1 and 2. I'm guessing 3 is V negative?
     
  18. Jun 28, 2018 #58

    Voyager1

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    Yep, the braided shield is ground or, in your case, the negative V.
     
  19. Jun 28, 2018 #59

    BrainlordMesomorph

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    Thanks but another new (stupid) question:
    what's the right wire?

    I have the XLR cable for the long run to the pad.

    But I don't seem to to have the right wire for the interconnects between these components. Something on the order of the prewired leads on these LEDs i bought.

    I need to go buy a roll of that. (you know the blue wires from the 1979 65 in 1 kit)
    what is that?

    yes, stupid question but I was at the home depot this AM and they had 16 gauge wire, what do I need?
     
  20. Jun 29, 2018 #60

    Voyager1

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    I use medium duty (18 AWG) speaker cable (2.5 - 5 m of twin flex) for the ignition leads from my pad boxes to the rocket. Good enough for 10 - 12 A bursts. Don’t know what your blue wires are.

    16 AWG wire is probably better for you with potentially long runs, to keep the resistance down, but 18 AWG would be OK, too.
     

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