back to article LOHAN's cold heart beats beneath silicon breast

Our crack Low Orbit Helium Assisted Navigator (LOHAN) electronics team has made some cracking progress over the past few weeks, putting together the beating heart that will control our audacious Vulture 2 spaceplane mission. Click here for a bigger version of the LOHAN graphic A couple of months back, we decided to fire the …

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  1. Neil Barnes Silver badge
    Boffin

    And before anyone reminds me...

    Yes, I did forget to write 'turn on the processor power' between turning all the switches off and turning switch 1 on...

  2. Anonymous Coward
    Anonymous Coward

    Boobies

    Balloon

    Or

    Orbital

    Ballocket

    Ignition

    Electronics

    System

  3. Anonymous Coward
    Anonymous Coward

    But the important question is

    But the important question is, "does it have a beeper?"

    It simply MUST have a beeper that beeps when armed.

    A count-down display is also essential.

    And of course, a red and a blue wire.

    1. Neil Barnes Silver badge

      Re: But the important question is

      Regrettable, in space, no-one can hear you beep.

      1. Mr Anonymous

        Re: But the important question is

        You're not going in to space.

    2. Peter Simpson 1
      Thumb Up

      Re: But the important question is

      Shouldn't it go "Ping!"?

      1. Dr. Mouse

        Re: But the important question is

        You also need to put in the most expensive machine in the office.

  4. Pet Peeve
    Boffin

    nice board

    Who did you use to fab your circuit boards? They're really pretty, and I'm always looking for a good place to do it. I've done some with ExpressPCB for example, but their proprietary software isn't my favorite, though their prices and build quality are decent.

    1. Pet Peeve
      Happy

      Re: nice board

      Ha, I just looked at that photo of the pcb designer again, and it looks a LOT like ExpressPCB's tool.

  5. Anonymous Coward
    Anonymous Coward

    "working on the board's schematic"?

    Looks like the PCB layout to me, not the schematic...

    1. Neil Barnes Silver badge

      Re: "working on the board's schematic"?

      The schematic's on the laptop, just visible...

      The PCB software is Eagle; not sure what Anthony used for the renders.

    2. John Deeb
      Boffin

      Re: "working on the board's schematic"?

      That's because it's probably a computer rendered pre-view, as the article indicated.

  6. Callam McMillan
    Mushroom

    Short Circuit?

    I'm not sure what kind of batteries you're using on the igniter, but is forcing a short-circuit in the event of a mission timeout such a good idea? Doesn't it risk causing a fire that could lead to a rather unwanted detonation of the rocket motor anyway?

    1. Neil Barnes Silver badge

      Re: Short Circuit?

      The idea of the short circuit is that the fuse blows, so the batteries can't fire the motor.

  7. Ed 13
    Go

    Schematic review

    R5 to R9 are 10k, and so the LED current with a 12V source will be about 1mA and you probably won't be able to see them in the sunshine. I suggest a magnitude less.

    I would be concerned that the frequency of the fail-safe timer is rather temperature dependant. I would recommend a crystal oscillator (32kHz with +/-20ppm spec over -40 to +85 are tens of pence).

    There seems to be a lack of local decoupling on the micro or any of the other ICs/Modules.

    Fuse, or otherwise protect, the incoming supplies, otherwise a loose ground wire accidentally touching of the through hole components will take tracks off you circuit board.

    IC5 will dissipate significant power. Make sure it has a decent heatsink (useful to keep the electronics warm) or use a switch mode module (about a fiver in small volume) that are nominally drop in replacements for the old 7805 devices.

    Keep up the good work!

    1. Neil Barnes Silver badge

      Re: Schematic review @ Ed and those below...

      1) Very conservative design. For the day job I build robots that steer drills three miles underground...

      2) The LEDs are 2mA high brightness types. They'll be shaded when we start. One of them goes through the relay coil and I don't want that current to persuade the relay to trigger.

      3) Failsafe timer isn't critical. We expect the electronics pack to remain close to room temperature. The oscillator is around a hundred hertz.

      4) Decoupling is there but there's not a lot of it; I may add more.

      5) IC5 dissipates milliwatts; it won't need a heatsink though it will need a mica insulating shim.

      6) Relay because that way I can get a physical separation between the coil and the contacts, and guarantee that the immediate aftermath of powering up the processor doesn't send a random glitch to the igniter.

      7) BJT rather than FET because FETs are not too happy under five volts. I'm constrained to 3v3 by the other hardware, or I need a lot of level conversion bits - extra complexity.

      8) Two transistors not because I expect a transistor to die but in case an output from the processor GPIO fails.

  8. Alan Esworthy
    Mushroom

    ORGASMIC

    Online

    Real-time

    GPS-based

    Altitude

    Sensor

    Module and

    Ignition

    Controller

  9. Mr Anonymous

    Hope there's no moisture in the relay can as it might be frozen in position when you try to fire the igniter.

    Strange choice, using a transistor to switch a relay, _ALL_ modern pyro systems use mosfets to fire igniters. Igniters usually fire with <1 amp for a few 10's of millis. I have used SP8K4 dual mosfet in a small sop8 package. Make sure you don't knock the flight package when you launch, you don't want to bounce the relay contacts.

    1. The First Dave
      Boffin

      Have you checked your relay for susceptibility to vibration/shock? It's not common, but since they are mechanical devices it _is_ possible to get a momentary contact if the shock is in the wrong direction.

      You're not trying to switch a particularly heavy load, so I would have thought solid-state stuff would be adequate.

  10. Spoon Monkey

    I'm glad it is not

    High altitute

    Ignition

    Timing

    Launch

    Electronic

    contRoller

  11. Steve Evans

    Hmmm...

    So you have two transistors for redundancy switching a single relay?

    I'm pretty sure I know which components I would have doubled up for redundancy, and it wouldn't have been the solid-state semiconductors.

    1. Pet Peeve
      Boffin

      Re: Hmmm...

      >So you have two transistors for redundancy switching a single relay?

      I don't see a problem with that. Years ago, I made some boards to control model railroad snap-relays from a PIC, and for each port, I used two pins of a nice darlington transistor chip (with on-chip back emf protection, tailor made for this) to source the relay. Relays are noisy.

      1. Pet Peeve
        Boffin

        Re: Hmmm...

        The chip was an ULN2803A. I remembered just after sending the message. Great for this kind of thing.

        1. Steve Evans

          Re: Hmmm...

          Nice chip, it looks familiar.

          My query was actually that they'd doubled up on the semiconductors, but not on the electromagnetic mechanical part... The part which could freeze solid at those altitudes.

  12. Anonymous Coward
    Anonymous Coward

    Safe

    High-altitude

    Ignition

    Timing

    System

  13. simon 43
    Pint

    Is that really???

    ...an HP-41C being used to support the design of this critical LOHAN component????

    1. Peter Simpson 1
      Thumb Up

      Re: Is that really???

      It does appear to be one of HP's greatest. I still have mine, though nowadays I tend to use its virtual version on my iPhone (i41CX) and my desktop (V41)

      RPN forever!

    2. Neil Barnes Silver badge

      Re: Is that really???

      Well spotted. I have an HP11C for the office desk, too. Had to change the batteries only last month... first time since 1987. Nothing lasts, these days.

  14. Harvey Trowell
    Thumb Up

    Backronym

    Battery-Operated On-Ballocket Jumpstart/Off-switch Board

  15. GregC

    Stratospheric

    Launch

    Apparutus

    Providing

    Pre-ignition to

    Experimental

    Rocket

    yeah, struggling with the PP....

    1. GregC

      Or more simply

      Stratospheric

      Launch

      Activation

      Gadget

  16. Steven Holmquist

    Bulgarian

    Balloon

    Using

    Leccy

    Guaranteed

    Automatic

    Rocket

    Igniter and

    Altitude

    Neutralizer

  17. Cliff

    Binary Response at Altitude

    1. Dr. Mouse
      Thumb Up

      I like this one. Nice and simple, and before launch you have to make sure LOHAN's BRA is on.

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