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  1. #1
    Join Date
    27th June 2016
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    Continuity check on diy launch controller

    Hey all,

    I'm fairly new to rocketry still but I've been working with electronics for years with rc aircraft and other hobbies I have. I've already converted my electron beam to wireless using an eBay 315mhz remote switch but it doesn't work the best and it's missing a few features I'm planning on implementing.

    I want my launch control v2 to have a readily visible continuity check that I can see at the pad from where I'm standing to launch. My plan is to use channel 1 on the remote switch to apply power to the igniter in series with the coil of a relay. This would be protected with a low current (0.25A?) quick blow fuse for safety as well.

    I believe most who have a continuity check of some form or another use a lower voltage as well as low current to ensure the igniter isn't lit, I just want to check with those who know, would 12v in series with a relay coil be safe to do?

    Thanks


  2. #2
    Join Date
    7th February 2009
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    Quote Originally Posted by Forced_Induction View Post
    HI just want to check with those who know, would 12v in series with a relay coil be safe to do?
    Unlikely, unless the relay had an unusually high coil resistance. It would have to be greater than 1K.


  3. #3
    Join Date
    27th June 2016
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    I just checked the datasheet for the relay im planning on using (OMRON LY2NJ). 160 ohm coil, 75ma rated coil current at 12v. 0.9w power consumption.

  4. #4
    Join Date
    29th September 2014
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    Fort Worth, TX
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    A little off topic perhaps, but I used and Eggtimer Quantum for remote launch this past weekend. There is a Test mode web interface that displays continuity status. The wireless connection is via a private Wi-Fi network hosted by a SOC module on the Quatum. My remote was a Windows Phone just cause I had it handy. You should we able to use any Wi-Fi capable device with web Browser. Since the Quantum is a kit, the DIY is to correctly solder it together.
    Jack
    NAR 41185 TRA 01260

  5. #5
    Join Date
    3rd February 2012
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    So Cal (ROC, TRASD, SCRA)
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    Quote Originally Posted by Forced_Induction View Post
    Hey all,

    I'm fairly new to rocketry still but I've been working with electronics for years with rc aircraft and other hobbies I have. I've already converted my electron beam to wireless using an eBay 315mhz remote switch but it doesn't work the best and it's missing a few features I'm planning on implementing.

    I want my launch control v2 to have a readily visible continuity check that I can see at the pad from where I'm standing to launch. My plan is to use channel 1 on the remote switch to apply power to the igniter in series with the coil of a relay. This would be protected with a low current (0.25A?) quick blow fuse for safety as well.

    I believe most who have a continuity check of some form or another use a lower voltage as well as low current to ensure the igniter isn't lit, I just want to check with those who know, would 12v in series with a relay coil be safe to do?

    Thanks
    You want your continuity check in PARALLEL with the relay contacts, with a sufficiently large resistor (probably 5-10K for a LED) so that there's no chance of anything happening. If you're really paranoid, you can add a button in series with your continuity check circuit so that you have to press the button to get the light/buzzer to go. Most multi-pad relay systems have a central press-button-to-test-continuity feature at the relay/distribution box. Buzzers are nice, because everybody around you knows when you're armed. Get a pizo buzzer and you don't need a series resistor, either.

  6. #6
    Join Date
    23rd July 2011
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    I use two loops. One is a very low current continuity loop which passes 12 volts through the igniter, through a current limiting resistor, through an LED at the pad and through an LED at the control console, all in series. The igniter is connected to the two common terminals of a DPDT relay. The continuity circuit is connected to the normally connected set of terminals and the launch battery is connected to the normally open side.
    When the launch button is pressed it switches the relay contacts so the igniter is directly connected to a sealed lead acid 12v battery right at the pad.
    The LEDs are all very bright. I use 12 volts everywhere, but in the continuity loop there's a voltage drop for each series element so that the igniter never sees more than 20 mA when connected to that loop.
    I have a single battery at the console that powers all the continuity circuits for 8 pads and is used to provide current to control the relay. When I do it over (it's nearly 15 years old) I'll use a higher voltage relay control voltage so I can have longer cable runs. Right now 500 feet is about the max using silver satin phone cord from the console to each pad box.
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  7. #7
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    10th June 2013
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    cerving is correct, wire the LED across the relay contacts with a series resistor. We use 5mm super bright white LEDs with a 390 ohm series resistor. That's only .020 amps through the igniter with a 12 volt launch system which is well below the ignition current required to fire even the most sensitive igniters. These LEDs are easily visible at 300 ft.

    Steve G

  8. #8
    Join Date
    27th June 2016
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    awesome guys. I was planning on using a pair of these on a NO contact on the relay and use the continuity check circuit to power the coil of the same relay. I might just use an LED instead. thanks for the help.

  9. #9
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    That LED assembly will work fine. Just make sure you wire it across the open contacts of the relay as stated earlier. You won't need a switch at the pad as the LED will light up as soon as the igniter is connected.Click image for larger version. 

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  10. #10
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    Quote Originally Posted by sghioto View Post
    That LED assembly will work fine. Just make sure you wire it across the open contacts of the relay as stated earlier. You won't need a switch at the pad as the LED will light up as soon as the igniter is connected.Click image for larger version. 

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    If you use the schematic shown here the LED will see 12 volts whenever someone touches the clips together. You probably need a resistor in series with the LED to limit the voltage the LED sees and the current the continuity test passes.
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  11. #11
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    The LED in the schematic is the one OP was referring to. It has a series resistor built into the assembly. They didn't give the specs on the current draw but I believe it's around .040 amps from the specs of similar units.

    Steve G

  12. #12
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    Quote Originally Posted by sghioto View Post
    The LED in the schematic is the one OP was referring to. It has a series resistor built into the assembly. They didn't give the specs on the current draw but I believe it's around .040 amps from the specs of similar units.

    Steve G
    Ahh, I see. That makes sense, thanks.


    Steve Shannon
    Steve Shannon
    L3CC, TAP, Director, Tripoli Rocketry Association

  13. #13
    Join Date
    27th June 2016
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    Heres the wiring diagrams for the launch controller and the igniter at the pad. Nothing complex. I dont fly with a club so this is a project for personal use. Again, the relay should only draw 75mA through the igniter when the toggle switch is turned on.

    sequence of events: key switch on both units is turned on. Toggle switch is turned on, energizing relay through the igniter for continuity check, closing relay contacts turning leds on. the second set of contacts on the toggle switch close and when both buttons are pressed, channel 2 is activated closing the contacts and shorting power to the igniter.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  14. #14
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    26th January 2013
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    I suggest using a transistor gate and resistor as a sense for your continuity instead of placing a coil in series with an igniter. Not to say that it can't be done. Just need to account for flyback, inrush and the possibility of inadvertently creating a PFN. I would suggest a continuity current in the microamp range not milliamperes.

  15. #15
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    +1 for RFO suggestion. 75 mA is getting up there if you are using CTI electric match type igniter. I like using LEDs in series because they draw about 20 mA. Much safer.

    I would get rid of the relay all together since you aren't using it to fire the igniter and just put a momentary pushbutton, an LED and/or piezo buzzer in line with the continuity check. You want to do the check at the pad anyway because you don't want to have to do the long walk all over again if it fails.
    Handeman

    TRA #09903 L3 3/29/2015

    "If you don't use your head, you have to use your feet!" my Dad

    Tripoli Central Virginia #25 - BattlePark.org

  16. #16
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    Another option (in the schematic below) allows for a continuity check at the pad and LC if you feel you really need to use one of the extra relays in the wireless unit. If you decide to use the LED assembly mentioned then only connect one to keep the current low.
    Steve G
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  17. #17
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    Well you guys have definitely given me a lot to think about. The point about having the continuity check local rather than controlled remotely makes a lot of sense. If I'm going to do the check, I'll do it at the pad rather than where I'm launching from.

    I like the simplicity of using a 5mm led and a resistor instead and will probably go that route. I have a bag of them from replacing my interior lighting on my vehicle and they run very bright at 20ma.

  18. #18
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    You don't need to use the relay

    Click image for larger version. 

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    Just the momentary pushbutton.
    Handeman

    TRA #09903 L3 3/29/2015

    "If you don't use your head, you have to use your feet!" my Dad

    Tripoli Central Virginia #25 - BattlePark.org

  19. #19
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    I want my launch control v2 to have a readily visible continuity check that I can see at the pad from where I'm standing to launch
    I thought that was the original request. If you connect my schematic from post #9 you will have continuity visible at the pad and launch control.

    Steve G

  20. #20
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    Quote Originally Posted by sghioto View Post
    I thought that was the original request. If you connect my schematic from post #9 you will have continuity visible at the pad and launch control.

    Steve G
    I guess the relay is what is supposed to activate the continuity check for the launch controller?

    I guess I missed the part of the OP about wanting to see the indicator at the pad while at the launch controller. There isn't any data signal going back to the launch controller to show continuity status back at launch controller so you would have to use a bright light at the pad that can be seen from the launch controller. That's not much of a problem with LPR and MPR pads, but when you start getting out to the HPR safe distances it becomes more problematic, especially on bright sunny days.

    I'm beginning to think building the remote indicator that will work at long distances in bright sun shine might be harder to do then come up with the wiring.
    Handeman

    TRA #09903 L3 3/29/2015

    "If you don't use your head, you have to use your feet!" my Dad

    Tripoli Central Virginia #25 - BattlePark.org

  21. #21
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    27th June 2016
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    This project is a fluid concept, I'm not 100% stuck on anything. I'm leaning towards not having the remote continuity check after consulting these fine people. The point was made that it would be needed at the pad more than at the launch controller and this makes sense to me. I might hold on to the relay for a future cluster igniter.

  22. #22
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    Quote Originally Posted by Forced_Induction View Post
    This project is a fluid concept, I'm not 100% stuck on anything. I'm leaning towards not having the remote continuity check after consulting these fine people. The point was made that it would be needed at the pad more than at the launch controller and this makes sense to me. I might hold on to the relay for a future cluster igniter.
    Depending on your knowledge and skill levels, The best way to implement a wireless setup might be to use a couple of low cost controllers and implement a two way data connection between the pad and the controller. The human interface at the controller and the continuity and launch circuits at the pad might be the easiest part. It's the communications protocol between the two units that might be harder, although there should be quite a bit of TTP/IP and similar interface software available free online that could be used.
    Handeman

    TRA #09903 L3 3/29/2015

    "If you don't use your head, you have to use your feet!" my Dad

    Tripoli Central Virginia #25 - BattlePark.org

  23. #23
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    27th June 2016
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    I'm using a simple 2 channel 315mhz wireless switch from eBay. It's only 1 way, but it's inexpensive and easy to use. It came with a fob style transmitter but I've already hacked apart my electron beam and hooked the fob up to the switches on that. It works but I'm looking for something a bit more professional looking and seeing as how I'm going to build a better pad, I'm going to integrate the 2.

    I thought about requiring both channels to be activated in order for it to ignite but I don't know if I'm being overly cautious on that too.

  24. #24
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    Quote Originally Posted by Handeman View Post
    I'm beginning to think building the remote indicator that will work at long distances in bright sun shine might be harder to do then come up with the wiring.
    It easier to do now (better LEDs) than when I did it in 1995.

  25. #25
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    22nd May 2015
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    How much range do you get on the 315mhz switches you bought?
    Justin Bray (Videos) NAR# 102401 | TRA# 16961 | L2
    Member of Wright Stuff Rocketeers #703
    Android App: Rocket Calculator

  26. #26
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    27th June 2016
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    I haven't tested them to the limit, but the receiver antenna is still coiled up inside a project box and I've launched from 200-300ft a couple times. Clear line of sight


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