Electronic launch controller question

Electronic launch controller question

Post by jordan soldier valle » Tue, 21 Jul 1998 04:00:00



I'm trying to design am electronic launch controller with a count down
timer. The count down timer needs to start at minus 25 seconds and needs a
pause function that restarts at the same time that it paused. Can anybody
point me to any schematics, source books, etc....

-DGH-

 
 
 

Electronic launch controller question

Post by Tim » Tue, 21 Jul 1998 04:00:00


Quote:

> I'm trying to design am electronic launch controller with a count down
> timer. The count down timer needs to start at minus 25 seconds and needs a
> pause function that restarts at the same time that it paused. Can anybody
> point me to any schematics, source books, etc....

> -DGH-

I've got one that my cousin designed and built for me years ago.  It's
been through heck and has quit working, but has all those features and
more.  It was designed around radio shack parts in the late 70's or
early 80's...my mind fails me.

Countdown from up to 60 seconds and adjustable with dip switches.
Pause/continue function
Audible beep last ten seconds
LED readout
Uses 12 volt power supply (originally a GE military surplus, but
recently a gel cell)  at the pad with relay
Safety key (1/8" phono plug)
Manual Fire capability
Charge/discharge function for that old GE battery
Compact controller, built in small radio shack project box
50 feet of cable (uses flat telephone cable between controller and pad
relay)

This was used as a project in one of his classes at the UT Knoxville.
He later worked on EF-111's, etc. at Warner Robbins AFB, and now works
on avionics computers as a contracted civilian.  The controller was
designed for minimum cost to me (I didn't have much money back then) so
it has a few tradeoffs in the cost to whisbang ratio.

I'd have to get his permission to reproduce the schematics, which are
very detailed, by the way.  Does this sound like what you are looking
for?  Oh, yeah, I'd like to have another one made for myself...I promise
not to launch Composite motors off this one unless the remote box is
sealed from rocket exhaust!

Tim

 
 
 

Electronic launch controller question

Post by Darren J. Longhor » Wed, 22 Jul 1998 04:00:00




Quote:
> I'm trying to design am electronic launch controller with a count down
> timer. The count down timer needs to start at minus 25 seconds and needs a
> pause function that restarts at the same time that it paused. Can anybody
> point me to any schematics, source books, etc....

I would have thought a safer option would have been to reset the count if you
aborted it for any reason?
--
Darren J. Longhorn
UKRA98: prepped 4, flew 3, recovered 2.

http://www.geocities.com/CapeCanaveral/Hangar/8238/
 
 
 

Electronic launch controller question

Post by Tim » Wed, 22 Jul 1998 04:00:00


Quote:

> I would have thought a safer option would have been to reset the count if you
> aborted it for any reason?

NASA holds and resumes the countdown all the time.  In fact they have
built in holds even if everything is nominal.  My old setup counted down
from sixty seconds.  If I wanted to stop to check my camera, I could
without having to recycle the whole 60 seconds.  

Tim

 
 
 

Electronic launch controller question

Post by jordan soldier valle » Wed, 22 Jul 1998 04:00:00


Quote:


>> I would have thought a safer option would have been to reset the count if
you
>> aborted it for any reason?

>NASA holds and resumes the countdown all the time.  In fact they have
>built in holds even if everything is nominal.  My old setup counted down
>from sixty seconds.  If I wanted to stop to check my camera, I could
>without having to recycle the whole 60 seconds.

Can you pry the lid off and get the numbers off the chips?

-DGH-

 
 
 

Electronic launch controller question

Post by DWar » Wed, 22 Jul 1998 04:00:00


Radio Electronics many many moons ago had a construction article for a
countdown launch controller; it was only single digit and counted down from
9 to 0, but with a little knowledge about the circuits involved, it should
not be too hard to expand it to a two digit down counter; you'd have to add
the 10's digit counter, rewiring the 1's digit to down count on the carry
from the 10's; you'd also have to add additional logic (an AND circuit) to
only fire when both digits were zero.

The circuit is basically a 555 timer which pulses once every 1.5 - 2
seconds, a downcounter, a BCD to 7 segment display driver, and logic
circuitry to detect when the downcounter hit zero to fire an SCR to dump the
current to the ignitor.  the circuit had an LED to indicate continuity as
well.

The tricky part is during power-up to set the downcounter circuitry to the
desired number; in the above circuit, this was easily taken care of because
the chip's pinout allows specifying a start at 9 instead of 0.   A twin
digit countdown system would need a method to preset the starting number,
AND/OR a method to prevent triggering the SCR/ignitor(s) on power-up.

The IC used was a binary up/down counter (I believe the 74193, maybe
74192?).

 I'll see if I can find the issue date, maybe you can find a copy in the
library on microfiche/microfilm.

-Dave
Non-spammers: remove the nuclear device from my email address to respond

Quote:

>I'm trying to design am electronic launch controller with a count down
>timer. The count down timer needs to start at minus 25 seconds and needs a
>pause function that restarts at the same time that it paused. Can anybody
>point me to any schematics, source books, etc....

>-DGH-

 
 
 

Electronic launch controller question

Post by Tim » Wed, 22 Jul 1998 04:00:00


Quote:

> Can you pry the lid off and get the numbers off the chips?

> -DGH-

In the schematics it lists two CD4029 presettable binary/decade up/down
counters.  I don't know anything about electronics but I can pick out
the 555 IC that people talk about using.  It has a total of four of
them.  The drivers for the LED's are 74LS47 BCD to seven segment.  There
are several other items listed as U's such as hex inverters,  nand
gates, and dual D flip flops.  What does the U stand for?  I can pick
out S for switch, D for diode, R for resistor, P for pins, etc.

I still haven't gotten hold of the designer, but I hope to by the
weekend.

Tim

 
 
 

Electronic launch controller question

Post by Darren J. Longhor » Thu, 23 Jul 1998 04:00:00



Quote:
> NASA holds and resumes the countdown all the time.  In fact they have
> built in holds even if everything is nominal.  My old setup counted down
> from sixty seconds.  If I wanted to stop to check my camera, I could
> without having to recycle the whole 60 seconds.  

> Tim

But what if you abort at t-1?
Would you resume from there?
--
Darren J. Longhorn
UKRA98: prepped 4, flew 3, recovered 2.

http://www.geocities.com/CapeCanaveral/Hangar/8238/
 
 
 

Electronic launch controller question

Post by Robert DeHat » Thu, 23 Jul 1998 04:00:00


Quote:


> > Can you pry the lid off and get the numbers off the chips?

> > -DGH-

> In the schematics it lists two CD4029 presettable binary/decade up/down
> counters.  I don't know anything about electronics but I can pick out
> the 555 IC that people talk about using.  It has a total of four of
> them.  The drivers for the LED's are 74LS47 BCD to seven segment.  There
> are several other items listed as U's such as hex inverters,  nand
> gates, and dual D flip flops.  What does the U stand for?  I can pick
> out S for switch, D for diode, R for resistor, P for pins, etc.

> I still haven't gotten hold of the designer, but I hope to by the
> weekend.

> Tim

Why dont you just get a small electronic cooking type timer and pull the
wires off the buzzer part measure the voltage and build a sutable
driver. Seems alot easier.

RDH8

 
 
 

Electronic launch controller question

Post by Tim » Thu, 23 Jul 1998 04:00:00


Quote:

> Why dont you just get a small electronic cooking type timer and pull the
> wires off the buzzer part measure the voltage and build a sutable
> driver. Seems alot easier.

I didn't build it and don't know anything about electronics.  My
controller has hold/resume/reset features, manual launch feature,
countdown that is programmable from 99 seconds to 1 second, safety arm,
LED's to show all functions, and a relay at the pad for high current.
All this conviently fits into a small radio shack project box.  It's
probably easier to build the whole thing from scratch if you are going
to do all that.

Tim

 
 
 

Electronic launch controller question

Post by Tim » Thu, 23 Jul 1998 04:00:00


Quote:


> > NASA holds and resumes the countdown all the time.  In fact they have
> > built in holds even if everything is nominal.  My old setup counted down
> > from sixty seconds.  If I wanted to stop to check my camera, I could
> > without having to recycle the whole 60 seconds.

> > Tim

> But what if you abort at t-1?
> Would you resume from there?

I second is about the same as all the normal launchers where you push it
and it goes!  There's no safety reason not to resume from there as long
as everybody knows what's going on.  The only reason I use the countdown
is to get set for photos, I would reset and go from the top if taking a
photo.  If I'm not taking a picture, I don't care too much about
standing there for a whole minute doing nothing, so I switch over to
manual. I think your t-1 is a little overboard...my reply was to the
statement below, which seems to emply that my launcher would be safer if
I reset every time I stopped the countdown for any reason.

Quote:
> > >I would have thought a safer option would have been to reset the count if > > >you aborted it for any reason?

You didn't mention t-1, but "any reason".  Stopping at 58, 30, 15, 10,
etc. seconds would pose no problems to resume without resetting.  If
there is a problem with the launcher, the safety plug is pulled and the
launcher resets anyway.  Most rocket launches I've been to, the LCO
starts the countdown at t-5, with an occasional t-10 countdown.  

Tim

Tim

 
 
 

Electronic launch controller question

Post by Bob Kapl » Thu, 23 Jul 1998 04:00:00


Quote:


>> I would have thought a safer option would have been to reset the count if you
>> aborted it for any reason?

> NASA holds and resumes the countdown all the time.  In fact they have
> built in holds even if everything is nominal.  My old setup counted down
> from sixty seconds.  If I wanted to stop to check my camera, I could
> without having to recycle the whole 60 seconds.  

I think the point is that after some time mark, you can no longer "hold"
without "abort"ing the launch. For the Space Shuttle, this point is
essentially T-9:00. They can hold the launch at that point for perhaps
hours, but once they roll from there, they either aunch or abort for the
day.

For a model rocket launch. I'd think that any hold after the 5 second mark
would be an abort, at least back to the T-5 mark. You certainly don't want
to count to T-0:01, hold there for several minutes, then suddenly say "zero"
and push the button.

        Bob Kaplow      NAR # 18L       TRA # "Ctrl-Alt-Del"

Kaplow Klips:   http://members.aol.com/myhprcato/KaplowKlips.html
NIRA:           http://www.nira.chicago.il.us

 
 
 

Electronic launch controller question

Post by Tim » Thu, 23 Jul 1998 04:00:00


Quote:

> I think the point is that after some time mark, you can no longer "hold"
> without "abort"ing the launch. For the Space Shuttle, this point is
> essentially T-9:00. They can hold the launch at that point for perhaps
> hours, but once they roll from there, they either aunch or abort for the
> day.

> For a model rocket launch. I'd think that any hold after the 5 second mark
> would be an abort, at least back to the T-5 mark. You certainly don't want
> to count to T-0:01, hold there for several minutes, then suddenly say "zero"
> and push the button.

That's pretty much how I see it.  It's a common sense thing.  If I'm
launching by myself and I'm not photographing anything, I use a manual
launch anyway.  If I use the countdown, I normally don't have to stop
it, but I will make the decision whether to resume or reset based on
what I'm doing and who is launching with me.  Since the controller beeps
the last ten seconds, most people like to hear the whole thing, so I
reset back to 60 seconds.  

Tim

 
 
 

Electronic launch controller question

Post by Neal Bake » Thu, 23 Jul 1998 04:00:00


There is a great launch controller schematic that might fit
your needs in a book called "Advanced Model Rocketry"
published by Kalmbach Publishing. Barnes and Noble online
and Amazon.com have it available.
Quote:



> > I'm trying to design am electronic launch controller with a count down
> > timer. The count down timer needs to start at minus 25 seconds and needs a
> > pause function that restarts at the same time that it paused. Can anybody
> > point me to any schematics, source books, etc....

> I would have thought a safer option would have been to reset the count if you
> aborted it for any reason?
> --
> Darren J. Longhorn
> UKRA98: prepped 4, flew 3, recovered 2.

> http://www.geocities.com/CapeCanaveral/Hangar/8238/