I think i would replace the relay with a optoisolator (digikey TLP222G-nd
looks real nice and inexpensive) with a darlington or mosfet output this
would most likely do the job ok while avoiding all of the problems
associated with the relay transistor combo

all you  would need is the opto plus a resistor in series with the led
(maybe a second led in series with that to have a visual indication.


Peter


----- Original Message -----
From: "Mike" <mrgizmo@VIANET.CA>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Tuesday, July 13, 2004 12:26 AM
Subject: Re: [EE:] Rocket timer


> Actually the "ignition" and "apogee" are both switches, yes apogee is a
> mercury tilt switch.
>
> Actually the relay will output to a camera shutter, I thought a cap would
> absorb any kickback, but I guess a diode will be better, I have some 4001
> and 4007. I will be using a 9V battery, I may switch to a mini 12V, but I
am
> not sure how it would hold up. It will not be storing data of any kind,
just
> timing cycles.
>
> > Is the "ignition" switch-looking thing a rocket ignitor?  Just in case
it
> > is, you should definitely not try to drive a rocket ignitor directly
from
> a
> > PIC output!  And what is the "apogee" switch-looking thing?  I'll assume
> its
> > a tilt-switch or something to detect nose pitch or accelerations for
now,
> > but correct me if that's not the case.  If it/they is/are [an] input(s),
> you
> > need to pull them high with something on the order of a 10k resistor to
> > ensure they don't float.  If the "ignition" thingy is an output to fire
> the
> > rocket then you need to limit the current.  I agree with what Jinx says
> > about the solenoid/relay, definitely needs a bit of bypassing if you
want
> to
> > keep your transistor & PIC around for more than a launch, but Jinx
covered
> > that very thoroughly.  I dunno about the specific diodes he recommended,
> it
> > seems any old diode you have around would do if it can handle the
> breakdown.
> > Correct me if I'm wrong guys...
> >
> > I suspect the input voltage might be coming from a 9v battery?  In that
> case
> > keep the voltage reg.  Or try stacking a few coin cells together to get
> 4.5v
> > and leave it unregulated, but make sure it can drive the coil.
> >
> > Also, are you planning on getting data out of the PIC?  Perhaps its just
> b/c
> > I don't understand the purpose of the ignition and apogee inputs, but it
> > seems if you're timing total flight time from ignition (is that a valid
> > assumption?) you'll need a way to display it as well.
> >
>
> --
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>

--
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