[simpits-chat] Altimeter Question

Stig Joergensen stig.joergensen at clearsky.dk
Tue Nov 4 14:31:41 PST 2003

Well the first T is also transistor, that gives
transistor-transistor-logic. the other type is CMOS (Complementary Metal
Oxide Semiconductor) which in fact is also a transistor
The main different between TTL and CMOS is its high/low state:
Say a device (Chip) is running at 5v, TTL will need atleast 2v to be
recognised as high where CMOS require 4v - can remember the low end
otomh (0.7v vs. 0.2v i think)
furthermore a transistor is current driven as Ben said but thats not the
hole story you need to know. Transistors is also a amplifying thingy
(symbol Hfe IIRC), this means that the current that can be driven
through emitter/collector is function of Vfe * current on basis
Take a standard BC547B transistor is have a Hfe of about 200 and can
drive 100mA, this means it only needs 100/200 = 0.5mA on its basis to be
fully opened.
One more thing about transistors - they come in two forms PNP and NPN -
think of each letter as Positive or Negative and the middle letter
states when it is fully opened eg. PNP will open more the closer you get
get to ground (0v, negative) where as NPN will open more the further
away from ground you get... (thats not entirely correct, but i cant
describe it better)
then there is saturation voltages and other stuff which i don't know
enough about to make any intelligent notes about and ive been rambling
for way too long now, so ill be getting back to my hole now....

-----Original Message-----
From: John Miguez [mailto:jmiguez at bellsouth.net]
Sent: 4. november 2003 13:47
To: Non-tech or other tech related messages for Simpits
Subject: Re: [simpits-chat] Altimeter Question

Hee hee, you younglings need an old fart to tell you about TTL.  Except,
I am having a senior moment and can't remember what the first "T" means.
The other two letters are Transistor Logic.  
Transistors came out when I was a kid.  They are these tiny replacements
for the vacuum tube that helped put a man on the moon.  :)

----- Original Message ----- 
From: Ben  <mailto:bjones at pipecomp.com.au> Jones 
To: Non-tech or other tech related  <mailto:simpits-chat at simpits.org>
messages for Simpits 
Sent: Tuesday, November 04, 2003 3:16 AM
Subject: Re: [simpits-chat] Altimeter Question

i dont know alot about the basic 2 paralax stamp , to start telling you
yes or no you can /cant do it
but from the wright up in a electronic catalogue i have  it is noted
that the stamp 2 can be connected to " push buttons, led's ,and other
TTL level devices,  and with extra components to non-TTL devices such as
relays "
so if this is correct  popping a charge via relay shouldnt be a problem
in theory
the other thought i have is what the F*** is a TTL device , i have never
heard of these  in all of my electrical studies .... but hey i get told
all the time i always have my head up my ass ... hehe,
as for modifying ya code  i might have to be solved buy a guru
programmer(s) on the list
bjones at pipecomp.com.au <mailto:bjones at pipecomp.com.au> 

----- Original Message ----- 
From: Brian  <mailto:hangr18 at hotmail.com> Sikkema 
To: simpits chat <mailto:simpits-chat at simpits.org>  
Sent: Tuesday, November 04, 2003 6:37 AM
Subject: [simpits-chat] Altimeter Question

Hey Guys,
I've got a question, not about an aircraft altimeter, but one I'm
thinking of building for model rocket use.
For those of you into the hobby, you know that even the most basic
altimeter good for data logging and, most importantly to me, ejection
charge timing, can be very expensive (cheapest I've found to do what I
need is about $120). But I've found what seems to be a very nice setup
online, here:
I'm confident I could build this altimeter and get it working, I know
enough to do that, but I'm not quite experienced enough to modify it to
what I need it to do (blow an ejection charge). This setup is just a
data-logger. What I need is for it to trip a relay at some pre-specified
altitude or time after apogee which would blow the ejection charge. This
is pretty important, because the launchsite we use up here is very
narrow, flanked by a dense forrest on one side and Lake Superior on the
other. It's nice and long, but if you drift to the side you're screwed!
I lost two rockets to the trees on our last launch, and I would have
lost my prized V2 to the Lake had the parachutes not come off on the
last flight (thats a funny story in and of itself - I'll tell it later
So anyway, long story short, anyone here have experience with PICs and
whatnot, who could take a look at the circuit and code and give me some
ideas on modding it to trip a relay? I'd be VERY appreciative! :)
If we can modify this circuit, it could be used for all sorts of useful
things, including staging. My mouth waters with the possibilities! :)


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