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chaztuna(at)adelphia.net
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 Posted: Tue Jul 04, 2006 4:35 pm Post subject: Switch question |
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Bob & Listers,
I wish to install a remote Ident push button for my Garmin GTX320A
transponder. I want to use a momentary push button using a standard
1/2" bushing plan form. I'm trying to select an appropriate switch
for this purpose. I called Garmin's support to find out how much
current goes through this circuit. The tech couldn't tell me, as he
did not have that info at his disposal. He did say that the
instructions said that the circuit should have no more than 0.5 amps.
When pressed further, he looked at the circuit and told me that the
switch grounded one leg of a transistor in the transponder.
I am trying to figure out if:
#1 I should specify a switch with gold (low current draw)
contacts or silver contacts? According to NKK's catalog, their
switches with gold contacts are for 0.4 amps or less.
#2 Will it matter if the contacts are fast or slow "make and break"?
#3 Required amp rating of the switch.
Charlie Kuss
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ceengland(at)bellsouth.ne
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| Posted: Tue Jul 04, 2006 5:28 pm Post subject: Switch question |
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Charlie Kuss wrote:
| Quote: |
<chaztuna(at)adelphia.net>
Bob & Listers,
I wish to install a remote Ident push button for my Garmin GTX320A
transponder. I want to use a momentary push button using a standard
1/2" bushing plan form. I'm trying to select an appropriate switch for
this purpose. I called Garmin's support to find out how much current
goes through this circuit. The tech couldn't tell me, as he did not
have that info at his disposal. He did say that the instructions said
that the circuit should have no more than 0.5 amps.
When pressed further, he looked at the circuit and told me that the
switch grounded one leg of a transistor in the transponder.
I am trying to figure out if:
#1 I should specify a switch with gold (low current draw) contacts
or silver contacts? According to NKK's catalog, their switches with
gold contacts are for 0.4 amps or less.
#2 Will it matter if the contacts are fast or slow "make and break"?
#3 Required amp rating of the switch.
Charlie Kuss
|
Hi Charlie,
I can't offer an answer with 'authority', but experience with modern
electronics would indicate that current demands should be minimal for
any switch other than the power switch (and even the power switch is
usually wimpy these days; only used to activate a solid state relay in a
lot of stuff). Call the tech back & ask him which lead of the transistor
is switched to ground. It's almost certainly the 'base' if it's a normal
silicon transistor or the 'gate' if it's an FET. If either is the case,
there will be very low current demand, likely way under 1/10 amp.
If I were doing the install in my plane, I'd just try to find something
that looked & mounted like I wanted & had good reliability with minimal
'excercise' to keep contacts clean because I wouldn't expect to be
needing the ident button very often.
I bet if you open up the xponder & look at the internal ident button, it
will be something you can buy from Mouser or Digikey for less than a dollar.
Charlie
(electronics tech in a previous life)
Slobovia Outernational
flying RV-4, -7 fuselage
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brian
Joined: 02 Jan 2006
Posts: 643
Location: Sacramento, California, USA
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| Posted: Tue Jul 04, 2006 6:27 pm Post subject: Switch question |
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On Jul 4, 2006, at 8:31 PM, Charlie Kuss wrote:
| Quote: | I am trying to figure out if:
#1 I should specify a switch with gold (low current draw)
contacts or silver contacts? According to NKK's catalog, their
switches with gold contacts are for 0.4 amps or less.
|
Go for the gold.
| Quote: |
#2 Will it matter if the contacts are fast or slow "make and
break"?
|
It shouldn't. Since the ident circuit is basically a latching timer,
it can bounce the the cows come home and that will have no effect on
the behavior of the xpdr.
| Quote: |
#3 Required amp rating of the switch.
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I would guess about 10ma -- yes, milliamps.
Brian Lloyd 361 Catterline Way
brian-yak AT lloyd DOT com Folsom, CA 95630
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
— Antoine de Saint-Exupéry
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_________________
Brian Lloyd
brian-yak at lloyd dot com
+1.916.367.2131 (voice) +1.270.912.0788 (fax)
I fly because it releases my mind from the tyranny of petty things . . .
- Antoine de Saint-Exupery |
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