I'm looking for the supplier of those small PCB mount screw switches
that are used on the Blacksky Altacc. I know Aerocon resells them, but
I'm looking for the wholesale source for them.
I'm considering changing our avionics bays to include these instead of
the key switch that they currently come with. Thoughts?
I like having a switch that can handle a "remove before flight" pennant.
I'd prefer a switch that doesn't allow the key (or whatever) to be
removed unless in the enabled position.
I bought some of the MissileWorks switches but (just like the screw
switches) there is no removable interlock that would support a pennant.
I'd been "getting away with" using a N/C phono jack but am getting
nervous as I move into higher power levels...
The phono jacks are very attractive except for the danger of "contact
bounce" causing the altimeter to power cycle. Maybe a circuit to
"debounce" that N/C connector? The N/O pole could be used to turn the
I'm curious (not having used an altimeter, yet). Both phono jack and
mechanical buttons bounce. How is one better than another?
Will Marchant wrote:
> I'd been "getting away with" using a N/C phono jack but am getting
> nervous as I move into higher power levels...
> The phono jacks are very attractive except for the danger of "contact
> bounce" causing the altimeter to power cycle. Maybe a circuit to
> "debounce" that N/C connector? The N/O pole could be used to turn the
> altimeter off?
> B> ...
> > I'm considering changing our avionics bays to include these instead of
> > the key switch that they currently come with. Thoughts?
> Will Marchant, NAR 13356, Tripoli 10125 L2
I'm not sure about bounce, but I do know that the major issues with phono
jacks is that they can short when you pull out the plug. If you look at the
male plug, you'll see two conductors separated by a (usually) black
non-conductor. The lower conductor is long enough to short the two
receptacle conductors together as it is being pulled from the receptacle.
If the circuit does not take this into account it can lead to a premature
signal to fire an ignition circuit. This is also the same reason you get a
momentary crackle in an audio system when inserting or removing one of
The more recent AltAcc, uses an all metal screw terminal for a switch.
The older AltAcc used a screw switch with a plastic base. I don't have
a source for these, but I think the newer part is better anyway.
B> I'm looking for the supplier of those small PCB mount screw switches
I think he's looking for a real switch. Something that you could stick a
screwdriver through a hole in an altimeter bay, and screw to close. This
kind of terminal requires you to have full access to wrap the wire around
How / where would you install a decoupling capacitor ? Across the
terminals so it can act like a mini-battery to keep the altimeter
for a few milliseconds in case the switch contacts bounce open under the
launch impulse ?
If so, for a 9VDC battery-powered altimeter like my RRC2, how big of a
capacitor would you recommend, and how would you bleed off the charge
when the switch is moved to the 'off' position ?
I have some key switches from All Electronics where the key can only be
removed in the 'on' position, but was leaning towards using mobo jumpers
(no moving parts) as a 'worry free' method of controlling power to the
If the switch only bounces for a few milliseconds when you first turn it on,
who cares? A key switch bounces also, and everybody uses those. Most
modern altimeters already have a big electrolytic capacitor across the power
input for this very purpose.
That's my point exactly. A small/short bounce probably won't affect us.
It's the shorting out of the phono plugs during removal that it a problem.
Instead of using open as safe, use short as safe and there will be no
The decoupling cap would go between the power and ground lines. Depending
on the circuit, this could be between the terminals of the battery. To
bleed the cap you would have to remove the voltage source and insert a load
(resistor). The size of the cap is totally dependant on the circuit, an
often use combo would be a 1uF and a 0.1uF. Again, this may all be overkill
for what we're doing. The importance is that the switch not close when it's
not supposed to.
On occasion, I used stereo phone jacks, with each channel wired in
parallel with the power. The posibility of both switch contacts bouncing
at the same time is possible, but unlikely. However, rather than use the
male phone plug, I use a 1/4" thick delron rod, (2 to 3 inches long).
Round off both ends of the rod and drill a hole in one end to attach the
streamer; wa-la, instant plug that will not short out any part of the
circuit, when removed. Before I started using delron rod, I used 1/4"
wooden candy apple sticks; don't laugh, it worked...
How big should the capacitor be? Good question. Difficult answer.
The goal is for the capacitor to provide the required current for some period of
time. So one of the variables is just how long that time is. The other two
variables are how much current is being drawn and how much voltage drop can be
The equation to compute the capacitor size is simple:
C = I * t/ V
C = capacitance in Farads (aka coulombs/volt
I = current in amperes (aka coulombs/second)
t = time in seconds
V = allowed voltage drop
Now we need to know what values to use.
Alas, most altimeters that are designed for 9V batteries use older three
terminal regulator that require fairly significant voltage in excess of the
regulated output in order to function correctly. The typical LM7805 has a
dropout voltage of 2V. Which means that the input cannot go below about 7V
before the regulator cannot maintain the output voltage. Some modern low dropout
regulators have dropout voltages of 0.1 volts or so.
So assuming that the battery is at 9V, a 2V drop is tolerable.
The other variable is how much current must be provided. Assuming for the moment
that this is 10mA, we can do some calculations.
If we want to hold things together for 1ms...
C = 0.010A * 0.001s/ 2V = 5uF
No "bleed" resistor is required as the electronics will drain the charge.