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?
Thanks, Mike Fisher Binder Design
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 altimeter off? Will
Binder Design wrote: ...
...
How about these?
pennant.
pennant.
How about these?
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 these.
mike cosmodrome rocketry
Wayne - that link goes to a search page, not a specific product.
Every mechanical switch bounces, some more than others. If you have a switch with very little bounce and a decoupling capacitor in the circuit the bounce will filter out.
mike cosmodrome rocketry
Mike -
The more recent AltAcc, uses an all metal screw terminal for a switch. Like these:
-Jeff Taylor
B> I'm looking for the supplier of those small PCB mount screw switches
Another poor hapless victim of Frames...
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 it.
I tried to find those about a year ago, also. Never did find the original source. The closest I got was that Electronic Goldmine
-----snip-----
How / where would you install a decoupling capacitor ? Across the switch terminals so it can act like a mini-battery to keep the altimeter powered up 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 RRC2.
John
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 problems.
mike cosmodrome rocketry
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.
mike cosmodrome rocketry
Depending
-----snip-----
So, you're telling me I have to calculate the Thevenin Equalivents.
John
Mike,
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...
Fred
John Bonnett wrote: > How / where would you install a decoupling capacitor ? Across the > switch > terminals so it can act like a mini-battery to keep the altimeter > powered up > for a few milliseconds in case the switch contacts bounce open under the > launch impulse ? >
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 tolerated.
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.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.