I’ll indirectly answer. At LDRS 36 the board voted to allow the Eggfinder WiFi switch without an external power switch in L3 certification flights because it was requested and because of two important characteristics:
1. The default mode of the WiFi switch is power off. That makes it more difficult for a person to accidentally power up their electronics while preparing their rocket.
2. Cris Erving had explained to me how his circuit used two solid state switches which must both be switched in order for the output to be on.
Nobody requested an approval of the magnetic switch, but my understanding is that its default state is power on. That’s better for recovery perhaps but could lead to accidents in the preparation area or at the pad. I honestly don’t know much more about the magnetic switch but without Adrian specifically requesting it to be approved and providing supporting data like Cris did the board has not approved it.
I'm coming into this late, but I would like to request that the Featherweight magnetic switch be allowed for arming an altimeter's deployments for a level-3 cert flight or other flights.
I support the position that a well-designed system should prevent a deployment charge from firing prematurely until the rocket is vertical and armed at the pad,
even if the altimeter has any hardware or software malfunction. This is normally done with a switch in series between the power source and the altimeter, which is open during prep and closed at the pad to arm the system. In the case of a magnetic switch, the following order of operations will guarantee the system is fault-tolerant throughout that process:
1. With no charges connected, connect the magnetic switch to the battery. This can be done days or weeks before launch. If the switch is on, then turn it off. The magnetic switch has an LED which shows when it is on, even if there is no altimeter connected to its output.
1b (optional step) Use the switch to turn on the altimeter to make sure it's ready to fly, and then power it off.
2. Connect the charges.
3. Go to the pad, and once the rocket is vertical, turn on the magnetic switch to arm the altimeter.
In answer to Steve's question, the Featherweight magnetic switch does not default to the on state. If power is disconnected and then re-connected, it will stay in the last commanded state for as long as it can "remember" what that state was. Although there isn't a fixed or guaranteed time that it will hold its state after power is removed, it's more than a few seconds, and usually it's weeks or even longer.
On a related topic, a high powered airstart is a significantly greater safety hazard than deployment charges. For high powered airstarts, I recommend requiring three series inhibits for two-fault tolerance, consistent with NASA safety requirements for catastrophic (i.e. life threatening) hazards, rather than 2 inhibits for single-fault tolerance for deployment charges. In other words, 2 independent failures can happen and the system will still be safe because the 3rd inhibit is intact. For my rockets, I add a separate mechanical switch in series with any of my airstart motor igniters, in addition to a magnetic switch and the altimeter itself. This way the rocket is safe in the prep area if up to 2 out of the 3 inhibits fail. Then when the rocket is vertical at the pad I can verify that the altimeter is working and the deployment charges are armed before arming the airstart. In my rockets I would not use a magnetic switch for more than one of the inhibits for an airstart, because an accidental exposure to a magnet (next to a pocket, for example) could turn on more than one magnetic switch at a time.