Question about switching

[dieter]

I am currently building a simple wipe, or pendulum and I want to give it a little push with an e-magnet each swing.


I realized when I push too early, it will rather brake the pendulum. So I got to push exactly in the right moment, shortly after the pendulum reached the "dead point" and then started to swing back. This way the required energy is minimal.


Only problem is, a reed switch would not know if the pendulum is still approaching or if it's already swinging away. A flip flop cirquit or a schmitt trigger don't seem to be reliable and I also don't want to use electronics, like with a hall sensor that requires: 12 V to drive the transistor, but 5 V for the sensor, whereby I'd waste energy already in pushing the 12v down to 5 using resistors...


I'd really prefere a simple, non electronic, non braking solution.


So I thought I'd ask what some of you would come up with. Any ideas?
Thanks

[MarkE]

I am currently building a simple wipe, or pendulum and I want to give it a little push with an e-magnet each swing.


I realized when I push too early, it will rather brake the pendulum. So I got to push exactly in the right moment, shortly after the pendulum reached the "dead point" and then started to swing back. This way the required energy is minimal.


Only problem is, a reed switch would not know if the pendulum is still approaching or if it's already swinging away. A flip flop cirquit or a schmitt trigger don't seem to be reliable and I also don't want to use electronics, like with a hall sensor that requires: 12 V to drive the transistor, but 5 V for the sensor, whereby I'd waste energy already in pushing the 12v down to 5 using resistors...


I'd really prefere a simple, non electronic, non braking solution.


So I thought I'd ask what some of you would come up with. Any ideas?
Thanks

Even the reed switch requires power, albeit low.  A Hall effect sensor is really the way to go from a direct measure of your field.  Alternative solutions would be an optical sensor, or even mounting a little motor to the swinging shaft and using that as a generator.

[Marsing]

$ 0.000000001   switch.

[TinselKoala]

Be sure to ignore this video, which uses neither a battery, reed switch, separate trigger winding, nor Hall sensor:

http://www.youtube.com/watch?v=0dMPQs5vpek

[Pirate88179]

Why not just use a low power 555 timer circuit?

With what you are asking for your pendulum, yes, if the timing is off it will act like a brake but.....if you set up a 555 timer circuit,
your pendulum will find equilibrium with the timing as you have it set.  You can then adjust the circuit to get the max swing you are looking for.

If you have your electromagnet fire at the "right time" every time, then your pendulum will continue to accelerate beyond what you may want.  Like pushing a kid on a swing.  When we do this, we push at the optimum time but, only for a little bit, otherwise the kid would fly off of the swing as it goes inverted.  If we did a constant timed push, the kid on the swing would get to a point that would be adjusted to the push timing, not the other way around.

Does this make sense?

Bill