Need help with circuit to delay reed switch triggering transistor.

[Inquorate]

I need to figure out a circuit that delays a reed switch from triggering a transistor to fire a coil.

As the pendulum comes up to the apex of it's swing on one side, about 50 degrees from vertical, it closes a reed switch - in the circuit I have now, that triggers the base of a transistor which pulses a coil, which repels on the magnets on the bottom of the pendulum, pushing it into another swing.

But that's too soon: it is fighting with the pendulum's inertia.

I need the coil to fire at the moment the pendulum starts falling back down, about one third to one half of a second later. This way, I would also get use out of the magnet's attraction to the unmagnetized coil core, and can harvest a little electricity as the magnet magnetises the core.

I've tried using voltage divider circuits that have to fill up a capacitor first before reaching the approximately 1.7 volts (from a 12v source) required to trigger the base of the transistor, but this lowers the current to a point where the transistor's switched current is also affected.

What can I do to turn up the amplification of the signal in the transistor, or does anyone know of a more efficient way of approaching this problem?

I've been working on this for the greater part of 2 days now, and would really value any help.

Love and light

[Bodkins]

what about two reeds, one to fill a cap(at the apex) the next to discharge a cap to pulse the trany. they would only work if the first one is primed,
I dont now ben but i think you need a cocking the trigger thing Ye

[gyula]

Hi,

Maybe you could use a time delay circuit with the NE555 timer circuits?

See here LM555 Timer Circuits and see schematics Two Stage Time Delay Circuit with the A and B 555 timer ICs.

rgds, Gyula

[Inquorate]

Thanks guys

Read ''power-on time delay relay'' on this page. Apparently bjt transistors can be used as zener diodes, with a breakdown voltage of 6 - 9 volts.

http://ourworld.compuserve.com/homep...wden/page2.htm

How bjt transistors work

Bipolar junction transistor - Wikipedia, the free encyclopedia

I'm going with this schematic because I have the power to make -555 timers explode just by looking at them..

I'll also try the 2nd reed switch off a cap idea from bodkins.

Also, I don't know what the other two contacts are for on the reed switch. I'm using the ones that are furthest apart.

[sucahyo]

As the pendulum comes up to the apex of it's swing on one side, about 50 degrees from vertical, it closes a reed switch - in the circuit I have now, that triggers the base of a transistor which pulses a coil, which repels on the magnets on the bottom of the pendulum, pushing it into another swing.

If the pendulum and it's wire are metal, maybe you can use it as switch by attaching a strand of copper wire, which will activating the transistor by a contacting patch. I think if the wire is only used to trigger the transistor, it won't melt as long as the there is at least 100ohm resistor at transistor base.

[Inquorate]

Pendulum switch

That actually might work Sucahyo. I picked up some zener diodes that will trigger from between a resistor and a capacitor, once the capacitor reaches the zener diode's breakdown voltage. It's actually cheaper than the 555 timer chip. But Thankyou all for your suggestions and ideas.

[Inquorate]

Schematic for my coil

here it is, the gap on the left near source battery is the reed switch.

Should I use the other wire in the Bifilar coil as a pickup coil with a bridge rectifier to dump charge in the charge battery, or do you think I should just use the second wire in series or parallel with the first?

It's different to a bedini, because there's no need for a trigger coil.

Delayed+pulse+coil+circuit.jpg (image)

[gyula]

...snip
Also, I don't know what the other two contacts are for on the reed switch. I'm using the ones that are furthest apart.
...snip

Hi,

Normally reed switches have a coil (to actuate the contacts instead of moving permanent magnets) and the actual closing (or opening) contacts, this setup gives a minimum of four pins. If you check the pins (contacts) with an Ohm meter you will find the coil's DC resistance, in the some ten to some hundred Ohms range. And of course the other two pins are for the closing or opening contacts, you may check them also by the meter with the help of a small permanent magnet.

And there are reed switches (out of several types) in dual-in-line plastic cases like integrated circuits and they may have normally not used extra pins...

rgds, Gyula

[sucahyo]

Should I use the other wire in the Bifilar coil as a pickup coil with a bridge rectifier to dump charge in the charge battery, or do you think I should just use the second wire in series or parallel with the first?

You use negative collapse spike, maybe you get better spike with positive collapse spike. And I think you get less power consumption if you use single diode instead of bridge.

Will zener diode be reliable if used like that?

BTW, do the neon will still protect transistor if we parallel it with the coil?

[gyula]

here it is, the gap on the left near source battery is the reed switch.

I wonder if your reed switch is able to stay switched ON for as long as the delay time? If it can then your schematics is ok.
I mean in your schematics the transistor's collector receives the left hand side battery voltage via the reed switch and in case the reed switch is not kept ON for the needed delay time (and a bit beyond that) by the pendulum, then the transistor cannot work as a delayed switch due to the lack of the left side battery voltage (reed switch may brake voltage before the needed delay time).
Have you considered that?

rgds, Gyula

[Inquorate]

@ Sucahyo and gyula

@ Sucahyo - I'm getting the purple flash in the neon using negative collapse spike, which impresses me :-)

And that's a good point about the bridge absorbing the kickback - I did some measurements, and will now wire up the second wire of Bifilar coil in series with the first. That should create a bigger radiant spike, and also avoid the lenz drag that would have been ever present in the second wire....

I don't know if zener diode will be reliable; should be. I've seen them protecting capacitors from over charging in microwave ovens.

@ gyula - re transistor staying on long enough, I think it will: I've actually had problems with it sticking 'on' while testing on the table top, and the delay is so the coil fires just as the pendulum starts to fall - so if I use a separate magnet along the pendulum shaft and keep the relay away from the coil / pendulum magnet it should be ok. Now I know that the extra contacts on the reed switch are a coil, maybe I can route the radiant spike from the transistor thru the reed before it goes to the battery, to make sure the reed switch goes back to the off position.

Thanks for your help guys,

[Inquorate]

Had another look at my chalkboard schematic and made changes

I see what you meant gyula, and gave the transistor it's own conduit to the drive battery.

I also saw that the resistor that drains the capacitor afterwards ready for the next trigger was actually functioning as a current divider, so I changed it...

Now to start experimenting with values of caps and resistors.

Delayed+reed+transistor+coil+.jpg (image)

[Inquorate]

One more change to schematic

It needs a 1n4007 diode under the capacitor going to the source battery negative, so that the transistor to coil to source battery negative doesn't fill the cap back up..

Edit; and one more diode from source battery positive to transistor collector, so that radiant spike from coil thru neon can only go to charge battery.

Love and light

[gyula]

I see what you meant gyula, and gave the transistor it's own conduit to the drive battery.

I also saw that the resistor that drains the capacitor afterwards ready for the next trigger was actually functioning as a current divider, so I changed it...

Now to start experimenting with values of caps and resistors.

Hi, hopefully now it works as needed but its operation still depends on whether the reed switch is kept ON by the magnet for a longer than the needed delay time; if not, than the timing capacitor has not enough time to charge up for triggering.
Here is a two transistor monostable circuit that truly does what you need, see Monostable flip-flop schematics here: Circuits Page 9

the fourth topic counted up from the very bottom of that page, schematic with the two bipolar transistor (2N3904) on the left.

This could work from your 12V battery (instead of the 5V indicated) and the right hand side transistor would include your coil, the push button symbol would mean the place of your reed switch.

rgds, Gyula

[Inquorate]

It works!

It works!

BUT

The coil does not collapse quickly, meaning there is no radiant energy spike at coil collapse. And it has so little current coming from zener diode that I had to use a 2n2222 to trigger the Tip35c.

I have one 555 timer.

Wish me luck.